Plateletpheresis
Encyclopedia
Plateletpheresis is the process of collecting thrombocytes, more commonly called platelets, a component of blood involved in blood clotting
. The term specifically refers to the method of collecting the platelets, which is performed by a device used in blood donation
that separates the platelets and returns other portions of the blood to the donor. Platelet transfusion can be a life-saving procedure in preventing or treating serious complications from bleeding and hemorrhage in patients who have disorders manifesting as thrombocytopenia
(low platelet count) or platelet dysfunction. This process may also be used therapeutically to treat disorders resulting in extraordinarily high platelet counts such as essential thrombocytosis
.
for leukemia, multiple myeloma, those with aplastic anemia
, AIDS
, hypersplenism, ITP
, sepsis
, bone marrow transplant, radiation treatment, organ transplant
or surgeries such as cardiopulmonary bypass. Platelet transfusions should be avoided in those with TTP
because it can worsen neurologic symptoms and acute renal failure, presumably due to creation of new thrombi as the platelets are consumed. It should also be avoided in those with heparin-induced thrombocytopenia
(HIT) or disseminated intravascular coagulation
(DIC).http://www.sankalpindia.net/drupal/?q=apheresis/
collected in a traditional blood donation
, but there several advantages to separating the platelets at the time of collection. The first advantage is that the whole-blood platelets, sometimes called "random" platelets, from a single donation are not numerous enough for a dose to give to an adult patient. They must be pooled from several donors to create a single transfusion, and this complicates processing and increases the risk of diseases that can be spread in transfued blood, such as human immunodeficiency virus.
Collecting the platelets from a single donor also simplifies human leukocyte antigen
(HLA) matching, which improves the chance of a successful transfusion. Since it is time-consuming to find even a single compatible donor for HLA-matched transfusions, being able to collect a full dose from a single donor is much more practical than finding multiple compatible donors.
Plateletpheresis products are also easier to test for bacterial contamination, a leading cause of transfusion-associated deaths. Pooling of whole blood platelets is often done in an "open" system where the platelet containers are connected in a way that could expose the platelets to air, and pooled platelets must be transfused promptly so that any contamination does not have time to grow.
Problems with apheresis include the expense of the equipment used for collection. Whole blood platelets also do not require any additional donor recruitment, as they can be made from blood donations that are also used for packed red blood cells
and plasma
components.
, or with aplastic anemia
. If indicated, transfusions (one thrombapheresis concentrate) should be given until recovery of platelet function, generally approximately twice weekly. Surgical bleeding due solely to thrombocytopenia occurs when platelets < 50,000/µL while spontaneous bleeding occurs when platelets < 10,000/µL. Thrombocytopenic patients can develop "dry" bleeding, that is, petechiae and ecchymoses only. They will not suffer fatal hemorrhagic events unless they first have extensive mucosal bleeding, or "wet" bleeding. Therefore, in those with no bleeding or only "dry" bleeding, the threshold for transfusion should be between 5,000 to 10,000/µL. A more conservative threshold of 20,000/µL should be used in those with a fever or other risk factors for bleeding. Those with active bleeding or prior to surgery should have a threshold of 50,000/µL. An unconfirmed, but helpful, way to determine whether a patient is recovering from chemotherapy-induced thrombocytopenia is to measure "reticulated" platelets, or young RNA-containing platelets, which signifies that the patient is starting to make new platelets.
or drug-induced thrombocytopenia. Platelet transfusions are generally not recommended for this group of patients because the underlying cause involves antibodies that destroy platelets, therefore any newly transfused platelets will also be destroyed. More studies need to be done.
(dDAVP). Transfusion is not necessarily required. However, with some more severe disorders such as Glanzmann thrombasthenia, transfusions with large amount of platelets may be needed. The number of transfusions may be reduced if these patients are given recombinant human factor VIIa since the underlying cause are antibodies to platelet glycoproteins IIb/IIIa.
, and its similar drug class, the NSAIDs. Other antiplatelet drugs are commonly prescribed for patients with acute coronary syndromes such as clopidogrel
and ticlopidine
. When surgery is undertaken following the administration of these drugs, bleeding can be serious. Transfusion under these circumstances is not clear-cut and one has to use clinical judgment in these cases.
