Decrease in serum potassium levels post saline suppression test in primary aldosteronism: an under-recognised phenomenon?

Seventeen subjects with confirmed primary aldosteronism and stable serum potassium (K) levels ≥ 3.5 mmol l-1 underwent saline suppression testing. They were retrospectively evaluated for changes in serum K levels post test. We found that there was a significant decrease in serum K levels post saline suppression test (3.7 ± 0.05 vs 3.5 ± 0.08, P = 0.01). This effect of saline suppression testing on serum K levels is not well described. We conclude that a decrease in serum K is common post-saline suppression test, even in subjects who are normokalemic pretest. The factors which predispose to the decrease in serum K level post saline load remain unclear.