Renal · Renovascular HTN

Renovascular Hypertension

Snapshot

Renovascular hypertension (RVH) is high blood pressure driven by reduced renal perfusion — almost always renal-artery stenosis — which activates the renin–angiotensin–aldosterone system (RAAS). It is an important correctable cause of secondary hypertension (primary aldosteronism is more common). Anatomical imaging confirms the stenosis (Duplex ultrasound first-line, then CT or MR angiography); ACE-inhibitor (captopril) renography is a functional test with a narrower, selective role today.

RAASRenin-driven

ARAS ~90%Commonest cause

Duplex USFirst-line imaging

ACE-I renographyFunctional test

Reference values

⁹⁹ᵐTc-MAG3 (tubular; preferred if creatinine is raised) or ⁹⁹ᵐTc-DTPA (glomerular filtration); 1-day protocol: ~40 MBq baseline, then 200–400 MBq for the ACE-I study.
ACE-inhibition: captopril 25–50 mg orally 1 h before tracer (fasting for absorption); or enalaprilat 40 µg/kg IV (max 2.5 mg) over 3–5 min, image ~15 min later.
Stop ACE-inhibitor/ARB before the study (captopril 3 days; longer-acting agents 5–7 days); stop chronic diuretics if possible; hydrate; monitor blood pressure.
Duplex US: peak systolic velocity ≥180–200 cm/s (criteria vary by laboratory) suggests ≥60% stenosis; resistive index >0.8 predicts poor revascularisation response.
Anatomical accuracy: CT angiography and gadolinium-enhanced MR angiography performed best in meta-analysis, better than ultrasound and captopril renography (Vasbinder et al., Ann Intern Med 2001).
ACE-I renography: sensitivity and specificity ~90% when creatinine is <1.7 mg/dL, lower in azotaemia; a normal study means <10% probability of RVH.
High-probability ACE-I renogram = ACE-I-induced deterioration of the affected kidney: MAG3 unilateral parenchymal retention (20-min/peak ratio rise ≥0.15, Tmax prolonged ≥2–3 min or ≥40%, or worsened curve grade); DTPA relative uptake falls >10%.

Diagram of a glomerulus downstream of a renal-artery stenosis: angiotensin II constricts the efferent arteriole to keep filtration going, and after an ACE-inhibitor the efferent relaxes, filtration falls and the renogram worsens. — Figure. Why ACE-inhibitor renography works: behind a haemodynamically significant renal-artery stenosis, angiotensin II constricts the efferent arteriole and preserves GFR; blocking it lowers glomerular pressure, so the affected kidney’s renogram worsens (MAG3 cortical retention and later Tmax, or a fall in DTPA relative uptake).

Flowchart for suspected renovascular hypertension: clinical clues lead to Duplex ultrasound, then CT or MR angiography, and ACE-inhibitor renography only when the significance of a stenosis is uncertain, with high, intermediate and low probability outcomes. — Figure. Investigation pathway for suspected renovascular hypertension: anatomy is confirmed by Duplex ultrasound, then CT or MR angiography; ACE-inhibitor renography is reserved for judging the functional significance or laterality of a stenosis, and its result is graded as high (>90%), intermediate or low (<10%) probability (after the SNM renovascular hypertension guideline v3.0 and the ACR Appropriateness Criteria 2017).

Definition

Hypertension caused by a haemodynamically significant reduction in renal blood flow, usually from stenosis of the main renal artery (or a branch).
‘Renal-artery stenosis’ is the anatomical lesion; ‘renovascular hypertension’ is the clinical syndrome it produces — the two are not synonymous (many stenoses are incidental and not causing the hypertension).
It is an important potentially reversible cause of secondary hypertension (primary aldosteronism is more common).

Pathophysiology

Renal-artery stenosis lowers perfusion pressure to the affected kidney.
Juxtaglomerular cells release renin → angiotensin II (vasoconstriction) and aldosterone (sodium and water retention) → the RAAS raises blood pressure.
Angiotensin II constricts the efferent arteriole to preserve glomerular filtration in the stenotic kidney — the physiological basis of ACE-inhibitor renography (blocking it drops that kidney’s GFR and worsens its renogram).
Unilateral disease is renin-dependent and potentially curable; with bilateral disease or a stenosis to a solitary kidney, ACE-inhibitors/ARBs can precipitate acute kidney injury.

Causes

Cause	Frequency / typical profile	Features
Atherosclerotic renal-artery stenosis (ARAS)	~90% of RVH; older (>55–65), cardiovascular risk factors	Ostial/proximal stenosis; progressive; often bilateral
Fibromuscular dysplasia (FMD)	~10%; young women (15–50)	Mid/distal artery, classic “string of beads”; often curable by angioplasty
Other (uncommon)	Any age	Vasculitis (Takayasu), dissection/thrombosis/infarction, radiation fibrosis, extrinsic compression, mid-aortic syndrome, transplant renal-artery stenosis

When should renovascular hypertension be suspected?

Hypertension onset before ~30 years (suggests FMD) or new/accelerating after ~55 years (suggests ARAS).
Resistant hypertension — uncontrolled on ≥3 agents including a diuretic — or accelerated/malignant hypertension.
A rise in serum creatinine >30% after starting an ACE-inhibitor or ARB.
Recurrent ‘flash’ pulmonary oedema or unexplained heart failure.
Abdominal or flank bruit; unexplained hypokalaemia with metabolic alkalosis.
Asymmetric kidney size / an unexplained small kidney; unexplained renal impairment; widespread atherosclerosis.

