Procalcitonin ELISA
The Human Procalcitonin ELISA is a sandwich enzyme immunoassay for measurement of human procalcitonin.
Procalcitonin (PCT) the precursor of the hormone calcitonin, is a 116 amino acid protein with a molecular mass of 13 kDa. It undergoes successive cleavages in the neuroendocrine cells of the thyroid to form three distinct molecules; calcitonin (32 amino acids); katacalcin (21 amino acids) and N-terminal fragment called aminoprocalcitonin (57 amino acids). Procalcitonin belongs to a group of related proteins including calcitonin gene-related peptides I and II, amylin, adrenomodulin and calcitonin (CAPA peptide family). Synthesis of procalcitonin is regulated gene CALC-1. Under normal metabolic conditions procalcitonin is present in the C-cells of the thyroid gland. The level of procalcitonin in the blood of healthy individuals is low. The risk of local bacterial infection occurs when the value of procalcitonin exceeds 0.25 ng/ml. The risk of systemic bacterial infection occurs when the value of procalcitonin exceeds 0.5 ng/ml. Bacterial lipopolysacharide (LPS) has been shown to be a potent inducer of procalcitonin release into systemic circulation. This release is not associated with an increase in calcitonin. Procalcitonin levels increase from 3 to 4 hours, peak at about 6 hours and then plateau for up to 24 hours. In contrast, C-reactive protein (CRP) levels rise between 12 and 18 hours after bacterial challenge. In blood serum, procalcitonin has a half-life of between 25 and 30 hours. A study showed that hepatocytes produce large amounts of procalcitonin following stimulation with TNF-α and IL-6. In acute pancreatitis, procalcitonin closely correlates with the development of pancreatic infections.
In the Human Procalcitonin ELISA, standards, quality controls and samples are incubated in microplate wells pre-coated with polyclonal anti-human procalcitonin antibody. After 120 minutes incubation and washing, biotin labelled polyclonal anti-human procalcitonin antibody is added and incubated with captured procalcitonin for 60 minutes. After another washing, streptavidin-HRP conjugate is added. After 30 minutes incubation and the last washing step, the remaining conjugate is allowed to react with the substrate solution (TMB). The reaction is stopped by addition of acidic solution and absorbance of the resulting yellow product is measured. The absorbance is proportional to the concentration of procalcitonin. A standard curve is constructed by plotting absorbance values versus procalcitonin concentrations of standards, and concentrations of unknown samples are determined using this standard curve.
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