Is plasma renin activity higher in a patient with a 1.5 cm non-functioning adrenal adenoma and hypertension?

Plasma Renin Activity in Non-Functioning Adrenal Adenoma with Hypertension

In a patient with a 1.5 cm non-functioning adrenal adenoma and hypertension, plasma renin activity would typically be normal or elevated (not suppressed), as the adenoma is by definition non-functioning and therefore not producing excess aldosterone or other hormones that would suppress renin.

Understanding the Biochemical Profile

The key distinction here is that a non-functioning adenoma does not autonomously secrete hormones. Therefore:

• Plasma renin activity (PRA) should be normal or elevated in response to the hypertension itself, particularly if the patient is on certain antihypertensive medications like ACE inhibitors or diuretics 1
• Plasma aldosterone would be normal since the adenoma is not producing aldosterone 1
• The aldosterone-to-renin ratio (ARR) would be normal (typically <20-30), effectively ruling out primary aldosteronism 1, 2

Why This Matters Clinically

Screening Requirements for Adrenal Incidentalomas

All patients with adrenal incidentalomas should undergo functional evaluation, including 1:

• Plasma aldosterone and renin activity to screen for primary aldosteronism
• 1 mg dexamethasone suppression test to screen for autonomous cortisol secretion (recommended for all adrenal incidentalomas) 1
• Plasma free metanephrines if the mass has attenuation ≥10 HU on non-contrast CT 1

What "Non-Functioning" Actually Means

A truly non-functioning adenoma means 1:

• Normal cortisol suppression on 1 mg dexamethasone suppression test (serum cortisol <50 nmol/L or <1.8 μg/dL at 8 AM) 1
• Normal aldosterone-to-renin ratio (<20-30) with normal plasma aldosterone 1, 2
• Normal plasma metanephrines 1

Critical Pitfall to Avoid

Do not assume the adenoma is non-functioning without proper biochemical testing. Up to 50% of patients with primary aldosteronism are normokalaemic, and the only clue may be a suppressed plasma renin despite hypertension 1, 3. The patient described should have:

• Morning aldosterone and renin activity measured simultaneously after being seated for 5-15 minutes 1, 2
• Patient should be potassium-replete before testing, as hypokalemia suppresses aldosterone production 2, 4
• Ideally discontinue interfering medications (beta-blockers, diuretics) when clinically feasible, or interpret results in context 1, 2

Expected Findings in This Clinical Scenario

For a confirmed non-functioning 1.5 cm adenoma with hypertension:

• PRA: Normal to elevated (0.5-4.0 ng/mL/hr), depending on antihypertensive medications 2
• Plasma aldosterone: Normal (typically <15 ng/dL) 2
• ARR: <20-30 (normal range) 1, 2
• Serum potassium: Normal 1

If renin were suppressed (<0.5 ng/mL/hr) with elevated or high-normal aldosterone, this would suggest the adenoma is actually functioning (producing aldosterone), requiring confirmatory testing with saline suppression or oral sodium loading 1, 2. In such cases, adrenal vein sampling would be needed to determine lateralization before considering adrenalectomy 1.

Management Implications

For a truly non-functioning adenoma of 1.5 cm 1:

• No surgical intervention required for the adenoma itself
• Repeat imaging in 6-12 months, then annually if stable 1
• Annual hormonal screening for 4-5 years to detect development of autonomous function 1
• Treat hypertension with standard antihypertensive therapy as the adenoma is not the cause 1