PTH

DESCRIPTION:
PTH is a single-chain peptide hormone with a molecular weight of 9425 daltons and consists of 84 amino acids. The amino acids (1 to 27) of the N-terminal portion of the hormone molecule are responsible for biological activity. The biological half-life of intact PTH is approximately 4 minutes. In vitro stability of PTH is limited. In vivo, PTH is rapidly cleaved in the liver and kidneys into various fragments. Only the N-terminal amino acids 1–34 are required for biological activity (receptor binding). C-terminal fragments apparently have no biological role, but circulate longer in plasma than N-terminal fragments. Therefore, a better parameter for assessing parathyroid gland status is the determination of intact PTH molecule. Blood contains a mixture of intact PTH and various fragments. Specific determination of intact PTH is possible using sandwich immunoassay technique in which one antibody acts (binds) on the N-terminal portion of amino acids 1–34, while another antibody reacts with the C-terminal portion.

DETERMINATION:
The determination method is CMIA. The sample is stable for 2 days at 2-8°C, at -20°C for 6 months. The sample for analysis is plasma (EDTA only!).

RESULTS:
Reference interval: 1.6–6.9 mmol/L