The aldosterone-to-renin ratio, commonly called the ARR, is a blood test used to screen for primary aldosteronism, a condition in which the adrenal glands produce too much of the hormone aldosterone. It is the standard first-step screening tool for the condition, recommended by endocrine and hypertension guidelines worldwide.1PubMed. Aldosterone-to-renin ratio (ARR) as a screening tool for primary aldosteronism (PA) Primary aldosteronism was once considered rare, but it is now recognized as the cause of roughly one in ten cases of high blood pressure, a dramatic revision from earlier estimates of less than one percent.2Nephrology Dialysis Transplantation. Primary aldosteronism and low-renin hypertension: a continuum? Understanding the ARR, from preparation to interpretation, matters because catching primary aldosteronism opens the door to treatments that can sometimes cure the hypertension outright.
What the Test Is Looking For
Your adrenal glands sit on top of your kidneys and produce aldosterone, a hormone that tells the kidneys to hold on to sodium and release potassium. When your body needs to raise blood pressure or retain fluid, a protein called renin kicks off a chain reaction that ultimately stimulates aldosterone release. In a healthy person, renin and aldosterone work in a feedback loop: more renin leads to more aldosterone, and when aldosterone has done its job, renin production dials back down.
In primary aldosteronism, aldosterone production runs on its own, independent of renin’s signals. The adrenal glands churn out aldosterone whether the body needs it or not. Because the body does not actually need it, renin drops to very low levels. The ARR captures this mismatch: aldosterone stays high while renin falls, pushing the ratio upward. A high ARR flags the possibility that aldosterone is being produced autonomously rather than as part of the normal feedback system.
This is the key distinction from secondary aldosteronism, where both renin and aldosterone are elevated. Secondary aldosteronism shows up in conditions like kidney artery narrowing or severe (“malignant”) hypertension, where the kidneys are genuinely signaling for more aldosterone. In those situations, renin is high, so the ratio stays relatively normal even though aldosterone itself is elevated.3American Heart Journal. Low-renin (“primary”) hyperaldosteronism: Differential diagnosis and distinction of sub-groups within the syndrome
Who Should Be Screened
Historically, doctors ordered the ARR only for patients with resistant hypertension, meaning blood pressure that stays high despite three or more medications. Recent guidelines have broadened that considerably. Screening recommendations now extend to anyone with stage 2 hypertension (readings consistently at or above 140/90) and, in some guidelines, even to all individuals with hypertension.4PubMed Central. Broadening Primary Aldosteronism Screening: Alignment Across Contemporary Guidelines Beyond uncontrolled blood pressure, screening is specifically recommended for people with low potassium, whether spontaneous or triggered by a diuretic.5PubMed. Who needs to be screened for primary aldosteronism?
The push to widen screening stems from the realization that most people with primary aldosteronism have normal potassium levels. The old teaching that low potassium was a hallmark of the disease caused countless cases to be missed. The ARR picks up cases that low potassium alone would not.2Nephrology Dialysis Transplantation. Primary aldosteronism and low-renin hypertension: a continuum? Finding primary aldosteronism early matters because excess aldosterone causes damage to the heart, blood vessels, and kidneys through mechanisms that go beyond simply raising blood pressure.6PubMed. Aldosterone, organ damage and dietary salt
How Renin Is Measured and Why It Matters
One of the confusing aspects of the ARR is that there are two different ways to measure renin, and the choice changes what the numbers look like. The older method, plasma renin activity (PRA), measures how fast renin generates a downstream molecule in the lab. The newer method, direct renin concentration (DRC), uses antibodies to directly count the amount of renin protein in the blood. The two methods correlate well with each other, but they produce numbers in different units and therefore yield different ratio cutoffs.7Endocrine Connections. Diagnostic implications of renin reactivity in confirmatory tests: a comparative study of direct renin concentration and plasma renin activity in primary aldosteronism
