اختبار PTH

Calcium is not merely a structural component of bone; it is an essential signalling ion that controls muscle contraction, nerve impulse transmission, hormone secretion, blood clotting, and intracellular signalling. Maintaining serum ionised calcium within a narrow range of approximately 1.15 to 1.35 mmol/L is therefore a physiological imperative. The parathyroid calcium-sensing receptor (CaSR), a G-protein coupled receptor on the surface of parathyroid chief cells, monitors ionised calcium concentrations in real time and modulates PTH secretion within seconds. This exquisitely sensitive feedback system means that PTH levels change dynamically throughout the day in response to dietary calcium intake, and mild sustained disruptions to this axis carry significant long-term consequences for bone, kidney, and cardiovascular health.

Laboratory measurement of PTH has evolved significantly. First-generation PTH assays measured fragments including biologically inactive C-terminal fragments that accumulate in kidney disease, causing significant overestimation in renal patients. Second-generation intact PTH assays (iPTH) measure only the full-length 1-84 amino acid molecule alongside larger fragments, offering superior accuracy in most clinical contexts. Third-generation "biointegral" or "whole" PTH assays that measure only the complete 1-84 molecule are available for research and specific clinical situations including intraoperative PTH monitoring during parathyroidectomy, where a greater than 50 percent decline in PTH within 10 minutes of adenoma removal confirms successful surgical cure.