Monospot test
Encyclopedia
The test is sensitive for heterophile
antibodies produced by the human immune system
in response to EBV infection.
The monospot test, a form of the heterophile antibody test, is a rapid test for infectious mononucleosis
due to Epstein–Barr virus (EBV). Commercially-available test kits are 70-92% sensitive
and 96-100% specific
. It will generally not be positive during the 4-6 week incubation period before the onset of symptoms. It will also not generally be positive after active infection has subsided, even though the virus persists in the same cells in the body for the rest of the carrier's life.
A 20% suspension of horse red cells is used in an isotonic 3-8 % sodium citrate formulation.
One drop of the patient’s serum to be tested is mixed on an opal glass slide with one drop of a particulate suspension of guinea-pig kidney stroma, and a suspension of beef red cell stroma; sera and suspensions are mixed with a wooden applicator for 10 times.
Ten micro liter of the horse red cell suspension are then added and mixed with each drop of absorbed serum.
The mixture is left undisturbed for one minute (not rocked or shaken).
Examine for the presence or absence of red cell agglutination.
If stronger with the sera absorbed with guinea-pig kidney, the test is positive.
If stronger with the sera absorbed with beef red cell stroma, the test is negative.
If agglutination is absent in both mixtures, the test is negative.
A known 'positive' and 'negative' control serum is tested with each batch of test sera.
, typically in the presence of clinical features such as fever, malaise, pharyngitis, tender lymphadenopathy (especially posterior cervical; often called "tender glands") and splenomegaly
.
, rubella
, lymphoma
and leukemia
.
However, the sensitivity is only moderate, so a negative test does not exclude EBV. This lack of sensitivity is especially the case in young children, many of whom will not produce the heterophile antibody at any stage and thus have a false negative test result.
In the case of delayed or absent seroconversion
, an immunofluorescence test could be used if the diagnosis is in doubt. It has the following characteristics: VCAs (Viral Capsid Antigen) of the IgM class, antibodies to EBV early antigen (anti-EA), absent antibodies to EBV nuclear antigen (anti-EBNA)
Heterophile
Heterophile is an alternate term to heterosexual and once competed with it for currency, but only did so successfully in Scandinavia. It is a parallel concept to homophile....
antibodies produced by the human immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
in response to EBV infection.
The monospot test, a form of the heterophile antibody test, is a rapid test for infectious mononucleosis
Infectious mononucleosis
Infectious mononucleosis is an infectious, widespread viral...
due to Epstein–Barr virus (EBV). Commercially-available test kits are 70-92% sensitive
Sensitivity and specificity
Sensitivity and specificity are statistical measures of the performance of a binary classification test, also known in statistics as classification function. Sensitivity measures the proportion of actual positives which are correctly identified as such Sensitivity and specificity are statistical...
and 96-100% specific
Sensitivity and specificity
Sensitivity and specificity are statistical measures of the performance of a binary classification test, also known in statistics as classification function. Sensitivity measures the proportion of actual positives which are correctly identified as such Sensitivity and specificity are statistical...
. It will generally not be positive during the 4-6 week incubation period before the onset of symptoms. It will also not generally be positive after active infection has subsided, even though the virus persists in the same cells in the body for the rest of the carrier's life.
Process
The test relies on the agglutination of horse RBCs by heterophile antibodies in patient's serum. Heterophile means it reacts with proteins across species lines.A 20% suspension of horse red cells is used in an isotonic 3-8 % sodium citrate formulation.
One drop of the patient’s serum to be tested is mixed on an opal glass slide with one drop of a particulate suspension of guinea-pig kidney stroma, and a suspension of beef red cell stroma; sera and suspensions are mixed with a wooden applicator for 10 times.
Ten micro liter of the horse red cell suspension are then added and mixed with each drop of absorbed serum.
The mixture is left undisturbed for one minute (not rocked or shaken).
Examine for the presence or absence of red cell agglutination.
If stronger with the sera absorbed with guinea-pig kidney, the test is positive.
If stronger with the sera absorbed with beef red cell stroma, the test is negative.
If agglutination is absent in both mixtures, the test is negative.
A known 'positive' and 'negative' control serum is tested with each batch of test sera.
Indications
It is indicated as a confirmatory test when a physician suspects EBVEBV
EBV may refer to:* Epstein-Barr virus, a virus of the herpes family* EBV infectious mononucleosis, mononucleosis caused by the Epstein-Barr virus* Escuela Bella Vista, an American school located in Maracaibo, Venezuela...
, typically in the presence of clinical features such as fever, malaise, pharyngitis, tender lymphadenopathy (especially posterior cervical; often called "tender glands") and splenomegaly
Splenomegaly
Splenomegaly is an enlargement of the spleen. The spleen usually lies in the left upper quadrant of the human abdomen. It is one of the four cardinal signs of hypersplenism, some reduction in the number of circulating blood cells affecting granulocytes, erythrocytes or platelets in any...
.
Usefulness of the test
The specificity of the test is high, virtually 100%, so a positive test is useful in confirming EBV. Rarely, however, a false positive heterophile antibody test test may result from toxoplasmosisToxoplasmosis
Toxoplasmosis is a parasitic disease caused by the protozoan Toxoplasma gondii. The parasite infects most genera of warm-blooded animals, including humans, but the primary host is the felid family. Animals are infected by eating infected meat, by ingestion of feces of a cat that has itself...
, rubella
Rubella
Rubella, commonly known as German measles, is a disease caused by the rubella virus. The name "rubella" is derived from the Latin, meaning little red. Rubella is also known as German measles because the disease was first described by German physicians in the mid-eighteenth century. This disease is...
, lymphoma
Lymphoma
Lymphoma is a cancer in the lymphatic cells of the immune system. Typically, lymphomas present as a solid tumor of lymphoid cells. Treatment might involve chemotherapy and in some cases radiotherapy and/or bone marrow transplantation, and can be curable depending on the histology, type, and stage...
and leukemia
Leukemia
Leukemia or leukaemia is a type of cancer of the blood or bone marrow characterized by an abnormal increase of immature white blood cells called "blasts". Leukemia is a broad term covering a spectrum of diseases...
.
However, the sensitivity is only moderate, so a negative test does not exclude EBV. This lack of sensitivity is especially the case in young children, many of whom will not produce the heterophile antibody at any stage and thus have a false negative test result.
In the case of delayed or absent seroconversion
Seroconversion
Seroconversion is the development of detectable specific antibodies to microorganisms in the blood serum as a result of infection or immunization. Serology is used to determine antibody positivity...
, an immunofluorescence test could be used if the diagnosis is in doubt. It has the following characteristics: VCAs (Viral Capsid Antigen) of the IgM class, antibodies to EBV early antigen (anti-EA), absent antibodies to EBV nuclear antigen (anti-EBNA)