When PRA is used in the denominator, the ARR is commonly expressed as ng/dL per ng/mL/h, and a cutoff around 30 is often cited as the screening threshold. When DRC is used, the ratio uses different units and different cutoff numbers. One study found that both methods produced acceptable sensitivity and specificity for identifying primary aldosteronism, and the two ratios correlated strongly with each other.8PubMed. The ratios of aldosterone / plasma renin activity (ARR) versus aldosterone / direct renin concentration (ADRR) The practical issue is that you cannot compare your results to someone else’s, or to a cutoff you found online, unless you know which renin assay was used. Labs across the same country sometimes use different platforms and cutoffs, creating inconsistency in how the test is interpreted.9PubMed. A United Kingdom-wide audit of the laboratory investigation of primary aldosteronism
The DRC method has some practical advantages. It tends to be less affected by certain medications and can be measured from a frozen blood sample, which simplifies shipping to reference laboratories. Some research suggests that beta-blockers raise the ARR significantly within a week when PRA is used but do not change the DRC-based ratio at that same time point, though both methods eventually show a rise with prolonged beta-blocker use.10The Journal of Clinical Endocrinology & Metabolism. Effect of Atenolol on Aldosterone/Renin Ratio Calculated by Both Plasma Renin Activity and Direct Renin Concentration in Healthy Male Volunteers
Medications That Skew the Results
The biggest practical headache with the ARR is that many common blood pressure drugs change aldosterone levels, renin levels, or both, sometimes enough to produce a wrong answer. A critical review of the literature found that many commonly prescribed antihypertensives have significant effects on renin, aldosterone, and the resulting ratio.11PubMed Central. The effect of medication on the aldosterone-to-renin ratio. A critical review of the literature The direction of the interference depends on the drug class.
Beta-blockers are the most notorious offenders for false positives. They suppress renin, which pushes the ratio up even when aldosterone is normal. In one study, about a third of patients taking beta-blockers had a falsely elevated ARR that returned to normal after the drug was stopped.12PubMed. β-Blocker withdrawal is preferable for accurate interpretation of the aldosterone-renin ratio in chronically treated hypertension Clonidine, methyldopa, and nonsteroidal anti-inflammatory drugs can cause the same problem by also suppressing renin.13PubMed. Factors affecting the aldosterone/renin ratio
On the other side, ACE inhibitors and angiotensin receptor blockers (ARBs) can produce false negatives. These drugs raise renin and tend to lower aldosterone, pulling the ratio down and potentially masking primary aldosteronism. In a study of patients with confirmed primary aldosteronism who were given ramipril (an ACE inhibitor), some showed falsely normal ARR results even though their condition had not changed.14PubMed. Effects of Ramipril on the Aldosterone/Renin Ratio and the Aldosterone/Angiotensin II Ratio in Patients With Primary Aldosteronism Among confirmed patients tested on irbesartan (an ARB), roughly one in four gave a false-negative ARR.15PubMed. Drug effects on aldosterone/plasma renin activity ratio in primary aldosteronism
Ideal testing conditions involve stopping medications that heavily interfere, like spironolactone and eplerenone, at least four weeks before the blood draw, and stopping those with moderate interference, like beta-blockers, ACE inhibitors, and ARBs, at least two weeks before. The blood sample itself should be collected midmorning after you have been upright for at least two hours, then seated quietly for five to fifteen minutes.16PubMed Central. Survey of renin and aldosterone testing practices by Ontario laboratories – Providing insight into best practices In practice, stopping all blood pressure medications is not always safe. When that is the case, doctors may use drugs with minimal ARR impact, like slow-release verapamil or hydralazine, to keep blood pressure controlled during the testing period.
Age, Sex, and Other Confounders
Even without medication interference, the ARR is not the same number in everyone. Age is the most consistent independent factor. Renin tends to fall as people get older, which pushes the ratio up. In a study of people with essential hypertension, age was the only independent predictor of the ARR in a model that also accounted for sex and body mass index.17Journal of Hypertension. The effect of age, sex and BMI on the aldosterone-to-renin ratio in essential hypertensive individuals This means an older person could have an elevated ARR simply because of aging physiology, not because they have primary aldosteronism.
