Assay for
Aldosterone:
Enzymatic Radioimmunoassay (RIA).
Precautions:
Do not perform this test in patients with severe uncontrolled hypertension, renal insufficiency, cardiac insufficiency, cardiac arrhythmia, or severe hypokalemia [1].
Interpretation:
With concomitant urinary sodium excretion > 200 mEq/24 h and creatinine > 15 mg/kg/24 h for men and 10 mg/kg/24 h for women respectively; PA is unlikely if urinary aldosterone is <10 mcg/24 hr. Elevated urinary aldosterone excretion > 12 mcg/24 h makes PA highly likely [1].
Caveats:
This test is the most cost-effective test, but the conditions are not strictly controlled and patient compliance on urine collection is a potential limitation [2].
Stop all potassium sparing and potassium wasting diuretics for 4 weeks. Stop beta-adrenergic blockers, central alpha-2 agonists (e.g., clonidine, alpha-methyldopa), non-steroidal anti-inflammatory drugs, angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, renin inhibitors, dihydropyridine calcium channel antagonists for 2 weeks [1]. Blood pressure can be controlled with one or more of the following agents: verapamil extended release, selective alpha-1 blocker (e.g. Doxazosin), and hydralazine [1].
In the presence of renal disease urinary aldosterone levels may be falsely low [1].
When aldosterone levels are indeterminate (urinary aldosterone excretion 10–12 mcg/24 h) other confirmatory tests should be performed such as the IV saline loading test or the Captopril challenge test [1]. Although the Fludrocortisone suppression test may have a better diagnostic accuracy, it requires hospitalization and is generally not performed in North America.Related posts:
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