Endocrine Abstracts

Objective: To evaluate the optimal parameters and the cut-off points of captopril challenge test (CCT) in the diagnosis of primary aldosteronism (PA) using chemiluminescence immunoassays (CLIA).

Methods: Patients with clinically suspected PA who admitted to our hospital between July 2021 and December 2021 were recruited. Both supine and upright aldosterone to renin ratio (ARR) were calculated in all the participants and 21 healthy volunteers. CCT was performed in all those ARR≥25 and the first two out of three ARR<25. Blood samples were drawn before, 1 h and 2 h after oral 50mg captopril for the measurements of plasma renin concentration (PRC) and plasma aldosterone concentration (PAC). PRC was measured by CLIA while PAC was measured by both CLIA and liquid chromatography-mass spectrometric (LC-MS/MS). ARR before CCT, at 1 h post-CCT and 2 h post-CCT were calculated. The suppression percentage of PAC and increasing percentage of PRC were also calculated. PA was established according to criteria. Informed written consent was obtained from all participants. This study was registered in chictr.org.cn (identifier, ChiCTR2100047984).

Results: Blood samples of 112 suspected PA patients and 21 healthy volunteers were collected to measure PAC using both CLIA and LC-MS/MS. A positive correlation (r=0.804, P<0.001) was observed between the two assays. CCT were performed in 45 with ARR≥25 and 43 with ARR<25. Data were analyzed in 43 confirmed PA patients and 45 essential hypertension patients. Compare to the PAC, suppression percentage of PAC and increasing percentage of PRC, ARR at 2 h post-CCT presented the largest area under the receiver operating characteristic curve either PAC was measured by LC-MS/MS or by CLIA. The optimal CLIA-specific cut-off of 2 h post-CCT ARR was 26.0, with a sensitivity and specificity of 95.3% and 93.3%, respectively. Moreover, the specificity achieved to 97.8% when combining 2 h post-CCT ARR>26.0 with 2 h post-CCT PAC>15.000 ng/dl.

Conclusion: CLIA presents well correlation with LC-MS/MS in PAC measurement. 2 h post-CCT ARR is the most efficient parameter in PA diagnosis using CCT. The optimal cut-off point for 2 h post-CCT ARR is >26.0 in our study. The diagnosis is more specific when combining 2 h post-CCT ARR>26.0 with 2 h post-CCT PAC>15.000 ng/dl.