Primary aldosteronism (PA), the most common endocrine cause of hypertension, is screened using the plasma aldosterone to renin ratio (ARR) followed by one of several confirmatory tests. The saline suppression test (SST) is the most widely used but it is contraindicated in patients with renal insufficiency or congestive heart failure. The captopril challenge test (CCT) is a safe, inexpensive and convenient alternative, but the diagnostic thresholds and reported accuracy vary between centres. No comparative studies have been conducted in low-middle-income countries where CCT is likely more affordable than the SST. This study aims to determine prospectively the diagnostic accuracy of the CCT compared to the SST in a Bangladeshi population.
Consecutive hypertensive patients with an ARR > 50 pmol/mIU underwent both the SST and CCT. Using the SST as the reference standard, with a plasma aldosterone concentration (PAC) post SST ≥ 170 pmol/l considered diagnostic of PA, the diagnostic accuracy of the CCT, based on three published diagnostic parameters at either 1- or 2-hours post-captopril, was calculated.
Overall, 114 patients completed both confirmatory tests (median age 43.3±11.9 year, 71% female). The diagnostic accuracy of the post-captopril PAC was significantly higher than the post-captopril ARR or the percentage PAC suppression at either 1- or 2-hours. PAC > 333 pmol/L at 1- or 2-hour post-captopril had a sensitivity of 52.6% or 41.1% and specificity of 92.9% or 94.7% respectively. The diagnostic accuracy of the post-captopril PAC was similar between patients with high and low sodium intake. Post-captopril PAC < 151 pmol/L or > 347 pmol/L at 1 hour can rule-out or rule-in the diagnosis of PA respectively.
Our results indicate that based on post-captopril PAC, the CCT had comparable diagnostic accuracy to the SST and can be considered a convenient and reliable confirmatory test for PA.