Endocrine Abstracts

Concerns on the noncomparibility of intact parathyroid hormone (iPTH) methods have recently been voiced (Cantor T et al; Clin Chem 2006, 52, 1771–6). It is therefore important that any new iPTH immunoassays are thoroughly validated before routine use. We describe performance characteristics for an iPTH immunoassay on the ARCHITECT 8200i analyser as compared with iPTH measurement on the Diasorin LIAISON platform. Potassium EDTA plasma samples (n=80) were selected from our routine workload across the analytical working range. External quality assessment samples provided by NEQAS (n=18) were also included. The ARCHITECT results were significantly higher than the LIAISON method (y=0.4x+16, R²=0.798). Precision of the ARCHITECT method was acceptable with CVs of 3.8%, 3.8%, 6.0% and 4.8% respectively at PTH concentrations of 2.8, 5.6, 13.6 and 43 pmol/l. The minimum detection limit, as assessed by multireplicate analysis of hormone free serum, was 0.04 pmol/l. Recovery of PTH 1–84 (Peninsula Laboratories) spiked at 3 concentrations into 5 samples with varying basal iPTH concentrations showed significant over-recovery (mean 153%, range 139%–190%) although samples showed linear dilution. A provisional reference range for the Abbott method was established on 50 healthy normocalcaemic laboratory volunteers (age range 21–59 yrs) and found to be 1.3–9.2 pmol/l.

The Abbott ARCHITECT iPTH method shows acceptable precision, working range and minimum detection limit. There is, however, significant over-recovery and an increase in reference range compared to that obtained by Diasorin LIAISON method. Samples from well categorised clinical groups e.g. primary hyperparathyroidism, hypoparathyroidism and hypercalcaemia of malignancy are being collected to establish the clinical suitability of this new method.