From the Guidelines
For the workup of hyperaldosteronism, plasma (not serum) samples should be used for both renin and aldosterone measurements. The preferred test is a plasma aldosterone concentration to plasma renin activity ratio (ARR) 1. Blood should be collected in the morning after the patient has been upright for at least 2 hours and seated for 5-15 minutes before the draw. Certain medications can affect results, so ideally, medications like beta-blockers, ACE inhibitors, ARBs, and diuretics should be discontinued for 2-4 weeks before testing, if safe to do so. Potassium levels should be normalized before testing as hypokalemia can suppress aldosterone production and lead to false-negative results. The use of plasma rather than serum is important because the clotting process in serum collection tubes can activate the renin-angiotensin system and potentially alter results. Additionally, samples should be processed promptly and according to the laboratory's specific requirements, as renin activity can be affected by temperature and handling conditions.
Some key points to consider when interpreting the results include:
- The plasma aldosterone:renin activity ratio can be influenced by the presence of very low renin levels, and the plasma aldosterone concentration should be at least 10 ng/dL to interpret the test as positive 1.
- Patients should have unrestricted salt intake, serum potassium in the normal range, and mineralocorticoid receptor antagonists (e.g., spironolactone or eplerenone) withdrawn for at least 4 weeks before testing 1.
- The diagnosis of primary aldosteronism generally requires a confirmatory test (intravenous saline suppression test or oral salt-loading test) 1.
- If the diagnosis of primary aldosteronism is confirmed, referral to a hypertension specialist or endocrinologist is recommended for further evaluation and treatment 1.
It's worth noting that the evidence from 1 is older and not as highly ranked as the other studies, so it is not considered in the recommendation. The most recent and highest quality studies 1 all support the use of plasma samples for renin and aldosterone measurements.
From the Research
Diagnosis of Hyperaldosteronism
- The diagnosis of primary aldosteronism involves measuring plasma aldosterone concentration and plasma renin activity, with an elevated aldosterone-renin ratio indicating independent aldosterone secretion 2, 3, 4.
- The aldosterone-to-renin ratio is the most sensitive screening test for primary aldosteronism 4.
- Confirmatory tests include the captopril challenge, oral or intravenous salt loading, or fludrocortisone suppression 2, as well as the furosemide test 4 and the dexamethasone enhanced seated saline suppression test 5.
Sample Collection
- The studies do not specifically mention whether serum or plasma samples should be used for renin and aldosterone measurements.
- However, the texts consistently refer to "plasma aldosterone concentration" and "plasma renin activity", suggesting that plasma samples may be preferred 2, 3, 4, 6, 5.
Testing Procedures
- Initial case detection is performed by simultaneously measuring plasma aldosterone concentration and plasma renin activity 2.
- After a positive case detection, confirmatory testing should be performed to confirm the diagnosis of primary aldosteronism 2, 4, 5.
- Adrenal computed tomography and adrenal vein sampling should be performed to differentiate unilateral from bilateral adrenal production of aldosterone 2, 3, 4, 6, 5.