The theoretical value of the CCI is 20,000/μL but clinically, the value is closer to 10,000/μL. If the CCI is less than 5,000/μL, patients are said to have "refractoriness" to platelet transfusion.
(see apheresis
). The earliest manual forms of thrombapheresis are done by the separation of platelets from multiple bags of whole blood
collected from donors or blood sellers. Since each blood bag (usually 250 mL or 500 mL) contains a relatively small number of platelets, it can take as many as a dozen blood bags (usually from 5 to 10 bags, depending on the size of the blood bags and each donor's platelet count) to accumulate a single unit of platelets (enough for one patient). This greatly increases the risks of the transfusion. Each unit of platelets separated from donated whole blood is called a "platelet concentrate".
Modern automatic thrombapheresis allows blood donors to give a portion of their platelets, while keeping their red blood cells and at least a portion of blood plasma
. Therefore, no more than three units of platelets are generally harvested in any one sitting from a donor. Most donors will donate a "single" or "double" unit, however the occurrence of "triples" has been increasing as more suitable donors are recruited.
Because platelets have a life-span of just 5 days, more platelet donors are always needed. Some centers are experimenting with 7 day platelets, but this requires additional testing and the lack of any preservative solutions means that the product is far more effective when fresh.
Even though red blood cells can also be collected in the process, most blood donation organizations do not do so because it takes much longer for the human body to replenish their loss. If the donor donates both red blood cells and platelets, it takes months, rather than days or weeks, before they are allowed to donate again (the guidelines regarding blood donation intervals are country-specific).
In most cases, blood plasma is returned to the donor as well. However, in locations that have plasma processing facilities, a part of the donor's plasma can also be collected in a separate blood bag (see plasmapheresis
).
, white blood cells are collected as an unwanted component with the platelets. Since it takes up to 3 liters of whole blood (the amount of a dozen blood bags) to generate a dose of platelets, white blood cells from one or several donors will also be collected along with the platelets. A 70 kg (154 lb) man has only about 6 liters of blood. If all of the incidentally collected white blood cells are transfused with the platelets, substantial rejection problems can occur. Therefore, it is standard practice to filter out white blood cells before transfusion by the process of leukoreduction
.
Early platelet transfusions used a filter to remove white blood cells at the time of transfusion. It takes a trained person about 10 minutes to assemble the equipment, and this is not the safest or most efficient means of filtration because living white blood cells can release cytokine
s during storage and dead white blood cells can break up into smaller fragments that can still stimulate a dangerous response from the immune system. In addition, simple filtration can lead to increased risks of infection and loss of valuable platelets. Newer, more advanced thrombapheresis machines can filter white blood cells during separation.
For example, with marginally acceptable whole blood (white blood cells: < 10,000/mm³; platelets: > 150,000/mm³), a dose (3×1011) of platelets comes with about 2×1010 white blood cells. This can seriously damage the patient's health. A dose of single-donor platelets prepared using latest filters can contain as little as 5×106 white blood cells.
(BC) is more widely used in Europe.
Platelets are the clotting factor of the blood, and when donated, frequently go to cancer patients, because due to chemotherapy
many cancer patients are unable to generate enough platelets of their own.
The basic principles of automatic platelet apheresis
are the same as in the manual procedure, but the whole procedure is performed by a computer-controlled machine. Since the donor's blood is processed in a sterile single-use centrifuge, the unwanted components can be returned to the donor safely. This allows the apheresis machine to repeat the draw-centrifuge-return cycle to obtain more platelets. The bulk of the machine and the length of the donation process means most platelet donations are done in blood centers instead of mobile blood drives.
Each country has its own rules to protect the safety of both donor and recipient. In a typical set of rules, a platelet donor must weigh at least 50 kg (110 lb) and have a platelet count of at least 150 x 109/L (150,000 platelets per mm³).
One unit has about 3×1011 platelets. Therefore, it takes 2 liters of blood having a platelet count of 150,000/mm³ to produce one unit of platelets. Some regular donors have higher platelet counts (over 300,000/mm³); for those donors, it only takes about one liter of their blood to produce a unit. Since the machine used to perform the procedure uses suction to pull blood out of your body, some people that can give whole blood may have veins too small to use for platelet donation. Your blood center can evaluate you prior to donation.
Blood accounts for about 8% of body weight, giving a 50 kg (110 lb) donor about four liters of blood. No more than 50% of platelets are ever extracted in one sitting, and they can be replenished by the body in about three days.
