The effect of potassium EDTA on the stability of parathyroid hormone in whole blood

Abstract

The stability of parathyroid hormone (PTH) in whole blood has not been well characterized. Previous studies show EDTA plasma samples to be more stable than serum samples. Blood from 17 haemodialysis patients and five healthy volunteers was collected into serum separator tubes (SSTs) and potassium EDTA tubes (EDTA-Ts) and incubated at room temperature before separation and storage for PTH analysis using the Bayer Advia Centaur. Initial PTH concentrations were 7% higher (95% confidence interval [CI] 2-16%, P=0.016) in EDTA-Ts compared to the SSTs in the renal cohort. PTH concentrations in SSTs were significantly lower after 8 (10%, 95% CI 3-17%) and 20 h (22%, 95% CI 11-31%) but did not change significantly in EDTA-Ts (P=0.1543). PTH concentration in EDTA-Ts from healthy volunteers was also independent of incubation time (P=0.1165). The greater stability of PTH in whole blood anticoagulated with potassium EDTA allows PTH analysis to be offered to sites such as satellite clinics and primary care sites which do not have centrifugation and refrigeration facilities.