Introduction: The diagnostic procedure of primary aldosteronism (PA) includes one of four confirmatory tests, of which the saline suppression test (SST) seems to be the most convenient one. Current guidelines recommend SST to be performed in a recumbent position. However, a recent preliminary study demonstrated a higher sensitivity of SST when performed in the upright (i.e. seated) position. Here, we report a case of posture-responsive PA with a negative recumbent SST but clearly positive seated SST.
Case report: A 60-year-old woman was referred to our hospital with the suspicion of PA, based on her 10 years history of rather resistant arterial hypertension with hypokalemia, together with a recent positive aldosterone/renin ratio (ARR) screening test and an adrenal CT scan revealing a unilateral mass of 22×15 mm in her left adrenal gland. On admission, the screening test was repeated; serum aldosterone level was 710 pmol/l and renin concentration was below detection limit. After an overnight rest and potassium level correction, the recumbent SST (2000 ml of saline infusion over 4 hours) was performed. Her aldosterone levels before and after the infusion were 60 and 100 pmol/l, respectively, i.e. the confirmatory test was negative. As our clinical suspicion was still high, we repeated the SST in the upright (sitting) position. In this case the aldosterone levels before and after the infusion were 894 and 657 pmol/l, respectively, while renin concentration stayed suppressed below detection limit, i.e. clearly positive test. The unilateral form of PA was then established by adrenal venous sampling (including cosyntropin stimulation) and the operation is scheduled on the first week in February 2016.
Conclusion: As many patients may have a posture-responsive PA, the seated SST may be preferable over recumbent SST, thus providing better sensitivity.