Renin Test: Why the Number Means Nothing Without Aldosterone

Mixing these up is the most common way a renin result is misread.

PRA measures how quickly the sample produces angiotensin I, so it is a rate. Direct renin, sometimes printed as active renin, measures the amount of renin protein. The suppression levels above are the ones the Endocrine Society uses, and they show the trap: a renin of 5 is unremarkable on a PRA report and clearly suppressed on a DRC report. The guide to lab units covers conversions like this.

When the adrenal glands make aldosterone independently, renin falls toward zero and the aldosterone-to-renin ratio (ARR) rises. A single cutoff of 30 is widely quoted, but the Endocrine Society uses different thresholds depending on how renin and aldosterone were measured:

Aldosterone also has to reach a minimum: at least 10 ng/dL (277 pmol/L) by immunoassay or 7.5 ng/dL (208 pmol/L) by mass spectrometry, because a large ratio built on a very small aldosterone means something different. For example, a PRA of 0.4 ng/mL/h with an aldosterone of 15 ng/dL gives a ratio of 37.5, above 20, with aldosterone above its minimum: a positive screen. Local lab cutoffs take priority where a lab publishes them.

Usually not. The 2025 ACC/AHA high blood pressure guideline recommends continuing blood pressure medicines for the first screen, to avoid delay, with one exception: mineralocorticoid receptor antagonists such as spironolactone and eplerenone, which are typically paused for four weeks. Stopping blood pressure treatment can be dangerous, so any change is the prescriber's decision. If the screen is negative or borderline but suspicion stays high, the same guideline allows a repeat with interfering medicines temporarily stopped.

Other details matter more than people expect. Renin and aldosterone are highest in the morning and change with posture, so the screen is drawn in the morning with the person seated. Salt restriction and diuretics raise renin and a high-salt diet lowers it, so the test is done on your usual diet. MedlinePlus advises avoiding natural black licorice for at least two weeks beforehand; most US licorice candy contains none, so the ingredient label is what counts. Birth control pills and stress can also shift the result.

A suppressed renin in someone with high blood pressure is what sends doctors to the aldosterone result. The test is often ordered for blood pressure that responds poorly to standard medicines, or with signs of low potassium such as muscle cramps, weakness, thirst, tiredness or palpitations; the 2025 guideline asks for potassium to be measured with renin and aldosterone. Renin can also be low with a high-salt diet, salt-sensitive high blood pressure, diabetic kidney disease, and steroid medicines that cause salt retention.

A normal or high renin argues against primary aldosteronism and points elsewhere.

When renin and aldosterone are both high, the aldosterone is responding to a real signal (secondary aldosteronism). High renin with low aldosterone points toward adrenal insufficiency, where cortisol is the next result to check.

A clearly negative screen usually ends the question. A positive or borderline one leads to confirmatory testing and then to working out whether one adrenal gland or both are responsible, which changes the treatment; the aldosterone page covers those tests. For primary aldosteronism, the Endocrine Society recommends mineralocorticoid receptor antagonists as the first-line medical treatment, the same drugs that have to be paused before a repeat screen. The guide to reading a hormone panel shows how renin and aldosterone sit together on a hormone panel.