Endocrine Abstracts

Background: Confirmatory tests, including saline infusion test (SIT), captopril challenge test (CCT) and fludrocortisone suppression test (FST) are commonly used for diagnosis of primary aldosteronism (PA). Each test has its advantages and disadvantages, but which one should be preferentially performed is controversial. We aimed to evaluate the diagnostic accuracy of three tests in a prospective study.

Methods: Five hundred and thirty-one hypertensive patients with high risk of PA were enrolled. Plasma aldosterone-renin ratio (ARR) was used for screening. Hypertensive patients tested positive at PA screening (ARR≥3.7 ng/dl per μIU/ml), one in every three consecutive patient tested negative (ARR<3.7 ng/dl per μIU/ml) and patients who tested negative but PA was strongly suspected proceeded to three confirmatory tests. Area under receiver operator characteristics curve (AUC), sensitivity and specificity were calculated. A systematic review and meta-analysis of relevant studies were performed to place our results in context.

Findings: Finally, 132 patients diagnosed as PA and 104 diagnosed as essential hypertension completed three tests. AUC of CCT, SIT and FST were 0.97 (95% CI 0.95–0.99), 0.97 (0.95–0.99) and 0.98 (0.97–0.99), respectively, when post-test plasma aldosterone concentration (PAC) was used to confirm PA. But AUC of CCT significantly decreased to 0.76 (0.69–0.82) if PAC suppression ratio was used to confirm PA. When PAC cutoffs of SIT and FST was set at 8 ng/dl, and CCT at 11 ng/dl, the sensitivity were 87.9%, 93.2%, 92.4% and specificity were 93.3%, 90.4%, 90.4% respectively. No significant difference of synthetic AUC, pooled sensitivity or specificity between SIT and CCT was found in the meta-analysis. Only one study of FST fulfilling the criteria of the systematic review was included, reporting a sensitivity of 0.87 and a specificity of 0.95.

Interpretation: CCT, SIT and FST has comparable diagnostic accuracy. Based on their pros and cons, it is reasonable to recommend CCT as the first choice to confirm PA in clinical practice. When interpreting the results of CCT, PAC post-CCT is recommended.