PTH bioactivity in osteoporosis.

The cytochemical bioassay for parathyroid hormone was used to measure the levels of PTH bioactivity in normal elderly subjects and patients suffering from idiopathic or postmenopausal osteoporosis. In normal subjects, PTH bioactivity did not increase with age. In the osteoporotic patients levels of bioPTH discriminated between two populations, one with normal levels and the other with elevated levels. In both these groups the PTH bioactivity was neutralised by the addition of a PTH antiserum. The recovery of the bioactivity of PTH added to the plasma samples was significantly higher in the plasmas from patients with elevated levels of bioPTH. Levels of immunoreactive PTH also discriminated between the two groups of osteoporotic patient although no serum parameters indicative of increased PTH were detectable. However, patients with the high levels of bio- and immunoPTH had a lower incidence of fracture within the previous 12 months.