Using plasma aldosterone concentrations at 1 h of saline infusion test for the diagnosis of primary aldosteronism

Objective: Saline infusion test (SIT) requires 2 l of isotonic saline for intravenous infusion over 4 h to suppress plasma aldosterone concentration (PAC). To shorten the procedure time and minimize the volume load, we study the performance of SIT at 1, 2 and 4 h for diagnosing primary aldosteronism. Methods: This is a cross-sectional study. PAC was measured before and 1, 2 and 4 h after saline infusion at a rate of 500 ml/h in patients suspected to have primary aldosteronism. Primary aldosteronism was diagnosed based on 4 h PAC, adrenal imaging and/or adrenal venous sampling (AVS). Results: Of the 93 patients, 32 had primary aldosteronism. The area under the receiver operating characteristic (ROC) curve of the 1, 2 and 4 h PAC were not statistically different. All of the nonprimary aldosteronism group had a 1 h PAC lower than 15 ng/dl and all of the primary aldosteronism group had a 1 h PAC higher than 5 ng/dl. Nearly 30% of the nonprimary aldosteronism and primary aldosteronism groups had a 1 h PAC between 5 and 15 ng/dl (equivocal range) and could be discriminated by using percentage suppression of 1 h PAC from baseline. Using 1 h PAC of more than 15 ng/dl together with percentage suppression of 1 h PAC from baseline of less than 60 when 1 h PAC was 5–15 ng/dl, primary aldosteronism could be detected with a sensitivity of 93.7% and specificity of 96.7%. Conclusion: The 1 h SIT has a similar diagnostic performance to the standard SIT. Using 1 h PAC together with percentage suppression from baseline when 1 h PAC is equivocal, primary aldosteronism can be diagnosed with good accuracy.