What is the best initial diagnostic investigation for a female patient with refractory hypertension, obesity, and a renal bruit (abnormal sound heard over the kidney)?

Diagnostic Investigation for Suspected Renovascular Hypertension

Renal Doppler ultrasound (Option A) is the recommended initial diagnostic investigation for this patient with refractory hypertension, obesity, and renal bruit. 1, 2

Rationale for Doppler Ultrasound as First-Line

The presence of a renal bruit in a patient with refractory hypertension creates high clinical suspicion for renovascular disease, making screening imaging appropriate. 1, 2 The American College of Radiology specifically identifies abdominal bruits and treatment-resistant hypertension as key clinical features warranting investigation for renal artery stenosis. 1, 2

Doppler ultrasound is the preferred initial screening test because it:

• Is noninvasive and repeatable 1, 3
• Can be performed regardless of renal function status 1, 2
• Avoids radiation exposure 1
• Avoids contrast-related nephrotoxicity risk 1
• Has reasonable diagnostic accuracy with sensitivity of 67-90% and specificity of 84-90% for detecting >60% stenosis 1

Why CT Angiography is Not First-Line

While CT angiography (Option B) has excellent sensitivity (88-100%) and specificity (71-100%) for detecting renal artery stenosis 2, it should be reserved for patients with normal renal function (eGFR ≥30 mL/min/1.73 m²) or when ultrasound is nondiagnostic. 1, 2

CT is specifically recommended when:

• Body habitus limits ultrasound visualization (relevant in this obese patient) 1
• Doppler ultrasound is technically inadequate or equivocal 1
• The patient cannot cooperate with the time-consuming Doppler examination 1

Critical Caveats for Doppler Ultrasound

Obesity significantly limits ultrasound accuracy in this patient. 1 The examination is highly operator-dependent and requires dedicated, experienced technologists. 1, 2 If the ultrasound study is technically limited or nondiagnostic due to body habitus, proceed directly to CT angiography (assuming adequate renal function). 1, 2

Key Doppler criteria to assess:

• Peak systolic velocity >180-285 cm/s in the renal artery suggests >60% stenosis 1
• Renal-to-aortic ratio (RAR) >3.5 indicates significant stenosis 1
• Parvus-tardus waveform distally suggests proximal stenosis 1
• Resistive index >0.80 may predict poor response to revascularization 1

Essential Pre-Imaging Workup

Before any imaging, obtain:

• Serum creatinine and eGFR (using race-free CKD-EPI equation) 1, 2
• Urinalysis with albumin-to-creatinine ratio 1, 2
• Basic metabolic panel (sodium, potassium) 1, 2
• Morning plasma aldosterone and plasma renin activity to screen for primary aldosteronism 1, 2

This biochemical evaluation is critical because primary aldosteronism is a common cause of refractory hypertension and must be excluded. 1

Clinical Algorithm

1. Start with renal Doppler ultrasound as the initial screening test 1, 2
2. If ultrasound is technically adequate and negative, renovascular disease is unlikely—consider alternative causes of refractory hypertension 1
3. If ultrasound is positive or technically limited (likely in obesity), proceed to CT angiography for definitive diagnosis (if eGFR permits) 1, 2
4. If eGFR <30 mL/min/1.73 m², consider non-contrast MRA or proceed directly to angiography if intervention is planned 1, 2

Common Pitfalls to Avoid

• Do not skip ultrasound and go directly to CT unless there is severe obesity making ultrasound futile 1, 2
• