Challenges of PTH Assays

Parathyroid hormone (PTH) plays a vital role in regulating of blood Calcium. In addition, it regulates the amount of phosphate and vitamin D in the blood. PTH is a polypeptide hormone that found in the blood circulation as peptides with different amino acid counts. The active form of the PTH which has biological activity, contains 84 amino acids, but under the influence of proteolytic enzymes, fragments of this major molecule are broken down and found in the bloodstream. Therefore smaller fragments (derived peptides) don’t have biological activity but have antigenic properties and can be detected in radioimmunoassay with i-PTH and may affected the results of test. Over the 50 years since the invention of the first generation of PTH assays, PTH assay techniques have evolved a great deal. The first generation of PTH measurement kits used polyclonal antibodies from animals. In those kits, in addition to i-PTH , other fragments were also detected. However, gradually subsequent generation of kits have been invented that have been able to detect only the active form(i-PTH) using monoclonal antibodies. In addition, since PTH is very unstable, compliance with preanalytical conditions is extremely important.