Context: Both saline infusion test (SIT) and the captopril challenge test (CCT) are accurate alternatives to the fludrocortisone suppression test (FST), which is generally accepted as a reliable but cumbersome confirmatory test in primary aldosteronism (PA). The combination of two independent diagnostic tests gets a higher accuracy in some diseases. However, whether a combination of CCT and SIT could improve the diagnostic accuracy of PA is still unknown.
Objective: To evaluate the diagnostic accuracy for a combination of CCT and SIT in PA diagnosis.
Methods: This study is an extension of Chongqing Primary Aldosteronism Study (CONPASS), which is a prospective study with some published results. We retrospectively recruited 164 patients with PA and 116 patients with essential hypertension (EH) who had completed FST, CCT and SIT. The post-test plasma aldosterone concentration (PAC) was used for the three confirmatory tests. The reference standard was FST, and the cut-off was set at 8 ng/dL. The index tests were CCT, SIT and a combination of CCT and SIT. Area under receiver operator characteristics curve (AUC), sensitivity and specificity were calculated.
Results: AUCs for CCT, SIT and a combination of CCT and SIT were 0.94(95% CI 0.91, 0.97), 0.95(0.91, 0.98) and 0.96(0.92, 0.98) respectively (P =0.204 for CCT vs. combination; P= 0.512 for SIT vs. combination). When the optimal cutoff of PAC post-CCT was set at 8 ng/dL and PAC post-SIT at 11 ng/dL, the sensitivity for CCT and SIT was 0.87 and 0.86 respectively, and the specificity for CCT and SIT was 0.91 and 0.92 respectively. A combination of CCT and SIT generated a sensitivity of 0.86 and a specificity of 0.92. Neither sensitivity nor specificity of the combination was significantly different from CCT or SIT.
Conclusion:. A combination of CCT and SIT does not improve the diagnostic accuracy of primary aldosteronism.