Context: in patients with primary aldosteronism (PA) it is fundamental to distinguish between subtypes that benefit from different therapies. CT scans lack sensitivity and specificity and must be followed by adrenal venous sampling (AVS). Since AVS is not widely available, a list of clinical criteria has been suggested that indicates the presence of an aldosterone-producing adenoma (APA).

Objective and design: to test the sensitivity and specificity of the last generation CT scans; -to test prospectively the usefulness of clinical criteria in the diagnosis of APA; -to develop a flow-chart to be used when AVS is not easily available.

Setting: hypertensives referred to our Hypertension Unit.

Patients: 71 patients with confirmed PA.

Intervention: all patients underwent CT scan and AVS.

Main outcome measure: final diagnosis of APA.

Results: 44% and 56% of patients were diagnosed as having an APA and a bilateral adrenal hyperplasia (BAH), respectively. 20% of patients with PA displayed hypokalemia. CT scans displayed a sensitivity of 0.87 and a specificity of 0.71. The posture test displayed a lower sensitivity and specificity (0.64 and 0.70, respectively). The distribution grades of hypertension were not significantly different between APA and BAH. Biochemical criteria of "high probability" of APA displayed a sensitivity of 0.32 and a specificity of 0.95.

Conclusions: this study underlines the central role of AVS in the subtype diagnosis of PA. The use of the clinical criteria to distinguish between APA and BAH did not display a satisfactory diagnostic power.