Endocrine Abstracts

Approximately 70% of clinical laboratories in the United Kingdom use assays from Abbott Laboratories and Roche Diagnostics. We carried out a cross-sectional study between two neighbouring hospital laboratories in our regional pathology network, comparing the potential impact of Abbott and Roche PTH and calcium assays in the diagnosis of normocalcaemic hyperparathyroidism. Over 4 months, forty-one vitamin D replete (>50 nmol/l) normocalcaemic hyperparathyroidism patients (37 females, median age 69 years, IQR 63-77) with eGFR >60 ml/min/1.73m² were identified using the Abbott assays. The serum samples were aliquoted and stored at -80°C soon following the conclusion of requested tests, maximally within 8 h of receipt. Aliquots were thawed and analysed immediately by Abbott and Roche assays within one month of storage. Abbott PTH results were 57.6% (IQR 49.4-74.7) higher compared to Roche PTH results (P < 0.001). Roche adjusted calcium results were 3.8% (IQR 2.4-5.3) higher compared to Abbott adjusted calcium results (P < 0.001). Of the 41 patients with normocalcaemic hyperparathyroidism by the Abbott assays, 22 (54%) had a normal PTH and adjusted calcium and 9 (22%) had results indicative of primary hyperparathyroidism when measured by Roche assays. Only 10 (24%) patients were concordant for normocalcaemic hyperparathyroidism by both assays. The manufacturer-provided assay-specific reference ranges used by the laboratories for Abbott and Roche PTH assays are similar at 1.6-7.2 pmol/l and 1.9-6.9 pmol/l respectively; however, Abbott PTH assays have a considerable positive bias compared to Roche PTH assays. The laboratories use the pathology harmony adjusted calcium reference range of 2.2-2.6 mmol/l; however, Abbott calcium assay has a 3.8% (median 0.09 mmol/l) negative bias compared to Roche calcium assay. In conclusion, the diagnosis of normocalcaemic hyperparathyroidism is strikingly different depending upon the assays used, highlighting a need for harmonisation and consideration of assay related factors in clinical practice.