Most newer apheresis machines can separate a dose of platelets in about 60 to 120 minutes depending on the donor's health condition.
, the donor is taken into the donation room and sits in a chair next to the machine. The technician cleans one or both arms with iodine, or other disinfectant, and inserts the catheter
into a vein
in the arm. With some procedures both arms are used, one to draw blood and the other to return it. The process takes about one to two hours while blood is pulled into the machine, mixed with an anticoagulant such as sodium citrate
, spun around, and returned to the donor. "Double needle" procedures using both arms tend to be shorter since the blood is drawn and returned through different catheters; with "single needle" procedures a set volume is drawn and processed in the first part of the cycle and returned in the second part. The donor's blood undertakes 3-4 cycles of draw and return.
Side effects of the donation of platelets generally fall into three categories: blood pressure changes, problems with vein access, and effects of the returned anticoagulant. Blood pressure changes can sometimes cause nausea, fatigue, and dizziness. Venous access problems can cause bruising, referred to as a hematoma
. While donating, the lips may begin to tingle or there may be a metallic taste; a supply of calcium antacid
tablets is usually kept close by because the anticoagulant works by binding to the calcium
in the blood. Since calcium is used in the operation of the nervous system, nerve-ending-dense areas (such as the lips) are susceptible to the tingling. The donation process can also cause more serious problems such as fainting, and nerve irritation. These problems are extremely rare, but apheresis donors are typically not allowed to sleep during the long donation process so that they can be monitored.
Aside from the procedure, donating platelets is different from donating blood in a few ways.
Firstly, the donor must not take aspirin
or other anti-platelet
medications such as such as clopidogrel
(Plavix) for anywhere from 36 to 72 hours prior to donation. (Guidelines vary by blood center.) The reason for this is that aspirin can prevent platelets from adhering. Some blood centers also prohibit the taking of any NSAID (non-steroidal-anti-inflammatory-drug) for 36 hours prior.
Secondly, one is generally allowed to donate platelets anywhere from every 3–28 days. This is a stark contrast to whole-blood donation, which has an eight-week (or longer) waiting period between donations. Along those lines, since platelet donation does temporarily remove whole-blood from the body, it may become necessary to wait eight weeks after a whole blood donation to donate platelets. In the US, a donor is only allowed to donate 24 times each year and may not lose more red blood cells or plasma in a year than they would from the maximum allowable number of whole blood donations.
Thirdly, additional tests may be required before becoming a donor for the first time. These tests are used to establish a platelet count, and also possibly to determine the donor's compatibility with particular recipients through an HLA (Human Leukocyte Antigen
) test. Multiparous women may be excluded from becoming donors due to heightened TRALI risk. The tests usually involve nothing more involved than the drawing of several tubes of blood.
oil (or the insides of a Vitamin E capsule) on the venipuncture site may reduce scarring.
Scarring of veins may also cause problems for further attempts to draw blood, such as for medical procedures. This may confuse phlebotomists who may believe they have missed the vein due to the higher pressure needed to penetrate the scar tissue.
Hemostasis
Hemostasis or haemostasis is a process which causes bleeding to stop, meaning to keep blood within a damaged blood vessel . Most of the time this includes blood changing from a liquid to a solid state. Intact blood vessels are central to moderating blood's tendency to clot...
. The term specifically refers to the method of collecting the platelets, which is performed by a device used in blood donation
Blood donation
A blood donation occurs when a person voluntarily has blood drawn and used for transfusions or made into medications by a process called fractionation....
that separates the platelets and returns other portions of the blood to the donor. Platelet transfusion can be a life-saving procedure in preventing or treating serious complications from bleeding and hemorrhage in patients who have disorders manifesting as thrombocytopenia
Thrombocytopenia
Thrombocytopenia is a relative decrease of platelets in blood.A normal human platelet count ranges from 150,000 to 450,000 platelets per microliter of blood. These limits are determined by the 2.5th lower and upper percentile, so values outside this range do not necessarily indicate disease...
(low platelet count) or platelet dysfunction. This process may also be used therapeutically to treat disorders resulting in extraordinarily high platelet counts such as essential thrombocytosis
Essential thrombocytosis
Essential thrombocythemia is a rare chronic blood disorder characterized by the overproduction of platelets by megakaryocytes in the bone marrow in the absence of an alternative cause. In some cases this disorder may be progressive, and rarely may evolve into acute myeloid leukemia or myelofibrosis...
