Nephrology evaluation · KIMS Secunderabad
Renal Artery Stenosis — When Narrowed Arteries Drive Hypertension and Kidney Decline
Renal artery stenosis (RAS) is the narrowing of one or both of the arteries that supply blood to the kidneys. It is one of the most important correctable causes of secondary hypertension — hypertension driven by a specific, identifiable disease process rather than the more common essential hypertension. In a patient with RAS, blood pressure that has been difficult to control despite three or more antihypertensive medications — or blood pressure that was previously well-controlled but has suddenly become resistant — may have its root cause in a narrowed renal artery. Identifying and treating RAS in the right patient can reduce blood pressure significantly and protect kidney function from the progressive ischaemic damage that the stenosis causes.
RAS is found in approximately 1 to 5% of the hypertensive population — a small percentage overall, but a large absolute number given the enormous prevalence of hypertension in India. The two main causes are atherosclerosis (by far the most common, accounting for 90% of cases) and fibromuscular dysplasia (FMD — a non-inflammatory, non-atherosclerotic arterial disease predominantly affecting younger women). Each has a different clinical profile, natural history, and response to intervention.
How renal artery stenosis causes hypertension and kidney damage
The kidney is both the target and the driver of hypertension in RAS — a vicious cycle that makes the condition important to identify before it becomes self-perpetuating.
The renovascular hypertension mechanism. When renal perfusion pressure falls due to stenosis in the renal artery, the kidney interprets this as a signal of systemic hypotension — and responds by activating the renin-angiotensin-aldosterone system (RAAS). Renin is released from the juxtaglomerular apparatus, converting angiotensinogen to angiotensin I, which is then converted to angiotensin II — a potent vasoconstrictor. Angiotensin II raises systemic blood pressure, stimulates aldosterone release (causing sodium and water retention), and vasoconstricts the efferent arteriole to maintain glomerular filtration pressure in the affected kidney. The result is systemic hypertension driven by an inappropriately activated RAAS — classic renovascular hypertension.
Ischaemic nephropathy. In bilateral RAS or RAS in a solitary functioning kidney, the reduced perfusion causes progressive ischaemic damage to the kidney parenchyma — tubular atrophy, interstitial fibrosis, and ultimately cortical loss. This ischaemic nephropathy results in declining eGFR, which may be misattributed to hypertensive nephrosclerosis or diabetic nephropathy unless RAS is specifically investigated. The critical clinical clue: eGFR that falls acutely when an ACE inhibitor or ARB is started in a patient with unrecognised bilateral RAS — because these drugs dilate the efferent arteriole and reduce the compensatory glomerular pressure that was maintaining filtration in the ischaemic kidney.
Clinical clues suggesting renal artery stenosis
RAS rarely produces symptoms of its own — it is identified by the pattern of hypertension, kidney function changes, and associated findings that point to a renovascular cause. The clues below, particularly when several appear together, should prompt renal Doppler ultrasound and imaging of the renal arteries.
Features that should trigger renal artery stenosis evaluation
Any one of the following — and especially several together — warrants renal Doppler ultrasound and consideration of CT angiography or MR angiography:
Resistant hypertension (BP uncontrolled on 3+ antihypertensives including a diuretic) — RAAS overactivation is the underlying mechanism and is not responsive to standard antihypertensives alone.
Sudden worsening of previously controlled hypertension — new atherosclerotic plaque progression or FMD progression narrowing the artery further.
Acute kidney injury when ACE inhibitor or ARB is started — the classic sign of bilateral RAS or RAS in a solitary kidney; efferent arteriole dilation removes the compensatory pressure maintaining GFR.
Flash pulmonary oedema without cardiac explanation — bilateral RAS causing sudden volume overload (the Pickering syndrome). Highly specific for bilateral RAS.
Hypertension onset before age 30 (especially women) — FMD is the predominant cause of RAS in young women. Onset before 30 should always prompt FMD evaluation.
Abdominal bruit over the renal arteries — turbulent flow through the stenosis may produce an audible bruit in the epigastrium or flank — present in approximately 50% of cases.
Asymmetric kidney size on ultrasound — the kidney downstream of a significant stenosis gradually atrophies from ischaemia. Size difference of more than 1.5 cm between kidneys suggests ipsilateral RAS.
