What are the diagnostic tests for primary aldosteronism (Hyperaldosteronism)?

From the Guidelines

Testing for primary aldosteronism should involve a two-step process: initial screening with the aldosterone-to-renin ratio (ARR) and subsequent confirmatory testing if the ARR is elevated, as recommended by the 2017 ACC/AHA/AAPA/ABC/ACPM/AGS/APhA/ASH/ASPC/NMA/PCNA guideline 1. The initial screening should be done with a blood test measuring the ARR, which should be performed in the morning after the patient has been up for at least 2 hours and seated for 5-15 minutes before blood collection.

• Certain medications can affect results, so ideally, patients should stop interfering medications like beta-blockers, ACE inhibitors, ARBs, and diuretics for 2-4 weeks before testing, with appropriate medical supervision.
• Potassium levels should be normalized before testing.
• The most commonly used cutoff value for the ARR is 30 when plasma aldosterone concentration is reported in nanograms per deciliter (ng/dL) and plasma renin activity in nanograms per milliliter per hour (ng/mL/h) 1.
• Because the aldosterone:renin activity ratio can be influenced by the presence of very low renin levels, the plasma aldosterone concentration should be at least 10 ng/dL to interpret the test as positive 1. If the ARR is elevated, confirmatory testing is needed, which may include the oral sodium loading test, saline infusion test, captopril challenge test, or fludrocortisone suppression test 1.
• These tests assess whether aldosterone production remains inappropriately high despite maneuvers that should suppress it. Once primary aldosteronism is confirmed, additional testing such as adrenal CT or MRI scans and adrenal vein sampling may be performed to determine if the condition is caused by an adrenal adenoma or bilateral adrenal hyperplasia, which guides treatment decisions 1. This testing process is important because primary aldosteronism is a common but underdiagnosed cause of resistant hypertension, and proper diagnosis allows for targeted treatment, including unilateral laparoscopic adrenalectomy or medical therapy with spironolactone or eplerenone 1.

From the Research

Testing for Primary Aldosteronism

To test for primary aldosteronism, the following steps can be taken:

• The plasma aldosterone-to-renin ratio (ARR) is currently recommended as a screening test for primary aldosteronism 2, 3, 4, 5.
• Patient preparation is crucial, including adjusting existing antihypertensive medications to avoid diagnostic errors 3.
• If the ARR is abnormally elevated, patients should be referred to a specialist for confirmatory testing 3.
• Confirmatory tests include:
  • Saline infusion test (SIT) 6
  • Captopril challenge test (CCT) 6
  • Fludrocortisone suppression test (FST) 2, 6
  • Oral sodium loading test (SLT) 6
• Adrenal venous sampling (AVS) is the only dependable way to differentiate unilateral from bilateral forms of primary aldosteronism 2, 4, 5.
• Genetic testing for the causative 'hybrid' 11beta-hydroxylase/aldosterone synthase gene can facilitate detection of the glucocorticoid-remediable form of primary aldosteronism (familial hyperaldosteronism type I) 2.

Diagnostic Accuracy of Confirmatory Tests

The diagnostic accuracy of confirmatory tests has been evaluated in several studies:

• A systematic review and meta-analysis found that CCT and SIT exhibit high and comparable accuracy for diagnosing primary aldosteronism, with no significant differences between the two tests 6.
• The pooled sensitivity and specificity of CCT were 0.87 and 0.84, respectively, while those of SIT were 0.85 and 0.87, respectively 6.
• FST also showed high sensitivity and specificity, although the number of studies evaluating this test was limited 6.