Diagnostic value of the fractional excretion of urine potassium for primary aldosteronism

BACKGROUND: Primary aldosteronism (PA) is a common form of secondary hypertension, which usually manifests low blood potassium levels. The fractional excretion of urine potassium (FEK) has been proposed as a useful tool to measure urinary potassium excretion. However, the role of the FEK in PA remains unclear. In the current study, we assessed the diagnostic value of FEK in PA. METHODS: A total of 155 hypertension patients were included in this cross-sectional study, of which 62 were confirmed by a positive screening test for PA. We collected the serum, 24-hr urine samples, and spot urine samples to evaluate the diagnostic value of the spot and 24-hr FEK in the diagnosis of PA and renal potassium loss compared to other indices. The sensitivity and specificity of the related diagnostic indexes were analyzed using receiver operating characteristic (ROC) curves, and the optimal cut-point value of the diagnostic index was determined according to the Youden index (YI) (sensitivity + specificity − 1). Correlation analysis was performed between the spot FEK and 24-hr FEK using Pearson’s correlation coefficient. RESULTS: The spot FEK (7.3 vs. 5.9) and 24-hr FEK (9.3 vs. 8.0) levels were statistical differences between the PA and essential hypertension groups. PA patients had a significant tendency to lose potassium through the kidneys. We found that FEK from spot urine distinguished renal potassium loss with a sensitivity of 86.7% and a specificity of 87.1% at a cut-off of 9.8%. The sensitivity and specificity of the spot FEK in screening PA were 51.6% and 76.3%, respectively. CONCLUSIONS: FEK is significantly related to renal potassium loss. Spot FEK and 24-hr FEK performed a certain diagnostic value for PA, which may be potential indicators for the differential diagnosis of PA.