.
Platelet transfusion
Platelet transfusions are traditionally given to those undergoing chemotherapyChemotherapy
Chemotherapy is the treatment of cancer with an antineoplastic drug or with a combination of such drugs into a standardized treatment regimen....
for leukemia, multiple myeloma, those with aplastic anemia
Aplastic anemia
Aplastic anemia is a condition where bone marrow does not produce sufficient new cells to replenish blood cells. The condition, per its name, involves both aplasia and anemia...
, AIDS
AIDS
Acquired immune deficiency syndrome or acquired immunodeficiency syndrome is a disease of the human immune system caused by the human immunodeficiency virus...
, hypersplenism, ITP
Idiopathic thrombocytopenic purpura
Idiopathic thrombocytopenic purpura is the condition of having an abnormally low platelet count of no known cause . As most incidents of ITP appear to be related to the production of antibodies against platelets, immune thrombocytopenic purpura or immune thrombocytopenia are terms also used to...
, sepsis
Sepsis
Sepsis is a potentially deadly medical condition that is characterized by a whole-body inflammatory state and the presence of a known or suspected infection. The body may develop this inflammatory response by the immune system to microbes in the blood, urine, lungs, skin, or other tissues...
, bone marrow transplant, radiation treatment, organ transplant
Organ transplant
Organ transplantation is the moving of an organ from one body to another or from a donor site on the patient's own body, for the purpose of replacing the recipient's damaged or absent organ. The emerging field of regenerative medicine is allowing scientists and engineers to create organs to be...
or surgeries such as cardiopulmonary bypass. Platelet transfusions should be avoided in those with TTP
Thrombotic thrombocytopenic purpura
Thrombotic thrombocytopenic purpura is a rare disorder of the blood-coagulation system, causing extensive microscopic thromboses to form in small blood vessels throughout the body...
because it can worsen neurologic symptoms and acute renal failure, presumably due to creation of new thrombi as the platelets are consumed. It should also be avoided in those with heparin-induced thrombocytopenia
Heparin-induced thrombocytopenia
Heparin-induced thrombocytopenia is the development of thrombocytopenia , due to the administration of various forms of heparin, an anticoagulant...
(HIT) or disseminated intravascular coagulation
Disseminated intravascular coagulation
Disseminated intravascular coagulation , also known as disseminated intravascular coagulopathy or consumptive coagulopathy, is a pathological activation of coagulation mechanisms that happens in response to a variety of diseases. DIC leads to the formation of small blood clots inside the blood...
(DIC).http://www.sankalpindia.net/drupal/?q=apheresis/
Plateletpheresis and whole blood platelets
Not all platelet transfusions use platelets collected by automated apheresis. The platelets can also be separated from donations of whole bloodWhole blood
Whole blood is a term used in transfusion medicine for human blood from a standard blood donation. The blood is typically combined with an anticoagulant during the collection process, but is generally otherwise unprocessed...
collected in a traditional blood donation
Blood donation
A blood donation occurs when a person voluntarily has blood drawn and used for transfusions or made into medications by a process called fractionation....
, but there several advantages to separating the platelets at the time of collection. The first advantage is that the whole-blood platelets, sometimes called "random" platelets, from a single donation are not numerous enough for a dose to give to an adult patient. They must be pooled from several donors to create a single transfusion, and this complicates processing and increases the risk of diseases that can be spread in transfued blood, such as human immunodeficiency virus.
Collecting the platelets from a single donor also simplifies human leukocyte antigen
Human leukocyte antigen
The human leukocyte antigen system is the name of the major histocompatibility complex in humans. The super locus contains a large number of genes related to immune system function in humans. This group of genes resides on chromosome 6, and encodes cell-surface antigen-presenting proteins and...
(HLA) matching, which improves the chance of a successful transfusion. Since it is time-consuming to find even a single compatible donor for HLA-matched transfusions, being able to collect a full dose from a single donor is much more practical than finding multiple compatible donors.
Plateletpheresis products are also easier to test for bacterial contamination, a leading cause of transfusion-associated deaths. Pooling of whole blood platelets is often done in an "open" system where the platelet containers are connected in a way that could expose the platelets to air, and pooled platelets must be transfused promptly so that any contamination does not have time to grow.
