What is the best study to evaluate for renal hypertension?

Best Study to Evaluate for Renal Hypertension

For patients with normal renal function (eGFR ≥30 mL/min/1.73 m²), CT angiography (CTA) or MR angiography (MRA) are the preferred imaging modalities, with CTA and MRA showing sensitivities of 88-100% and specificities of 71-100% for detecting renal artery stenosis. 1 For patients with severely impaired renal function (eGFR <30 mL/min/1.73 m²), duplex Doppler ultrasound is the preferred initial screening examination. 1

Initial Clinical Assessment

Before ordering imaging studies, confirm high clinical suspicion based on specific features:

• Age criteria: New-onset hypertension in patients <35 years or sudden onset/worsening after age 50 1
• Treatment resistance: Refractory hypertension despite multiple medications 1
• Medication response: Deterioration of renal function after starting ACE inhibitors or ARBs 1
• Associated conditions: Generalized atherosclerotic disease with hypertension, flash pulmonary edema 1
• Physical findings: Abdominal bruits, asymmetric kidney size on imaging 1

Imaging Algorithm Based on Renal Function

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

First-line options (choose based on local expertise and availability):

• Contrast-enhanced CTA: Sensitivity 88-100%, specificity 71-100% for detecting renal artery stenosis >50% 1
• Gadolinium-enhanced MRA: Sensitivity 97%, specificity 85% in meta-analysis of 25 studies 1
• Duplex Doppler ultrasound: Useful when operators are highly experienced, though time-consuming and operator-dependent 1

Key advantages of CTA/MRA over ultrasound:

• Can assess accessory renal arteries, aortic disease, and other causes of secondary hypertension (pheochromocytomas) 1
• Not affected by bilateral renovascular disease 1
• More reliable for less experienced operators 1
• Better visualization in patients with obesity or bowel gas 1

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

Duplex Doppler ultrasound is the preferred screening examination (rated 9/9 in appropriateness by ACR) 1, 2

Ultrasound diagnostic criteria:

• Peak systolic velocity (PSV) ≥200 cm/s (sensitivity 73-91%, specificity 75-96%) 1
• Renal artery to aortic ratio (RAR) ≥3.5 1
• Parvus-tardus intrarenal waveform with acceleration time >70 milliseconds 1

Alternative for eGFR <30 mL/min/1.73 m²:

• Non-contrast MRA using steady-state free precession (SSFP) techniques (rated 7/9 in appropriateness) 1, 2
• Avoids both iodinated contrast (CIN risk) and gadolinium (NSF risk) 1

For Borderline Renal Function (eGFR 30-45 mL/min/1.73 m²)

CTA can be performed with appropriate precautions: 1, 2

• Minimize contrast volume (keep total contrast volume/eGFR <3.4) 2
• Provide hydration with isotonic saline before and after procedure 2
• Consider iso-osmolar contrast media (iodixanol) rather than low-osmolar agents 2
• Monitor serum creatinine 48-72 hours post-procedure 2

Modalities to Avoid or Use Selectively

Captopril Renal Scintigraphy

• Mean sensitivity only 81% with range 34-93% 1
• Decreased accuracy in bilateral stenosis, impaired renal function, and urinary obstruction 1
• Poor predictive value for response to revascularization (positive predictive value as low as 51%) 1
• Limited role: May assess physiologic significance of known stenosis and relative kidney function before intervention 1

Renal Vein Renin Assays

• High false-positive rate (39-47.8%) and high false-negative rate (71%) 1
• Poor specificity (29-42%) despite reasonable sensitivity (65-92%) 1
• Not recommended as screening test for renovascular hypertension 1

Conventional Angiography

• Reserved for confirmation and intervention, not screening 1
• Should not be performed without suspicious noninvasive imaging 1

Essential Baseline Laboratory Testing

Before imaging, obtain: 1

• Serum creatinine and eGFR (using race-free CKD-EPI equation) 1
• Urinalysis with albumin-to-creatinine ratio 1
• Basic metabolic profile (sodium, potassium) 1
• Morning plasma aldosterone and plasma renin activity (to screen for primary aldosteronism) 1

Common Pitfalls to Avoid

• Using serum creatinine alone rather than eGFR for risk assessment—eGFR is superior for determining baseline renal function 1, 2
• Ordering ultrasound at centers without dedicated, experienced technologists—this highly operator-dependent technique requires expertise 1
• Failing to hydrate patients with borderline renal function before contrast administration 2
• Relying on captopril scintigraphy in patients with bilateral disease or impaired renal function where accuracy is significantly reduced 1
• Performing renal vein renin sampling as a screening test given its poor specificity and high false-positive rate 1

Additional Imaging Considerations

Renal ultrasound (non-Doppler) should be considered in hypertensive patients with CKD to assess kidney structure, determine causes of CKD, and exclude renoparenchymal disease 1

For young patients (<35 years), imaging is particularly important to detect fibromuscular dysplasia, which presents differently than atherosclerotic disease 1