Aldosterone to Renin Ratio (ARR) Calculator
Results:
Calculated ARR:
Note: Interpretation depends on local laboratory cutoffs and standardized testing conditions.
Understanding the Aldosterone to Renin Ratio (ARR)
The Aldosterone to Renin Ratio (ARR) is the most reliable screening tool used by clinicians to identify patients with Primary Aldosteronism (PA), also known as Conn's Syndrome. This condition occurs when the adrenal glands produce too much aldosterone, leading to hypertension (high blood pressure) and sometimes low potassium levels (hypokalemia).
How the Calculation Works
The calculator uses the concentration of aldosterone in the blood and divides it by the renin level. However, because medical laboratories use different units and testing methods, conversions are often necessary for a standardized interpretation:
- Aldosterone: Commonly measured in ng/dL (nanograms per deciliter) or pmol/L (picomoles per liter).
- Renin: Measured as either Plasma Renin Activity (PRA, in ng/mL/h) or Plasma Renin Concentration (PRC, in mU/L).
The standard formula for the ratio used in most clinical guidelines is Aldosterone (ng/dL) / PRA (ng/mL/h).
Interpreting Your ARR Results
While lab-specific reference ranges vary, the following cutoffs are generally accepted for screening purposes:
| ARR Value (ng/dL per ng/mL/h) | Clinical Significance |
|---|---|
| Below 20 | Negative screening result. Primary Aldosteronism is unlikely. |
| 20 – 30 | Borderline. Requires clinical correlation with potassium and aldosterone levels. |
| Above 30 | Positive screening result. Suggestive of Primary Aldosteronism. |
Factors That Affect ARR Accuracy
The ARR is highly sensitive to external factors. To get an accurate reading, patients must often follow specific protocols before the blood draw:
- Medications: Beta-blockers, ACE inhibitors, and diuretics can significantly alter renin and aldosterone levels. Some doctors require stopping these medications for 2–4 weeks before testing.
- Potassium Levels: Low potassium (hypokalemia) can suppress aldosterone secretion, potentially leading to a false-negative result.
- Sodium Intake: High salt intake can suppress the renin-angiotensin system, affecting the ratio.
- Posture: Blood should ideally be drawn after the patient has been upright (sitting or standing) for at least two hours and then sitting for 5–15 minutes.
Example Calculation
If a patient has an Aldosterone level of 15 ng/dL and a Plasma Renin Activity (PRA) of 0.3 ng/mL/h, the calculation is:
15 / 0.3 = 50
In this case, an ARR of 50 is well above the threshold of 30, indicating a strong possibility of primary aldosteronism, warranting further diagnostic procedures like a CT scan of the adrenal glands or a salt loading test.