What is the appropriate workup and management for a patient with suspected renovascular hypertension?

Workup for Renovascular Hypertension

The workup for renovascular hypertension should begin with clinical risk stratification, followed by imaging with either MRA with contrast, CTA with contrast, or duplex Doppler ultrasound in patients with normal renal function, while duplex ultrasound is preferred in those with impaired renal function (eGFR <30 mL/min/1.73 m²). 1

Clinical Features Suggesting Renovascular Hypertension

Suspect renovascular hypertension when specific clinical features are present, as these increase the likelihood of finding functionally significant disease 1:

• Abdominal bruit (particularly epigastric or upper abdominal) 1
• Age-related patterns: onset before age 35 or new onset after age 50 1
• Severe hypertension: diastolic BP >110 mmHg, malignant or accelerated hypertension 1
• Refractory hypertension despite multiple medications 1
• Acute kidney injury after starting ACE inhibitors or ARBs 1
• Discrepant kidney sizes on imaging 1
• Generalized atherosclerotic disease with hypertension 1
• Hypokalemia on screening laboratories 1

Laboratory Evaluation

Initial laboratory workup should include 1:

• Serum creatinine and eGFR to assess renal function
• Serum potassium (hypokalemia may suggest secondary aldosteronism from renal ischemia)
• Plasma renin levels: Very elevated renin raises suspicion for renovascular hypertension, though sensitivity is limited 1

Important caveat: While elevated renin supports the diagnosis, normal renin does not exclude renovascular hypertension, as renin levels have poor sensitivity 1, 2.

Imaging Strategy Based on Renal Function

For Patients with Normal Renal Function (eGFR ≥30 mL/min/1.73 m²)

The preferred imaging modalities are 1:

1. MRA abdomen with and without IV contrast (rating 8/9 - usually appropriate)
2. CTA abdomen with IV contrast (rating 8/9 - usually appropriate)
3. Duplex Doppler ultrasound of kidneys (rating 7/9 - usually appropriate)

MRA and CTA are equally effective and the choice depends on local expertise, availability, and patient factors (claustrophobia, contrast allergies) 1.

For Patients with Impaired Renal Function (eGFR <30 mL/min/1.73 m²)

Duplex Doppler ultrasound is the first-line imaging modality (rating 9/9 - usually appropriate) 1:

• Avoids contrast-related complications (nephrogenic systemic fibrosis with gadolinium, contrast-induced nephropathy with iodinated contrast) 1
• Should include bilateral assessment of renal arterial resistive index 1
• Limitation: Sensitivity and specificity vary considerably between laboratories and depend heavily on operator expertise 2

Non-contrast MRA is an alternative (rating 7/9) if ultrasound is non-diagnostic 1.

Additional Imaging Considerations

When Fibromuscular Dysplasia is Suspected

CT or MRI angiography from head to pelvis is recommended, as fibromuscular dysplasia is a systemic disease that can affect multiple vascular beds 1.

Role of Functional Testing

• Tc-99m ACE-inhibitor renography has limited utility (rating 5/9 in normal renal function, 3/9 in impaired function) 1
• Captopril-stimulated peripheral renin activity may be useful for screening in unselected populations (38% positive predictive value, 92% negative predictive value in high-risk groups) 3
• Functional tests do not accurately predict which patients will respond to revascularization 3

Invasive Procedures

Conventional angiography and renal vein sampling are generally not appropriate for initial diagnosis (rating 3/9) 1:

• Reserved for confirmation when non-invasive tests are equivocal
• Primarily used when intervention (angioplasty/stenting) is planned at the same time 1, 4

Critical Distinction: Bystander Stenosis vs. Functionally Significant Disease

A key pitfall is identifying anatomic stenosis without functional significance 1:

• Renal artery stenosis may be present in patients with essential hypertension without causing renovascular hypertension
• Stenosis must exceed 70-75% to reduce perfusion pressure and activate the renin-angiotensin system 1
• The ultimate criterion for renovascular hypertension is blood pressure improvement after intervention 1

Special Populations

Children and Adolescents

Suspect renovascular hypertension in pediatric patients with 1:

• Stage 2 hypertension
• Significant diastolic hypertension
• Discrepant kidney sizes on ultrasound
• Hypokalemia
• Epigastric or upper abdominal bruit

Pregnant Women

In pregnant women with suspected hypertensive emergency, include 1:

• Renal ultrasound for renal parenchymal disease
• Duplex renal artery Doppler for renovascular disease
• Avoid contrast-enhanced studies when possible

Algorithmic Approach

1. Identify clinical features suggesting renovascular hypertension (abdominal bruit, age pattern, severe/refractory hypertension, ACE inhibitor-induced AKI)
2. Check baseline labs: creatinine, eGFR, potassium, renin (if available)
3. Select imaging based on renal function:
   • eGFR ≥30: MRA with contrast, CTA with contrast, or duplex ultrasound
   • eGFR <30: Duplex ultrasound first-line, non-contrast MRA if non-diagnostic
4. If fibromuscular dysplasia suspected: Extend imaging from head to pelvis
5. Reserve angiography for cases requiring intervention or when non-invasive tests are inconclusive