Resistant Hypertension with Hypokalaemia: Interpreting the Aldosterone–Renin Ratio
A 52-year-old woman has persistent hypertension despite a verified three-drug regimen: amlodipine 10 mg, losartan 100 mg and chlorthalidone 25 mg daily. Home readings average 158/96 mmHg, and 24-hour ambulatory monitoring confirms a mean of 152/94 mmHg with loss of nocturnal dipping and no white-coat effect. Adherence is confirmed by pill counts and pharmacy refills. She has no symptoms of sleep apnoea, and renal artery imaging is normal. Laboratory results: sodium 143 mmol/L, potassium 3.0 mmol/L, bicarbonate 29 mmol/L, creatinine 0.9 mg/dL, plasma aldosterone 22 ng/dL, plasma renin activity 0.2 ng/mL/h, and a calculated aldosterone-to-renin ratio of 110. She is worried about kidney damage from spironolactone and asks whether the test result can be trusted and whether she needs surgery.
1. Interpret the aldosterone-to-renin ratio and list the confounders that could distort it. What will you do before repeating or acting on it?
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The ratio is positive, but it was measured under imperfect conditions. An aldosterone of 22 ng/dL with a suppressed renin of 0.2 ng/mL/h gives a ratio of 110, well above the usual threshold (ratio >30 with aldosterone >15 ng/dL), and spontaneous hypokalaemia with metabolic alkalosis supports primary aldosteronism.
Confounders to consider.
- Hypokalaemia itself suppresses aldosterone secretion, so the true value may be higher; correct potassium to at least 4.0 mmol/L before repeating.
- Mineralocorticoid receptor antagonists and ENaC blockers cause false-positive ratios and must be stopped 4–6 weeks beforehand; she is not taking one.
- Beta-blockers and central alpha-agonists suppress renin and cause false positives; ACE inhibitors, ARBs and diuretics raise renin and cause false negatives. She takes losartan, which would bias the ratio downward, yet renin is still suppressed - this strengthens rather than weakens the diagnosis.
- Confirm she is not using liquorice, NSAIDs or potassium-wasting supplements, and that the sample was taken mid-morning after sitting for 5–15 minutes.
Practical step. Correct potassium with oral potassium chloride, continue amlodipine (minimal effect on the ratio), standardise the sampling conditions and repeat the aldosterone and renin before moving to confirmatory testing. Do not order adrenal imaging on the basis of the ratio alone.
2. How would you confirm the diagnosis, and who needs adrenal vein sampling?
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Confirmation first. A positive screen is not a diagnosis. Options include the saline infusion test (2 L of 0.9% sodium chloride over 4 hours, with a post-infusion aldosterone above about 10 ng/dL confirming primary aldosteronism), the captopril challenge, oral sodium loading or fludrocortisone suppression. Saline infusion is widely used and safe here with normal renal function and no heart failure. Do not proceed to imaging before biochemical confirmation - an incidental adrenal nodule in a patient without primary aldosteronism is a common trap.
Then subtype. Once confirmed, adrenal CT identifies a unilateral mass and excludes a large or irregular lesion suspicious for adrenocortical carcinoma. CT alone cannot decide on surgery, because bilateral hyperplasia can mimic a nodule and small adenomas may be invisible.
Who needs adrenal vein sampling. Any patient who is a potential surgical candidate. She is 52, so she needs AVS to distinguish unilateral from bilateral disease. The main exception is a young patient (under about 35 years) with a clear unilateral hypodense adenoma and marked hypokalaemia, where some guidelines allow proceeding directly to surgery. AVS should be performed by an experienced operator with ACTH stimulation and successful cannulation confirmed by cortisol gradients; non-lateralising or failed sampling should be repeated rather than guessed at.
3. How does the management differ between unilateral and bilateral disease, and how would you counsel her about spironolactone and kidney risk?
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If AVS lateralises (unilateral disease). Laparoscopic adrenalectomy is the treatment of choice; roughly half of patients are cured of hypertension and nearly all improve. She needs preoperative potassium and BP control, usually with an MRA or amlodipine, and honest counselling that hypertension may persist if she already has established vascular disease.
If AVS shows bilateral disease, or she prefers medical therapy. Bilateral adrenal hyperplasia is treated with a mineralocorticoid receptor antagonist: spironolactone 12.5–25 mg daily titrated towards 100 mg, or eplerenone 25–50 mg if gynaecomastia or menstrual disturbance occurs. Expect BP to fall over 4–8 weeks and potassium to rise. Check potassium and creatinine at 1–2 weeks and again at 3 months, add a thiazide or amlodipine if needed, and advise avoidance of NSAIDs. MRA therapy also reduces the cardiovascular and renal damage caused by aldosterone excess.
Counselling about kidney damage. Her eGFR is normal; spironolactone does not damage the kidney. The real risk is hyperkalaemia, especially if renal function declines or she takes NSAIDs, potassium supplements or trimethoprim. With monitoring, the benefit of better BP control and fewer cardiovascular events clearly outweighs that risk. Tell her explicitly not to stop the drug on her own without a potassium check, and give her a written plan for sick days when the MRA should be temporarily withheld.