Tests available & investigation of choice

Diagnosis is confirmed anatomically; functional testing is selective. Figures are cohort-dependent.

Test	Sensitivity	Specificity	Role
Duplex ultrasound	High	High	First-line screen; PSV ≥180–200 cm/s (lab-dependent) suggests ≥60% stenosis; resistive index >0.8 predicts poor response to revascularisation
CT angiography	High	High	Anatomical investigation of choice when US is equivocal; needs iodinated contrast and radiation
MR angiography	High	High	Anatomy without radiation; tends to over-estimate stenosis; with eGFR <30 use a group II gadolinium agent only when needed (very low NSF risk)
Catheter angiography (DSA)	Gold standard	—	Definitive; used when non-invasive tests conflict, or at the time of intervention
ACE-inhibitor (captopril) renography	≈90% (lower if azotaemic)	≈90%	Functional test / lateralisation — selective role; less sensitive, radiation, time-consuming

Where captopril renography stands in the pathway

It is no longer a first-line test — anatomical imaging (Duplex → CT/MR angiography) has largely replaced it for detecting stenosis.
Practice shifted after the ASTRAL (2009) and CORAL (2014) trials, which showed renal-artery stenting adds little to optimal medical therapy in atherosclerotic disease — so proving ‘functional significance’ is less often decisive.
Selective current roles: judging the haemodynamic significance and lateralising renin production when anatomy is borderline; helping decide whether a stenosis is worth treating (e.g. angioplasty in FMD, or before revascularisation); and when iodinated/gadolinium contrast is contraindicated.
Note: for renovascular hypertension the nuclear test is ACE-inhibitor (captopril) renography — not diuretic renography, which is used for suspected obstruction.

Tracers, doses & protocol

⁹⁹ᵐTc-MAG3 is preferred (high tubular extraction, better in impaired function); ⁹⁹ᵐTc-DTPA (filtration) is an alternative.
Give the ACE-inhibitor: captopril 25–50 mg orally 1 h before the tracer (patient fasting), or enalaprilat 40 µg/kg IV (max 2.5 mg) over 3–5 min with imaging ~15 min later.
Withhold ACE-inhibitors/ARBs beforehand, stop diuretics, and hydrate well; monitor blood pressure (risk of hypotension after ACE-I).
Two-day protocol: ACE-I study first, with a baseline study only if it is abnormal. One-day protocol: low-activity (~40 MBq) baseline first, then the ACE-I study (200–400 MBq).

Interpretation — criteria for a positive scan

Compare the post-ACE-I renogram with baseline: a functionally significant stenosis shows ACE-I-induced deterioration of the affected kidney.
⁹⁹ᵐTc-MAG3 (tubular): worsening of the renogram curve grade; prolonged time-to-peak (Tmax) — an increase of ≥2–3 min or ≥40%; a rise in the parenchymal 20-min/peak ratio of ≥0.15 — unilateral parenchymal retention is the key criterion.
⁹⁹ᵐTc-DTPA (filtration): a fall in the affected kidney’s relative (split) function of >10% after ACE-inhibition.
Standardised probability: high (>90%) = marked unilateral ACE-I-induced change; low (<10%) = normal ACE-I study; intermediate = abnormal baseline (e.g. small kidney with <30% uptake) unchanged after ACE-I.
A normal ACE-inhibitor renogram makes renovascular hypertension unlikely; a high-probability study supports a renin-dependent, potentially treatable lesion.

Common pitfalls

Bilateral stenosis, a stenosis to a solitary kidney, and significant renal impairment reduce sensitivity and cause false negatives.
Ongoing ACE-inhibitor/ARB therapy slightly lowers sensitivity; dehydration or chronic diuretics lower specificity (bilateral symmetrical changes); poor captopril absorption (solid food within 4 h) can invalidate an oral study.
The test reflects functional significance, not anatomy — always correlate with angiographic imaging.
Watch for symptomatic hypotension after ACE-inhibition — monitor and hydrate; use caution in volume-depleted patients.

Conclusion

Renovascular hypertension is an important correctable cause of secondary hypertension — suspect it from the clinical clues above.
Confirm the stenosis with Duplex ultrasound first, then CT or MR angiography; catheter angiography is definitive.
ACE-inhibitor (captopril) renography is now a selective functional test — most useful to show whether a stenosis is haemodynamically significant or lateralising, particularly when revascularisation (e.g. angioplasty for FMD) is being considered.

Sources

Regalla DKR et al. Renovascular Hypertension. StatPearls (NCBI Bookshelf NBK551587).
ACR Appropriateness Criteria® Renovascular Hypertension. J Am Coll Radiol 2017;14:S540–S549.
Taylor AT et al. SNM procedure guideline for diagnosis of renovascular hypertension, v3.0 (2003); Taylor A et al. Consensus report on ACE inhibitor renography. J Nucl Med 1996;37:1876–1882.
ASTRAL Investigators. N Engl J Med 2009;361:1953–1962; Cooper CJ et al. (CORAL). N Engl J Med 2014;370:13–22; Vasbinder GB et al. Ann Intern Med 2001;135:401–411; Radermacher J et al. N Engl J Med 2001;344:410–417; 2024 ESC hypertension guidelines, Eur Heart J 2024;45:3912–4018.

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