Background:
Primary hyperaldosteronism (PHA) accounts for 5-10% of patients with hypertension (1). Saline suppression test (SST) is a commonly used confirmatory test in the diagnosis of PHA. Although potassium (K) is checked at baseline with recommendations to adequately replace prior to SST, there are no recommendations to routinely check potassium post-SST. This contrasts guidelines for the fludrocortisone suppression test (FST) which is known to cause hypokalaemia. A previous study monitored K levels post-SST in a subgroup of patients, and found a non-significant decrease (-0.05 +/-0.2mmol/L) in potassium levels post-SST (2). We report a retrospective series of patients who became hypokalaemic in the 2 hour period post-SST.
Methods:
A retrospective audit was conducted of patients with confirmed PHA who underwent SST between 2005 and 2015. Pre- and 2 hour post-test potassium, aldosterone and renin levels were measured. Results are expressed as mean ± standard error of the mean (SEM) and number (%).
Results:
Twenty five patients were included in the final analysis; 13 (52%) were males, and mean age 53 ± 10.5 years. Overall, there was no difference in the mean pre- and post-SST potassium levels (p=0.08). However, there was an inverse correlation between pre-SST K and the change in post-test K levels (p=0.01); with the highest pre-test K patients experiencing the greatest decline in post-K levels. Eight (32%) were hypokalaemic (K<3.5mmol/L) pre-SST and required intravenous or oral K supplements.
For patients that were normokalaemic pre-SST, there was a significant decrease in serum potassium levels post-SST (3.7±0.05 vs. 3.5±0.08, p=0.01). Seven subjects (41%) who were normokalaemic pre-test became hypokalaemic post-SST; and 5 (29%) remained hypokalaemic on day 2.
Conclusion:
Hypokalaemia is common post-saline suppression test in primary hyperaldosteronism. The pathophysiology remains unclear. We recommend that potassium levels be routinely measured post-test and on day 2 to detect persistent hypokalaemia.