Endocrine Abstracts

We report an interference in an immunoassay for aldosterone, which potentially could have led to a wrongful diagnosis and unnecessary surgery. The interference was serendipitously recognized due to a preanalytical error. A 59-year-old female patient with hypertension was referred to the department of endocrinology after an adrenal incidentaloma was detected. Because of her hypertensive history, screening for primary hyperaldosteronism was performed. An elevated aldosterone and a raised aldosterone/renin ratio was measured. To confirm the diagnosis of primary hyperaldosteronism a saline infusion test was performed. However, Aldosterone could not be reliably measured by our own immunoassay (Liaison XL) due to hemolysis in the sample taken after 2L saline infusion. This sample, together with the sample before infusion, was sent to our referral laboratory, where aldosterone was measured by LC–MS/MS. Low concentrations of aldosterone were measured by LC–MS/MS in both samples, rejecting the diagnosis hyperaldosteronism. Strikingly, the basal aldosterone concentration as measured by LC–MS/MS was much lower comparted to the concentration as measured by the Liaison XL immunoassay, raising suspicion of an assay interference. Confirmative testing with a repeat sample, using an additional immunoassay (Lumipulse 2100) and a dilution experiment all pointed towards a method specific interference in our own immunoassay. These results showed that the patient did not have primary hyperaldosteronism and that her incidentaloma was hormonally inactive. In retrospect, based on these results dynamic testing would not have been necessary. Surgical intervention was not performed and the patient was treated with antihypertensive drugs. Since in most laboratories aldosteron results from both screening and confirmative tests are derived from the same method, analytical interference in an immunoassay is difficult to detect. This especially holds true if there is a high clinical probability for primary hyperaldosteronism as in this case due to presence of hypertension and the finding of an adrenal incidentaloma. This may also explain the low number of publications on this type of interference in the literature.