Hypokalaemia with resistant hypertension — excess aldosterone production driven by RAAS activation causes potassium wasting.
Causes — atherosclerotic vs fibromuscular dysplasia
Two distinct disease processes account for almost all RAS — and they differ in age and sex distribution, anatomy of the stenosis, systemic implications, and response to revascularisation.
Atherosclerotic RAS (90% of cases)
Atheromatous plaque narrows the ostium or proximal renal artery — typically in patients above 55 with established cardiovascular risk factors (hypertension, diabetes, dyslipidaemia, smoking). Atherosclerotic RAS is a marker of systemic atherosclerosis — these patients have an elevated risk of coronary artery disease and stroke that must be addressed alongside the renal artery disease. The stenosis tends to be at the ostium of the renal artery (where it originates from the aorta) and is often bilateral.
Fibromuscular dysplasia (FMD, 10% of cases)
A non-inflammatory, non-atherosclerotic arterial disease that affects the media or adventitia of the renal artery — causing the characteristic 'string of beads' appearance on angiography. FMD predominantly affects women (90% of cases) between the ages of 15 and 50. It does not cause the cardiovascular risk of atherosclerotic RAS and responds very well to percutaneous transluminal angioplasty (PTA) without stenting — cure rates for hypertension approach 50% in young women with FMD treated by PTA.
Diagnosis at KIMS
Renal Doppler ultrasound — first-line non-invasive test
Measures peak systolic velocity in the renal artery (above 200 cm/s suggests significant stenosis) and the resistive index within the kidney (elevated RI suggests intrarenal disease). Sensitive for main renal artery stenosis but less reliable for accessory renal arteries.
CT angiography (CTA)
High sensitivity and specificity for RAS. Provides excellent anatomical detail of the renal arteries, aorta, and parenchyma in a single study. Contrast required — caution in patients with reduced eGFR.
MR angiography (MRA)
Gadolinium-enhanced MRA is an alternative to CTA, particularly in patients with reduced eGFR. Does not require iodinated contrast. Slightly lower spatial resolution than CTA.
Captopril renogram (nuclear medicine)
Assesses the functional significance of stenosis rather than anatomy. A positive test (significant asymmetry of kidney function between sides after captopril administration) suggests functionally significant RAS.
Digital subtraction angiography (DSA) — the gold standard
Performed at the time of planned intervention (angioplasty or stenting) to confirm the anatomy and degree of stenosis. DSA also allows measurement of the translesional pressure gradient — a gradient above 20 mmHg indicates haemodynamic significance.
Treatment — not all RAS requires intervention
The decision to intervene in RAS is more nuanced than it appears. The ASTRAL (2009) and CORAL (2014) randomised trials found that renal artery stenting in patients with atherosclerotic RAS provided no significant benefit over optimal medical therapy alone in terms of blood pressure control or kidney function preservation in the average patient. This does not mean RAS should never be intervened upon — it means patient selection is critical.
Optimal medical therapy (all patients)
ACE inhibitors or ARBs (after confirming no bilateral RAS) · Statins · Aspirin · Blood pressure targets below 130/80. Addresses both the hypertension and the cardiovascular risk of atherosclerotic disease.
Percutaneous transluminal angioplasty (PTA) without stenting
First choice for FMD — cure rates for hypertension up to 50% in young women. Also used for short focal non-ostial atherosclerotic lesions.
Renal artery stenting (PTA + stent)
Atherosclerotic ostial stenosis — stenting prevents elastic recoil. Selected patients: flash pulmonary oedema (bilateral RAS), ACE inhibitor-induced AKI, rapidly declining eGFR with haemodynamically significant bilateral RAS, uncontrolled hypertension despite 4+ medications.
Surgical revascularisation
Rare — reserved for complex anatomical situations not amenable to percutaneous treatment. Aorto-renal bypass or ex vivo repair.