Sex differences also appear, especially among younger adults. In one study, women aged 20 to 39 had significantly higher median ARR values than men of the same age, driven by higher aldosterone and lower renin. Women in that age bracket had a median ARR roughly twice that of men.18PubMed. Age- and sex-specific reference ranges are needed for the aldosterone/renin ratio These findings have led to calls for age- and sex-specific reference ranges, though most labs still use a single universal cutoff.
Kidney function is another variable. Chronic kidney disease can alter renin dynamics and shift the ARR, making it harder to distinguish primary aldosteronism from the hormonal changes caused by poor kidney function itself.19PubMed Central. Aldosterone-to-renin ratio acts as the predictor distinguishing the primary aldosteronism from chronic kidney disease Salt intake matters too. The standard preparation protocol calls for unrestricted dietary salt before the test, because a very low-salt diet stimulates renin and can obscure the pattern.
What Happens After a Positive Screen
A high ARR is a screening result, not a diagnosis. Because the test has imperfect specificity, especially in older patients and those on incompletely washed-out medications, guidelines have traditionally called for a confirmatory test before proceeding. These tests work by trying to suppress aldosterone and seeing if it stays stubbornly high. The most common options include the saline infusion test (where you receive intravenous salt water over several hours) and the captopril challenge test (where you take a single dose of an ACE inhibitor and see if aldosterone drops).
The evidence behind these confirmatory tests is weaker than many clinicians realize. A systematic review and meta-analysis that pooled data from 55 studies found large variations in how the tests were conducted and interpreted, high risk of bias in more than half of studies, and concluded that under most conditions, confirmatory testing led to an excess of missed cases rather than a tighter diagnosis.20PubMed Central. Performance of Confirmatory Tests for Diagnosing Primary Aldosteronism: a Systematic Review and Meta-Analysis Some newer guidelines have begun questioning whether confirmatory testing is always necessary, particularly when the initial ARR is very high and other biochemical features are strongly suggestive.
Figuring Out Which Adrenal Gland Is the Problem
Once primary aldosteronism is confirmed, the next question is whether the excess aldosterone comes from one adrenal gland or both, because the answer determines treatment. A single overproducing gland, usually harboring a small benign tumor called an adenoma, can be cured with surgery. When both glands are overactive, a pattern called bilateral adrenal hyperplasia, surgery is not helpful and treatment relies on medications that block aldosterone’s effects.
CT scans catch many adenomas, but they miss small ones and can mislead by flagging harmless lumps that are not producing aldosterone. The recommended procedure for identifying which side is the culprit is adrenal vein sampling (AVS), where a catheter is threaded into the veins draining each adrenal gland and blood samples are taken to compare aldosterone output side by side.21PubMed Central. Adrenal Vein Sampling for Primary Aldosteronism: Recommendations From the Australian and New Zealand Working Group A lateralization index greater than four during hormone-stimulated sampling is the most widely accepted threshold for calling one side dominant.22Endocrinology and Metabolism. Adrenal Venous Sampling for Subtype Diagnosis of Primary Hyperaldosteronism
Despite being considered the gold standard, AVS remains markedly underused. It is technically demanding, available at relatively few centers, and uncomfortable for patients. An expert consensus noted that the procedure’s low uptake is a major barrier to identifying people who could benefit from curative surgery.23PubMed. An expert consensus statement on use of adrenal vein sampling for the subtyping of primary aldosteronism Research into imaging-based and biochemical alternatives is ongoing, but none has yet replaced AVS in practice.
How the Two Main Subtypes Differ
People with an adenoma and people with bilateral hyperplasia look similar on paper: both have hypertension, both may have low potassium, and their lab values overlap substantially. One study found that although patients with an adenoma tended to have lower potassium and higher aldosterone on average, the overlap between groups was too large to reliably distinguish them in any individual case using blood tests alone.24PubMed. Primary aldosteronism: difference in clinical presentation and long-term follow-up between adenoma and bilateral hyperplasia of the adrenal glands
There are subtle physiological differences, however. In patients with an adenoma, aldosterone production tends to track closely with cortisol, following the body’s natural circadian rhythm: highest in the early morning, declining through the day. Standing up does not raise aldosterone much, because the adenoma operates somewhat independently of the normal renin-mediated signal. In bilateral hyperplasia, aldosterone responds more to posture and renin-related stimuli, often rising when the patient stands or walks.25PubMed. Aldosterone regulation in primary aldosteronism: differences between adenoma and bilateral hyperplasia This distinction is occasionally used as a supplementary diagnostic clue, though it is not reliable enough to replace AVS.
