Which Patients with Positive ARR Should Undergo Confirmatory Testing
Not all patients with a positive aldosterone-renin ratio require confirmatory testing—patients with markedly elevated aldosterone (≥20 ng/dL or ≥550 pmol/L) on at least two measurements with suppressed renin can proceed directly to subtype evaluation, while those with very low aldosterone (<9 ng/dL or <240 pmol/L) can have PA ruled out without further testing. 1
Patients Who DO NOT Need Confirmatory Testing
PA Can Be Confirmed Without Testing When:
- Aldosterone >20 ng/dL (>550 pmol/L) on at least two separate measurements AND
- Suppressed renin (PRA ≤1 ng/mL/h or DRC ≤8.2 mU/L) AND
- Elevated ARR (>20 for PRA or >70 for DRC when using immunoassay)
The risk of false positives in this scenario is very slight (approximately 2-8%), making confirmatory testing unnecessary 1. These patients can proceed directly to adrenal imaging and subtype evaluation.
PA Can Be Ruled Out Without Testing When:
- Aldosterone <9 ng/dL (<240 pmol/L) on two assessments AND
- Normal or elevated renin
The risk of false negatives is minimal in this group, and PA can be confidently excluded 1.
Patients Who REQUIRE Confirmatory Testing
All patients with positive ARR who fall between these extremes must undergo confirmatory testing 1. This includes:
- Patients with aldosterone between 9-20 ng/dL (240-550 pmol/L) with elevated ARR
- Patients with elevated ARR but ambiguous aldosterone levels
- Any patient where the screening result is not definitively in one of the above categories
Rationale for Confirmatory Testing in This Group:
The literature demonstrates that 30-50% of hypertensive patients with positive ARR screening have aldosterone levels that can be suppressed on confirmatory testing, representing false positives 1. Additionally, aldosterone shows pulsatile secretion making ARR intrinsically variable—in one Japanese series of 71 surgically confirmed Conn adenomas, plasma aldosterone and ARR were normal on at least one reading in 39% and 31% of patients respectively 1.
Important Caveats
Exception for Highly Suggestive Cases:
According to the most recent 2025 Endocrine Society guideline 2, confirmatory testing may be bypassed in patients with spontaneous hypokalemia combined with the markedly elevated aldosterone criteria above, though this is not explicitly stated as strongly as in prior guidelines.
Medication Management:
Before both screening and confirmatory testing, manage interfering medications based on individual safety and feasibility. If screening is negative but the patient has hypokalemia, correct potassium to within normal range and repeat screening 2.
Choice of Confirmatory Test:
When confirmatory testing is indicated, the 2016 SFE/SFHTA/AFCE consensus recommends saline infusion test as first-line, or captopril challenge test if sodium loading is contraindicated (e.g., severe heart failure or uncontrolled hypertension) 1. The 24-hour urine aldosterone collection mentioned in your question can serve as an alternative confirmatory test, with recent data suggesting a cut-off >8.7 μg/24h provides 89% sensitivity and 91% specificity 3.
Clinical Pitfall:
Do not skip confirmatory testing in the intermediate aldosterone range (9-20 ng/dL) simply because ARR is elevated—this leads to unnecessary invasive procedures like adrenal vein sampling in patients who do not actually have PA 1.