Problems with apheresis include the expense of the equipment used for collection. Whole blood platelets also do not require any additional donor recruitment, as they can be made from blood donations that are also used for packed red blood cells
Packed red blood cells
In transfusion medicine, packed red blood cells are red blood cells that have been separated from whole blood for transfusion purposes. The product is typically abbreviated RBC or PRBC, and sometimes LRBC for leukoreduced products...
and plasma
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
components.
Thrombocytopenia due to underproduction
Recipients in this category include those undergoing chemotherapy, those with myelophthisic anemia, AIDSAIDS
Acquired immune deficiency syndrome or acquired immunodeficiency syndrome is a disease of the human immune system caused by the human immunodeficiency virus...
, or with aplastic anemia
Aplastic anemia
Aplastic anemia is a condition where bone marrow does not produce sufficient new cells to replenish blood cells. The condition, per its name, involves both aplasia and anemia...
. If indicated, transfusions (one thrombapheresis concentrate) should be given until recovery of platelet function, generally approximately twice weekly. Surgical bleeding due solely to thrombocytopenia occurs when platelets < 50,000/µL while spontaneous bleeding occurs when platelets < 10,000/µL. Thrombocytopenic patients can develop "dry" bleeding, that is, petechiae and ecchymoses only. They will not suffer fatal hemorrhagic events unless they first have extensive mucosal bleeding, or "wet" bleeding. Therefore, in those with no bleeding or only "dry" bleeding, the threshold for transfusion should be between 5,000 to 10,000/µL. A more conservative threshold of 20,000/µL should be used in those with a fever or other risk factors for bleeding. Those with active bleeding or prior to surgery should have a threshold of 50,000/µL. An unconfirmed, but helpful, way to determine whether a patient is recovering from chemotherapy-induced thrombocytopenia is to measure "reticulated" platelets, or young RNA-containing platelets, which signifies that the patient is starting to make new platelets.
Immune thrombocytopenia
Recipients in this category include those with ITPIdiopathic thrombocytopenic purpura
Idiopathic thrombocytopenic purpura is the condition of having an abnormally low platelet count of no known cause . As most incidents of ITP appear to be related to the production of antibodies against platelets, immune thrombocytopenic purpura or immune thrombocytopenia are terms also used to...
or drug-induced thrombocytopenia. Platelet transfusions are generally not recommended for this group of patients because the underlying cause involves antibodies that destroy platelets, therefore any newly transfused platelets will also be destroyed. More studies need to be done.
Altered platelet functions
Disorders of platelet function can be congenital or acquired. Most of these disorders are mild and may respond to therapy with desmopressinDesmopressin
Desmopressin is a synthetic replacement for vasopressin, the hormone that reduces urine production. It may be taken nasally, intravenously, or as a tablet...
(dDAVP). Transfusion is not necessarily required. However, with some more severe disorders such as Glanzmann thrombasthenia, transfusions with large amount of platelets may be needed. The number of transfusions may be reduced if these patients are given recombinant human factor VIIa since the underlying cause are antibodies to platelet glycoproteins IIb/IIIa.
Cardiopulmonary bypass surgery
This surgery can result in destruction of a large proportion of the patient's platelets and may render the remaining viable platelets to be dysfunctional. The indications for transfusion in such patients is controversial. General guidelines recommend not transfusing patients prophylactically but only when they are bleeding excessively, while also giving desmopressin.Drug-induced platelet dysfunction
The most common of these is aspirinAspirin
Aspirin , also known as acetylsalicylic acid , is a salicylate drug, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication. It was discovered by Arthur Eichengrun, a chemist with the German company Bayer...
, and its similar drug class, the NSAIDs. Other antiplatelet drugs are commonly prescribed for patients with acute coronary syndromes such as clopidogrel
Clopidogrel
Clopidogrel is an oral, thienopyridine class antiplatelet agent used to inhibit blood clots in coronary artery disease, peripheral vascular disease, and cerebrovascular disease. It is marketed by Bristol-Myers Squibb and Sanofi-Aventis under the trade name Plavix. The drug works by irreversibly...
and ticlopidine
Ticlopidine
Ticlopidine is an antiplatelet drug in the thienopyridine family. Like clopidogrel, it is an adenosine diphosphate receptor inhibitor. It is used in patients in whom aspirin is not tolerated, or in whom dual antiplatelet therapy is desirable...
