Preliminary studies with the sensitive cytochemical assay for parathyroid hormone

A modification of the cytochemical assay for parathyroid hormone (PTH) is described which permits the measurement of as little as 0.1 fg ml-1. Using this assay circulating concentrations in normal humans range between 1 and 30 pg ml-1 using a bovine PTH standard. Elevated values are found in hyperparathyroidism with reduced concentrations in hypoparathyroidism. Where detectable, PTH concentrations measured by radioimmunoassay are on average fourteen-fold higher than by cytochemical assay. No cross reactivity was found with AVP, calcitonin and 1,25 dihydroxy vitamin D in concentrations normally found in health or disease.