STABILITY OF PARATHYROID HORMONE-RELATED PROTEIN AND PARATHYROID-HORMONE AT ROOM-TEMPERATURE

The stability of plasma parathyroid hormone-related protein (PTHrP) as measured by the Nichols Institute assay at room temperature was asses sed over a period of 72 h in blood samples collected in protease inhib itor tubes and EDTA tubes at 0, 6, 24, 48 and 72 h from 10 patients wi th hypercalcaemia of malignancy. Mean plasma PTHrP concentrations in b lood samples collected in protease inhibitor tubes remained stable for up to 48 h but had decreased by 10% at 72 h. The mean EDTA plasma PTH rP at zero time was 67% of the protease inhibitor tube value and this had fallen to 39% at 72 h. The stability of parathyroid hormone (PTH) in separated blood samples was also assessed by collection into hepari n and plain tubes as well as EDTA and protease inhibitor tubes. Serum PTH concentrations progressively declined throughout the 72 h study pe riod although the zero time values were significantly higher than corr esponding plasma PTH concentrations. Plasma PTH concentrations appeare d to be stable when blood was collected in heparin, EDTA and protease inhibitor tubes during the 72 h period, except in one subject with mar kedly elevated plasma amylase activity.