. When surgery is undertaken following the administration of these drugs, bleeding can be serious. Transfusion under these circumstances is not clear-cut and one has to use clinical judgment in these cases.
Expected platelet increase after transfusion
Platelet count increase as well as platelet survival after transfusion is related to the dose of platelets infused and to the patient's body surface area (BSA). Usually these values are less than what would be expected.- Corrected platelet count increment (CCI) = platelet increment at one hr x BSA (m2) / # platelets infused x 1011
- Expected platelet increase (per μL) = platelets infused x CCI / BSA (m2)
The theoretical value of the CCI is 20,000/μL but clinically, the value is closer to 10,000/μL. If the CCI is less than 5,000/μL, patients are said to have "refractoriness" to platelet transfusion.
Platelet collection
The separation of individual blood components is done with a specialized centrifugeCentrifuge
A centrifuge is a piece of equipment, generally driven by an electric motor , that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis...
(see apheresis
Apheresis
Apheresis is a medical technology in which the blood of a donor or patient is passed through an apparatus that separates out one particular constituent and returns the remainder to the circulation...
). The earliest manual forms of thrombapheresis are done by the separation of platelets from multiple bags of whole blood
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
collected from donors or blood sellers. Since each blood bag (usually 250 mL or 500 mL) contains a relatively small number of platelets, it can take as many as a dozen blood bags (usually from 5 to 10 bags, depending on the size of the blood bags and each donor's platelet count) to accumulate a single unit of platelets (enough for one patient). This greatly increases the risks of the transfusion. Each unit of platelets separated from donated whole blood is called a "platelet concentrate".
Modern automatic thrombapheresis allows blood donors to give a portion of their platelets, while keeping their red blood cells and at least a portion of blood plasma
Blood plasma
Blood plasma is the straw-colored liquid component of blood in which the blood cells in whole blood are normally suspended. It makes up about 55% of the total blood volume. It is the intravascular fluid part of extracellular fluid...
. Therefore, no more than three units of platelets are generally harvested in any one sitting from a donor. Most donors will donate a "single" or "double" unit, however the occurrence of "triples" has been increasing as more suitable donors are recruited.
Because platelets have a life-span of just 5 days, more platelet donors are always needed. Some centers are experimenting with 7 day platelets, but this requires additional testing and the lack of any preservative solutions means that the product is far more effective when fresh.
Even though red blood cells can also be collected in the process, most blood donation organizations do not do so because it takes much longer for the human body to replenish their loss. If the donor donates both red blood cells and platelets, it takes months, rather than days or weeks, before they are allowed to donate again (the guidelines regarding blood donation intervals are country-specific).
In most cases, blood plasma is returned to the donor as well. However, in locations that have plasma processing facilities, a part of the donor's plasma can also be collected in a separate blood bag (see plasmapheresis
Plasmapheresis
Plasmapheresis is the removal, treatment, and return of blood plasma from blood circulation. It is thus an extracorporeal therapy...
).
Leukoreduction
Due to their higher relative densityRelative density
Relative density, or specific gravity, is the ratio of the density of a substance to the density of a given reference material. Specific gravity usually means relative density with respect to water...
, white blood cells are collected as an unwanted component with the platelets. Since it takes up to 3 liters of whole blood (the amount of a dozen blood bags) to generate a dose of platelets, white blood cells from one or several donors will also be collected along with the platelets. A 70 kg (154 lb) man has only about 6 liters of blood. If all of the incidentally collected white blood cells are transfused with the platelets, substantial rejection problems can occur. Therefore, it is standard practice to filter out white blood cells before transfusion by the process of leukoreduction
Leukoreduction
Leukoreduction is the removal of white blood cells from the blood or blood components supplied for blood transfusion. After the removal of the leukocytes, the blood product is said to be leukoreduced.- Benefits and costs :...
.
Early platelet transfusions used a filter to remove white blood cells at the time of transfusion. It takes a trained person about 10 minutes to assemble the equipment, and this is not the safest or most efficient means of filtration because living white blood cells can release cytokine
Cytokine
Cytokines are small cell-signaling protein molecules that are secreted by the glial cells of the nervous system and by numerous cells of the immune system and are a category of signaling molecules used extensively in intercellular communication...
s during storage and dead white blood cells can break up into smaller fragments that can still stimulate a dangerous response from the immune system. In addition, simple filtration can lead to increased risks of infection and loss of valuable platelets. Newer, more advanced thrombapheresis machines can filter white blood cells during separation.
