The Stability of Intact Parathyroid Hormone (PTH) in Different Types of Blood Collection Tubes.

BACKGROUND

Over past decades, the instability of parathyroid hormone (PTH) causes great interference for the clinical laboratory. Contradictory results were reported in many reports about storage conditions and suitable blood collection tubes to ensure PTH stability in the pretreatment phase.

METHODS

This study recruited 30 participants including 10 healthy persons, 10 hemodialysis, and 10 hyperparathyroidism patients. Five types of blood collection tubes (EDTA-K3 tube, coagulant tube, heparin anticoagulant tube, gel separating tube, and plain tube) were included to determine whether they were suitable as blood-collecting vessels. The time points and conditions for testing samples included less than 2 hours, 4 hours, and 8 hours at room temperature, and, in parallel, 24 hours, 48 hours, and 72 hours in refrigeration. Two different judgement criteria were used to compare the stability of PTH in different blood vessels.

RESULTS

Purely statistical analysis showed that 4 types of blood collection tubes could not perform the same storage ability as EDTA-K3 tube at "T0" time point. Plain tube had the largest drop among all types of blood collection tubes. Compared by pairwise t-test, EDTA-K3 tube could maintain intact PTH for 8 hours (p = 0.998) at room temperature and 24 hours (p = 0.053) in refrigeration. When comparing the total change limit (TCL = 18.8%), at room temperature, EDTA-K3 tube (7.0%), heparin tube (12.7%), coagulant tube (16.2%), and plain tube (17.6%) could maintain intact PTH for 8 hours, and GST can preserve PTH for 4 hours (18.2%). In refrigeration, EDTA-K3 tube could maintain PTH for 72 hours (7.5%) and heparin tube could maintain 24 hours (18.4%). The other three blood collection tubes could not preserve PTH in refrigeration (GST = 22.1%, coagulant tube = 20.3%, plain tube = 20.8%).

CONCLUSIONS

PTH seems more stable in the EDTA-K3 tube than any other blood collection tubes and is followed next by the heparin anticoagulant tube. Plain tube and GST have faster degradation than other tubes and are not suggested to preserve intact PTH.