Function tests

Confirmation test of pathological aldosterone-renin-quotient (ARQ) on suspicion of primary hyperaldosteronism (Conn-syndrome).

The ACE-inhibitor Captopril inhibits angiotensin and therefore aldosterone-production. Captopril inhibits the angiotensin-converting enzyme and aldosterone-production, which is influenced by the angiotensin. The test is based on the differing reactions of plasma-renin-activity and plasma-aldosterone 1 hours or 2 hours after intake of 25 – 50 mg captopril (ACE-inhibitor) in healthy persons and patients with primary hyperaldosteronism.

Aldosterone, renin

2 ml serum and 2 ml EDTA-plasma before (0 min), and 60 and 120 min after administration of 25 – 50 mg captopril. Freeze samples, if they are sent by mail.

• Blood collection for aldosterone and renin prior to oral administration of 25 – 50 mg captopril in tablet form (0 min value)
• Blood collection for aldosterone and renin 1 hour and 2 hours after captopril administration.

There is normal aldosterone-suppression, if aldosterone-concentration decreases by more than 30 % of the initial value.  Renin-concentration does not increase, but usually remains suppressed. Unfortunately, false-negative results often occur, due to the very different resorption rates and thus bioavailability of captopril.

As an alternative, the saline test in sitting position, which has markedly higher sensitivity, can be used (please refer to sections “Aldosterone suppression test” and “Sodium stress test”)