For example, with marginally acceptable whole blood (white blood cells: < 10,000/mm³; platelets: > 150,000/mm³), a dose (3×1011) of platelets comes with about 2×1010 white blood cells. This can seriously damage the patient's health. A dose of single-donor platelets prepared using latest filters can contain as little as 5×106 white blood cells.
Apheresis
There are two types of manual platelet apheresis. Platelet-rich plasma (PRP) is widely used in North America and Buffy coatBuffy coat
The buffy coat is the fraction of an anticoagulated blood sample after density gradient centrifugation that contains most of the white blood cells and platelets.-Description:...
(BC) is more widely used in Europe.
Platelets are the clotting factor of the blood, and when donated, frequently go to cancer patients, because due to chemotherapy
Chemotherapy
Chemotherapy is the treatment of cancer with an antineoplastic drug or with a combination of such drugs into a standardized treatment regimen....
many cancer patients are unable to generate enough platelets of their own.
The basic principles of automatic platelet apheresis
Apheresis
Apheresis is a medical technology in which the blood of a donor or patient is passed through an apparatus that separates out one particular constituent and returns the remainder to the circulation...
are the same as in the manual procedure, but the whole procedure is performed by a computer-controlled machine. Since the donor's blood is processed in a sterile single-use centrifuge, the unwanted components can be returned to the donor safely. This allows the apheresis machine to repeat the draw-centrifuge-return cycle to obtain more platelets. The bulk of the machine and the length of the donation process means most platelet donations are done in blood centers instead of mobile blood drives.
Each country has its own rules to protect the safety of both donor and recipient. In a typical set of rules, a platelet donor must weigh at least 50 kg (110 lb) and have a platelet count of at least 150 x 109/L (150,000 platelets per mm³).
One unit has about 3×1011 platelets. Therefore, it takes 2 liters of blood having a platelet count of 150,000/mm³ to produce one unit of platelets. Some regular donors have higher platelet counts (over 300,000/mm³); for those donors, it only takes about one liter of their blood to produce a unit. Since the machine used to perform the procedure uses suction to pull blood out of your body, some people that can give whole blood may have veins too small to use for platelet donation. Your blood center can evaluate you prior to donation.
Blood accounts for about 8% of body weight, giving a 50 kg (110 lb) donor about four liters of blood. No more than 50% of platelets are ever extracted in one sitting, and they can be replenished by the body in about three days.
Most newer apheresis machines can separate a dose of platelets in about 60 to 120 minutes depending on the donor's health condition.
Platelet donation
After a short physical examinationPhysical examination
Physical examination or clinical examination is the process by which a doctor investigates the body of a patient for signs of disease. It generally follows the taking of the medical history — an account of the symptoms as experienced by the patient...
, the donor is taken into the donation room and sits in a chair next to the machine. The technician cleans one or both arms with iodine, or other disinfectant, and inserts the catheter
Catheter
In medicine, a catheter is a tube that can be inserted into a body cavity, duct, or vessel. Catheters thereby allow drainage, administration of fluids or gases, or access by surgical instruments. The process of inserting a catheter is catheterization...
into a vein
Route of administration
A route of administration in pharmacology and toxicology is the path by which a drug, fluid, poison, or other substance is taken into the body.-Classification:Routes of administration are usually classified by application location...
in the arm. With some procedures both arms are used, one to draw blood and the other to return it. The process takes about one to two hours while blood is pulled into the machine, mixed with an anticoagulant such as sodium citrate
Sodium citrate
Trisodium citrate has the chemical formula of Na3C6H5O7. It is sometimes referred to simply as sodium citrate, though sodium citrate can refer to any of the three sodium salts of citric acid. It possesses a saline, mildly tart flavor. For this reason, citrates of certain alkaline and alkaline earth...
, spun around, and returned to the donor. "Double needle" procedures using both arms tend to be shorter since the blood is drawn and returned through different catheters; with "single needle" procedures a set volume is drawn and processed in the first part of the cycle and returned in the second part. The donor's blood undertakes 3-4 cycles of draw and return.