Book a Hypertension and Kidney Artery Assessment at KIMS
Frequently Asked Questions — Renal Artery Stenosis
Yes — bilateral renal artery stenosis or stenosis in a solitary functioning kidney causes ischaemic nephropathy — progressive kidney damage from reduced blood supply — that can progress to end-stage renal disease if untreated. The decline in eGFR is typically slow and may be misattributed to other causes (hypertensive nephrosclerosis, diabetic nephropathy) unless RAS is specifically investigated. The clue is an acute, disproportionate fall in eGFR when an ACE inhibitor or ARB is started — this is virtually diagnostic of bilateral haemodynamically significant RAS and should prompt immediate investigation.
Related but not identical. Renal artery stenosis is the anatomical finding — narrowing of the renal artery. Renovascular hypertension is the clinical consequence — hypertension driven by the RAAS activation that the stenosis triggers. Not all anatomically significant RAS causes renovascular hypertension, and the degree of hypertension response to revascularisation varies. A functionally significant stenosis — one that activates RAAS and drives blood pressure — can be confirmed by captopril renography or by measuring the translesional pressure gradient at angiography (a gradient above 20 mmHg indicates haemodynamic significance).
ACE inhibitors and ARBs should be used with caution in patients with confirmed bilateral RAS or RAS in a solitary functioning kidney — because they reduce the efferent arteriolar tone that compensates for reduced perfusion, potentially causing acute kidney injury. However, ACE inhibitors are not absolutely contraindicated in unilateral RAS with a normal contralateral kidney — where the healthy kidney can compensate. The critical point: if eGFR falls more than 25 to 30% from baseline within 2 to 4 weeks of starting an ACE inhibitor or ARB, bilateral RAS must be excluded. This ACE inhibitor-induced AKI is one of the most reliable clinical clues pointing to bilateral haemodynamically significant RAS.
Atherosclerotic RAS: men and women above 55 with established cardiovascular risk factors — hypertension (especially longstanding and difficult to control), diabetes, dyslipidaemia, smoking, and established coronary or peripheral artery disease. The presence of peripheral artery disease or carotid artery stenosis substantially increases the probability of RAS. Fibromuscular dysplasia (FMD): women aged 15 to 50 with onset of hypertension before age 30, without conventional cardiovascular risk factors. FMD should be excluded in every young woman with new-onset hypertension — it is the most common correctable cause of hypertension in this demographic.
In atherosclerotic RAS, the evidence from the ASTRAL and CORAL trials shows that stenting does not cure hypertension in most patients and provides only modest blood pressure improvement compared to optimal medical therapy alone. This is partly because atherosclerotic RAS patients often have concurrent essential hypertension from years of elevated blood pressure causing vascular remodelling — independent of the RAS. Stenting is most beneficial for specific indications (flash pulmonary oedema, ACE inhibitor-induced AKI, rapidly declining eGFR). In FMD, angioplasty without stenting is highly effective — cure or significant improvement of hypertension occurs in 50 to 80% of patients, particularly young women treated early.
FMD is a non-inflammatory arterial disease of unknown cause — it is not driven by cholesterol plaque or cardiovascular risk factors. It primarily affects the media of the renal artery (medial FMD — the most common type), causing alternating areas of thinning and thickening that produce the classic 'string of beads' appearance on angiography. FMD affects young women almost exclusively, does not carry the cardiovascular risk of atherosclerotic disease, and responds very well to angioplasty. It can also affect the carotid and vertebral arteries — causing cervical artery dissection and stroke — which makes FMD evaluation relevant beyond the kidneys.
No blood test directly confirms RAS — imaging is required. However, blood tests can suggest that RAS may be the cause of resistant hypertension: elevated plasma renin activity (PRA) with suppressed aldosterone suggests RAAS overactivation from RAS; hypokalaemia and elevated aldosterone suggest secondary hyperaldosteronism driven by RAS; rising creatinine after starting an ACE inhibitor is highly suggestive of bilateral haemodynamically significant RAS. The Doppler ultrasound, CTA, or MRA is then used to confirm the anatomy.
KIMS Secunderabad — Dr. V. S. Reddy (Senior Consultant Nephrologist, 20+ years), complete RAS workup including renal Doppler, CT angiography, captopril renography, and coordination with interventional radiology for angioplasty and stenting in selected cases. Optimal medical therapy protocol including RAAS blockade, statin, and cardiovascular risk management. NABH and NABL accredited. Call 040-4488-5000.