Treatment and Why It Depends on the Subtype
For unilateral disease, the standard treatment is surgical removal of the affected adrenal gland, typically done laparoscopically. Surgery often dramatically improves or cures the hypertension and normalizes potassium. A meta-analysis comparing surgery with targeted medical therapy confirmed that accurate subtyping is essential because surgery is only appropriate for unilateral disease.26PubMed Central. Time to Benefit of Surgery vs Targeted Medical Therapy for Patients With Primary Aldosteronism: A Meta-analysis
For bilateral disease, treatment centers on mineralocorticoid receptor antagonists, most commonly spironolactone or eplerenone, which block aldosterone’s effects at the tissue level. These drugs lower blood pressure and protect organs but do not eliminate the excess aldosterone itself. A comparison of surgical and medical treatment in patients with unilateral adenoma found that both approaches reduced fluid overload and potassium normalized with both, though surgery achieved faster improvements in some inflammatory and fluid markers at the four-week mark, with the differences largely evening out by twelve weeks.27Scientific Reports. Effect of Treatment on Body Fluid in Patients with Unilateral Aldosterone Producing Adenoma: Adrenalectomy versus Spironolactone
Organ Damage Beyond Blood Pressure
One of the reasons catching primary aldosteronism matters so much is that excess aldosterone does not just raise blood pressure. Long-term exposure to high aldosterone or activation of the receptors it binds causes direct injury to the heart, blood vessels, and kidneys through mechanisms that operate independently of blood pressure.6PubMed. Aldosterone, organ damage and dietary salt People with primary aldosteronism have higher rates of atrial fibrillation, heart attack, and stroke than people with the same blood pressure levels from ordinary hypertension.2Nephrology Dialysis Transplantation. Primary aldosteronism and low-renin hypertension: a continuum? This extra cardiovascular risk is the reason endocrine specialists are so insistent about not dismissing a positive ARR screen. Treating the aldosterone excess, not just the blood pressure number, appears to reduce that added risk.
Familial Forms of Primary Aldosteronism
Most primary aldosteronism is sporadic, but there are inherited forms collectively called familial hyperaldosteronism. These are rare, but they matter because they can affect children and young adults, and genetic testing can identify family members who carry the mutation before they develop severe hypertension. The ARR is recommended as the initial screening test in these families as well. In one study, all affected children from families with a particular inherited form of the disease had elevated ARRs, but only one out of eight had low potassium, reinforcing that potassium alone is unreliable as a screening marker.28European Journal of Endocrinology. Familial hyperaldosteronism: an European Reference Network on Rare Endocrine Conditions clinical practice guideline The most well-known familial type, sometimes called glucocorticoid-remediable aldosteronism, responds to low-dose steroid treatment rather than surgery. Identifying these families changes management for multiple generations.
Why Lab Standardization Remains an Unsolved Problem
Even after you prepare properly, get the blood drawn under ideal conditions, and your doctor uses the right cutoff for the renin assay method on your particular sample, there is a structural problem: labs do not agree on what “normal” looks like. A UK-wide audit of laboratories investigating primary aldosteronism found considerable variation in reference intervals and cutoffs across centers, and these differences were not fully explained by the use of different analytical platforms.9PubMed. A United Kingdom-wide audit of the laboratory investigation of primary aldosteronism This means a sample sent to one lab might flag as positive and the same sample sent to another might not. International efforts to harmonize aldosterone and renin assays are underway but have not yet reached the clinic in a meaningful way. If your ARR comes back borderline, it is worth asking which assay method the lab used and whether the cutoff your doctor is applying was validated for that specific platform.