Endocrine Abstracts

Introduction: ‘Primary Aldosteronism Detection, Diagnosis and Treatment Guidelines’ from the Endocrine Society (2008) recommend the use of the aldosterone- renin ratio (ARR) to detect primary aldosteronism (PA) in patient groups with high prevalence of PA. The guidelines suggest cut-offs specific to assay type and measurement units. The department of Clinical Chemistry and Metabolic Medicine at RLBUHT recently moved to a direct renin method (iSYS, Immunodiagnostics) and the calculated ARR and aldosterone measurement (iSYS, Immunodiagnostics) was evaluated for routine reporting in patients investigated for PA.

Method: 74 patient samples were measured by direct renin assay. 43 patient samples were eligible for inclusion in the evaluation after those with non-numerical results and no concurrent aldosterone results were excluded. The concurrent aldosterone result was taken for each patient from the laboratory information management system (Telepath, iSOFT) and the ARR determined. Clinical information for each patient sample was also collected. Samples were split into categories determined by the method specific cut-off values for ARR and aldosterone (from Immunodiagnostics).

Results: 32 samples were categorised as ‘PA unlikely’, (ARR <30 pmol/mIU). Eight samples were categorised as ‘Consistent with PA (confirmatory testing suggested)’, (ARR >30 pmol/mIU, aldosterone >400 pmol/l). Three samples were categorised as ‘PA not excluded’, (ARR >30 pmol/mIU, aldosterone 250–400 pmol/l). No samples were categorised as ‘PA unlikely (aldosterone not in range associated with PA)’, (ARR >30 pmol/mIU, aldosterone <250 pmol/l). Mean ARR =29 pmol/mIU, median=49 pmol/mIU for all samples (range =1–279 pmol/mIU). All samples had appropriate clinical details including ‘hypertension’, and ‘adrenal lesion’.

Conclusion: The selected cut-off values for ARR appear appropriate for use although we were unable follow up patients and thus cannot determine sensitivity/specificity. Most samples had a normal ARR of <30 pmol/mIU. Clinical information indicates that most requests are appropriate in reference to the guidelines.