Endocrine Abstracts

Background: Primary aldosteronism is an increasingly recognised cause of hypertension, caused by excess aldosterone secretion. Screening and confirmatory tests such as saline suppression tests (SST) require accurate measurements of aldosterone and use of appropriate cut-offs. Many laboratories have chosen liquid chromatography tandem mass spectrometry (LC-MSMS) methods as issues of poor specificity have been reported for immunoassay methods. During the validation of a LC-MSMS method at Glasgow Royal Infirmary (GRI), comparison with the existing IDS-iSYS immunoassay showed a 35% negative bias, requiring re-evaluation of the aldosterone renin ratio and SST cut-offs.

Method: Paired specimens from SST (n=55) referred to GRI for aldosterone were analysed by immunoassay (IDS-iSYS) and LC-MSMS methods. Samples with baseline Aldo_LC-MSMS > 210 pmol/l (equivalent to Aldo_IA 300 pmol/l) were excluded. Clinical information was obtained for all patients. Interpretation of SST varies between centres but several studies quote an immunoassay aldosterone (Aldo_IA) of < 190 pmol/l as an appropriate response. From sample comparison Aldo_IA =190 pmol/l equates to Aldo_LC-MSMS =120 pmol/l.

Results: Concordant results were recorded for 37/42 patients and 5/42 were discrepant. Two patients had potential false positives by IA resulting in unnecessary investigations. Three patients were potentially false negatives by IA, all of which required alterations to their medical management. One of these patients also had a false negative Aldo_IA baseline result. An additional patient not included as the baseline Aldo_LC-MSMS=174 pmol/l, underwent unnecessary adrenal vein sampling due to possible false positive IA results, pre and post SST.

Conclusion: This data highlights the variability in performance of the immunoassay method compared to the LC-MSMS method. Unfortunately definitive outcomes were not available for the patients in this cohort but potential false positive and false negative results were reported. False positive confirmatory tests put the patient at risk of unnecessary invasive procedures such as adrenal vein sampling.