Objective   To explore the electrolyte characteristics between different types of primary aldosteronism (PA), especially the value of serum potassium and the ratio of sodium to potassium after saline infusion test (SIT) in differential diagnosis of PA.

  Methods  The clinical data was collected from 135 patients who received screening for the causes of hypertension from Jan. 2009 to Dec. 2018 in West China Hospital. The patients were divided into two groups: essential hypertension group (EH group, 34 patients) and primary aldosteronism group (PA group, 101 patients). PA patients were divided into aldosterone-producing adenoma group (APA group, 60 patients) and idiopathic hyperaldosteronism group (IHA group, 41 patients). To analyze the value of serum potassium and the ratio of sodium to potassium after SIT in the differential diagnosis of PA with receiver operating characteristic (ROC) curve.

  Results  Compared with EH group, the serum potassium level of APA group was lower either before or after SIT (P<0.01). The ratio of sodium to potassium before and after SIT in APA group were higher than that in EH group (P<0.05). There were no differences between APA group and IHA group in the level of serum potassium and the ratio of sodium to potassium before SIT. The level of serum potassium after SIT in APA group was lower than that in IHA group (P<0.01), and the ratio of sodium to potassium was higher (P<0.05). The area under ROC curve (AUC) of serum potassium level and the ratio of sodium to potassium after SIT were 0.641 and 0.646, respectively, while the AUC of aldosterone level was 0.788. The optimal cut-off value of serum sodium level was 3.56 mmol/L, with a sensitivity and specificity of 46.7% and 85.4%. The optimal cut-off value of ratio of sodium to potassium was 39.09, with 53.3% and 80.5% in sensitivity and specificity.

  Conclusion  The serum potassium and the ratio of sodium to potassium after SIT has limited diagnostic value for its low sensitivity in differential diagnosis of PA.