Background: The plasma aldosterone concentration (PAC), renin and aldosterone-renin ratio (ARR) are used to screen for primary aldosteronism (PA). A recent study (Yozamp et al. Hypertension. 77: 891, 2021) reported substantial intraindividual variability of PAC and ARR (based on plasma renin activity) in the context of usual antihypertensive therapy. The intraindividual variability of PAC and direct renin concentration (DRC), a more widely used measurement of renin, in the absence of interfering medications is unknown but important for the interpretation of a single ARR performed to screen for PA.
Method: In this retrospective study of patients who attended an Endocrine Hypertension Service from May 2017 to July 2021, those with at least two ARR results off interfering medications were analysed. PA was formally diagnosed using the seated saline suppression test following an abnormal ARR > 70 pmol/L:mU/L. Variability in PAC and DRC was calculated as coefficient of variation (CV = standard deviation / mean) and percent difference (difference between highest and lowest values / mean).
Results: The final analysis included 223 patients (55% females), with a median age of 52 years. Significant variability was seen in both PAC and DRC with CV of 24% and 41%, and percent difference of 45% and 75%, respectively. No significant differences in CV or percent difference were seen between patients with or without PA, and in patients with different subtypes of PA. Forty-five out of the 180 patients with PA (25%) could have had a missed diagnosis if the ARR had not been repeated.
Conclusion: Intraindividual variability in PAC, DRC and hence ARR occurs in a significant number of patients being investigated for PA. Findings from our study advocate for the measurement of at least two ARR, particularly if the first ARR is normal, before discounting the potential diagnosis of PA.