Parathyroid Hormone Is More Stable in EDTA Plasma Than in Serum

Abstract

Measurements of circulating parathyroid hormone (PTH) are important in the evaluation of individuals with hyper- or hypocalcemia and for the investigation of PTH function in bone and mineral disorders (1)(2). Serum may be a good alternative to EDTA plasma in the assessment of PTH status and is an acceptable alternative to EDTA plasma in the reformulated IMMULITE 2000 intact PTH (iPTH) assay. However, reports on the stability of PTH in serum and EDTA plasma are conflicting (3)(4)(5). Blood samples from 36 patients were collected in parallel into 10-mL tripotassium EDTA tubes, ensuring complete sample filling of the collection vessel (6), and into Becton Dickinson SST II gel separator tubes. PTH was assayed with the reformulated IMMULITE 2000 iPTH assay (beginning with lot L2KPP 106) within 3 h of collection and reassayed on both samples after storage for 3 days at room temperature. The mean iPTH was 14.8 pmol/L (range, 0.9–27 …