Immulite 2000 parathyroid hormone assay: stability of parathyroid hormone in EDTA blood kept at room temperature for 48 h

Abstract

SUMMARY. Parathyroid hormone (PTH) concentrations were compared in serum and EDTA plasma from 36 patients attending a renal stone clinic. Serum PTH concentrations ranged from 0·9 to 10·9pmol/L, with a mean of 4·6 pmoljL. When serum and EDT A plasma results were compared, in samples frozen within 30min of collection, EDTA plasma results were found to be significantly higher than those in serum (P<O·OOOI; Wilcoxon test), with an average increase of 19·5% over the serum result. Results from EDT A-preserved blood left to stand at room temperature for 48 h were on average 14·8% lower than results from the corresponding EDTA plasma samples frozen within 30 min, with a highly significant difference (P<O·OOOI). Freshly frozen serum and 48h EDTA plasma PTH results were not significantly different.Parathyroid hormone in EDT A-preserved blood is not completely stable, and this could lead to misclassification of results for samples which are not frozen quickly.Parathyroid hormone (PTH) has a half-life of approximately 5 min in the circulation and is unstable in whole blood or serum.

Influence of Preanalytical Factors on the Immulite Intact Parathyroid Hormone Assay

“…The results presented here confirm previous reports describing higher apparent PTH concentrations in EDTA plasma than in serum (1,2 ) and changes in PTH concentrations with time (1)(2)(3)(4)(5)(6). In agreement with what has been published for the DPC PTH assay (1 ), we found a slight increase in PTH concentration in EDTA plasma with time.…”

“…Measured PTH concentrations in EDTA plasma may (1,2 ) or may not (3 ) differ from those in serum. PTH has been reported variously to be stable for hours to days (1)(2)(3)(4)(5)(6). In addition, different PTH assays cross-react to various extents with biologically inactive, N-terminally truncated PTH molecules (7 ) that may have different stabilities.…”

Stability of parathyroid hormone ex vivo in haemodialysis patients

“…The two studies using Immulite 2000 6,7 both showed PTH to be higher in EDTA plasma than serum at baseline, whereas our study and that of Levin and Nisbet showed PTH to be slightly lower. There may have also been subtle di¡erences in sample handling and preparation.…”

“…After 3 days of storage, measured PTH concentration in EDTA plasma had not decreased, but had declined by more than 40% in serum. Omar et al, 7 using the Immulite 2000, also observed improved stability in EDTA plasma. However, in their study, PTH concentrations in fresh EDTA plasma were 20% higher than in fresh serum.…”

Sampling and storage conditions influencing the measurement of parathyroid hormone in blood samples: a systematic review

“…Fifteen papers relating to PTH stability in whole blood were identified that had used a second generation assay ( Figure 2, Supplemental Data Table 3) [15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. Collation of study results was difficult due to variation in experimental design (see above), but almost all studies suggested that PTH was more stable in whole blood samples containing EDTA than in anticoagulant-free samples (Supplemental Data Table 3).…”