Side effects of the donation of platelets generally fall into three categories: blood pressure changes, problems with vein access, and effects of the returned anticoagulant. Blood pressure changes can sometimes cause nausea, fatigue, and dizziness. Venous access problems can cause bruising, referred to as a hematoma
Hematoma
A hematoma, or haematoma, is a localized collection of blood outside the blood vessels, usually in liquid form within the tissue. This distinguishes it from an ecchymosis, which is the spread of blood under the skin in a thin layer, commonly called a bruise...
. While donating, the lips may begin to tingle or there may be a metallic taste; a supply of calcium antacid
Antacid
An antacid is a substance which neutralizes stomach acidity.-Mechanism of action:Antacids perform a neutralization reaction, increasing the pH to reduce acidity in the stomach. When gastric hydrochloric acid reaches the nerves in the gastrointestinal mucosa, they signal pain to the central nervous...
tablets is usually kept close by because the anticoagulant works by binding to the calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
in the blood. Since calcium is used in the operation of the nervous system, nerve-ending-dense areas (such as the lips) are susceptible to the tingling. The donation process can also cause more serious problems such as fainting, and nerve irritation. These problems are extremely rare, but apheresis donors are typically not allowed to sleep during the long donation process so that they can be monitored.
Aside from the procedure, donating platelets is different from donating blood in a few ways.
Firstly, the donor must not take aspirin
Aspirin
Aspirin , also known as acetylsalicylic acid , is a salicylate drug, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication. It was discovered by Arthur Eichengrun, a chemist with the German company Bayer...
or other anti-platelet
Platelet
Platelets, or thrombocytes , are small,irregularly shaped clear cell fragments , 2–3 µm in diameter, which are derived from fragmentation of precursor megakaryocytes. The average lifespan of a platelet is normally just 5 to 9 days...
medications such as such as clopidogrel
Clopidogrel
Clopidogrel is an oral, thienopyridine class antiplatelet agent used to inhibit blood clots in coronary artery disease, peripheral vascular disease, and cerebrovascular disease. It is marketed by Bristol-Myers Squibb and Sanofi-Aventis under the trade name Plavix. The drug works by irreversibly...
(Plavix) for anywhere from 36 to 72 hours prior to donation. (Guidelines vary by blood center.) The reason for this is that aspirin can prevent platelets from adhering. Some blood centers also prohibit the taking of any NSAID (non-steroidal-anti-inflammatory-drug) for 36 hours prior.
Secondly, one is generally allowed to donate platelets anywhere from every 3–28 days. This is a stark contrast to whole-blood donation, which has an eight-week (or longer) waiting period between donations. Along those lines, since platelet donation does temporarily remove whole-blood from the body, it may become necessary to wait eight weeks after a whole blood donation to donate platelets. In the US, a donor is only allowed to donate 24 times each year and may not lose more red blood cells or plasma in a year than they would from the maximum allowable number of whole blood donations.
Thirdly, additional tests may be required before becoming a donor for the first time. These tests are used to establish a platelet count, and also possibly to determine the donor's compatibility with particular recipients through an HLA (Human Leukocyte Antigen
Human leukocyte antigen
The human leukocyte antigen system is the name of the major histocompatibility complex in humans. The super locus contains a large number of genes related to immune system function in humans. This group of genes resides on chromosome 6, and encodes cell-surface antigen-presenting proteins and...
) test. Multiparous women may be excluded from becoming donors due to heightened TRALI risk. The tests usually involve nothing more involved than the drawing of several tubes of blood.
Vein scarring
Repeated platelet donations at short intervals will cause the venipuncture site to scar. While cosmetically it is virtually invisible, the scarring also occurs on the vein itself, making it harder to insert a needle on future occasions. Anecdotal reports have said that rubbing Vitamin EVitamin E
Vitamin E is used to refer to a group of fat-soluble compounds that include both tocopherols and tocotrienols. There are many different forms of vitamin E, of which γ-tocopherol is the most common in the North American diet. γ-Tocopherol can be found in corn oil, soybean oil, margarine and dressings...
oil (or the insides of a Vitamin E capsule) on the venipuncture site may reduce scarring.
Scarring of veins may also cause problems for further attempts to draw blood, such as for medical procedures. This may confuse phlebotomists who may believe they have missed the vein due to the higher pressure needed to penetrate the scar tissue.