Procalcitonin is a peptide

Peptide

Peptides are short polymers of amino acid monomers linked by peptide bonds. They are distinguished from proteins on the basis of size, typically containing less than 50 monomer units. The shortest peptides are dipeptides, consisting of two amino acids joined by a single peptide bond...

 precursor

Protein precursor

A protein precursor, also called a pro-protein or pro-peptide, is an inactive protein that can be turned into an active form by posttranslational modification. The name of the precursor for a protein is often prefixed by pro...

 of the hormone calcitonin

Calcitonin

Calcitonin is a 32-amino acid linear polypeptide hormone that is producedin humans primarily by the parafollicular cells of the thyroid, and in many other animals in the ultimobranchial body. It acts to reduce blood calcium , opposing the effects of parathyroid hormone . Calcitonin has been found...

, the latter being involved with 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...

 homeostasis

Homeostasis

Homeostasis is the property of a system that regulates its internal environment and tends to maintain a stable, constant condition of properties like temperature or pH...

. It is composed of 116 amino acid

Amino acid

Amino acids are molecules containing an amine group, a carboxylic acid group and a side-chain that varies between different amino acids. The key elements of an amino acid are carbon, hydrogen, oxygen, and nitrogen...

s and is produced by parafollicular cell

Parafollicular cell

Parafollicular cells are cells in the thyroid that produce and secrete calcitonin. They are located adjacent to the thyroid follicles and reside in the connective tissue. These cells are large and have a pale stain compared with the follicular cells or colloid...

s (C cells) of the thyroid

Thyroid

The thyroid gland or simply, the thyroid , in vertebrate anatomy, is one of the largest endocrine glands. The thyroid gland is found in the neck, below the thyroid cartilage...

 and by the neuroendocrine cell

Neuroendocrine cell

Neuroendocrine cells are cells that receive neuronal input and, as a consequence of this input, release message molecules to the blood. In this way they bring about an integration between the nervous system and the endocrine system, a process known as neuroendocrine integration...

s of the lung and the intestine.

The level of procalcitonin in the blood stream of healthy individuals is below the limit of detection (10 pg/mL) of clinical assays. The level of procalcitonin raises in a response to a proinflammatory stimulus, especially of bacterial origin. In this case, it is produced mainly by the cells of the lung and the intestine. It does not raise significantly with viral or non-infectious inflammations. With the derangements that a severe infection

Infection

An infection is the colonization of a host organism by parasite species. Infecting parasites seek to use the host's resources to reproduce, often resulting in disease...

 with an associated systemic response brings, the blood levels of procalcitonin may rise to 100 ng/ml. In serum, procalcitonin has a half-life of 25 to 30 hours. Remarkably the high procalcitonin levels produced during infections are not followed by a parallel increase in calcitonin or serum calcium levels.

Diagnosis and prognosis of sepsis

Measurement of procalcitonin can be used as a marker of severe 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...

 and generally grades well with the degree of sepsis, although levels of procalcitonin in the 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....

 are very low. PCT has the greatest sensitivity (85%) and specificity (91%) for differentiating patients with SIRS from those with sepsis, when compared with IL-2

Interleukin 2

Interleukin-2 is an interleukin, a type of cytokine immune system signaling molecule, which is a leukocytotrophic hormone that is instrumental in the body's natural response to microbial infection and in discriminating between foreign and self...

, IL-6

Interleukin 6

Interleukin-6 is a protein that in humans is encoded by the IL6 gene.IL-6 is an interleukin that acts as both a pro-inflammatory and anti-inflammatory cytokine. It is secreted by T cells and macrophages to stimulate immune response, e.g. during infection and after trauma, especially burns or other...

, IL-8

IL-8

IL-8 can refer to:* Interleukin 8, a chemokine of the immune system* Illinois' 8th congressional district* Illinois Route 8...

, CRP

C-reactive protein

C-reactive protein is a protein found in the blood, the levels of which rise in response to inflammation...

 and TNF-alpha. Evidence is emerging that procalcitonin levels can reduce unnecessary antibiotic prescribing to people with lower respiratory tract infection

Lower respiratory tract infection

Lower respiratory tract infection while often used as a synonym for pneumonia, can also be applied to other types of infection including lung abscess and acute bronchitis...

s. Currently, procalcitonin assays are widely used in the clinical environment.

Diagnosis of bacteremia

A meta-analysis reported a sensitivity of 76% and specificity of 70%.

Prognosis of pneumonia

A cluster randomized trial found that the procalcitonin level can help guide antibiotic therapy. In this trial, "on the basis of serum procalcitonin concentrations, use of antibiotics was more or less discouraged (<0.1 mcg/L or <0.25 mcg/L) or encouraged (> or =0.5 mcg/L or > or =0.25 mcg/L), respectively". However, an earlier nonrandomized, observational study reported "limited, prognostic value" of procalcitonin measurement.

Procalcitonin levels may be useful to distinguish bacterial infections from nonbacterial infections. Trials from 2008 and 2009 have shown that they may help guide therapy and reduce antibiotic use, which can help save on cost of antibiotic prescriptions and drug resistance.

External links

• Procalcitonin - web site of the manufacturer of the PCT assay.