Resistant hypertension means blood pressure above target — under the 2025 AHA/ACC guideline that target is below 130/80 for nearly everyone — despite three medications at optimal doses, one of which is a diuretic. Or blood pressure at target, but requiring four or more drugs to hold it there.
It is a nephrology problem because the kidney sets blood pressure, and because the causes worth finding are the ones the kidney explains.
First: is it actually resistant?
A large share of apparent resistance is not resistance at all. Before adding a fourth drug, three things get ruled out.
White coat effect. Roughly one in five people with high office readings have normal pressures elsewhere. Twenty-four-hour ambulatory monitoring is the only way to know, and it is the first thing we do. Adding medication to a patient whose pressure is normal at home means side effects with no benefit.
Non-adherence. Not a character flaw. Four pills a day with side effects is genuinely hard, and it is the most common reason regimens fail. We ask directly and without judgment, because the answer changes everything.
The regimen itself. Wrong diuretic, wrong dose, wrong timing. Chlorthalidone outperforms hydrochlorothiazide and is prescribed less often. Patients with reduced kidney function need a loop diuretic, not a thiazide, and are frequently on the wrong one.
What is causing it
Secondary causes are found in a meaningful fraction of true resistant hypertension, and each has a specific treatment.
| Secondary Cause | Notes | Common Clue |
|---|---|---|
| Primary aldosteronism | is the most common and the most missed. It is far more prevalent than the textbooks once suggested, and it is screened for with a plasma aldosterone-to-renin ratio. Anyone with resistant hypertension should have this test. Most have not. | Low potassium with high aldosterone |
| Obstructive sleep apnea | strongly associated, frequently undiagnosed. | Loud snoring, daytime fatigue |
| Renal artery stenosis (narrowing of kidney artery) | particularly with a sudden rise in creatinine after starting an ACE inhibitor or ARB. | Sudden rise, flash pulmonary edema |
| Chronic kidney disease | which both causes resistant hypertension and results from it. | Reduced eGFR, protein in the urine |
| Medications | NSAIDs, decongestants, oral contraceptives, stimulants. | |
| Pheochromocytoma, Cushing's syndrome, thyroid disease, and coarctation | rare, but each has a specific fix. |
Treatment
The fourth drug, when one is genuinely needed, is usually spironolactone. It outperforms other options in resistant hypertension by a wide margin, which reflects how often unrecognized aldosterone excess is driving the problem. It requires potassium monitoring, particularly in kidney disease.
Sodium restriction matters more here than in ordinary hypertension. Many patients with resistant hypertension are salt-sensitive, and the effect of reducing intake is substantial.
Weight loss, alcohol reduction, treating sleep apnea, and stopping the offending medication all move the number.
Why the nighttime reading matters
Blood pressure should fall ten to twenty percent during sleep. Many patients with resistant hypertension and chronic kidney disease do not dip, and some rise overnight.
Non-dipping independently predicts kidney disease progression and cardiovascular events. It cannot be detected in a daytime office visit. Finding it often changes when we tell you to take your medication — a change that costs nothing and matters considerably.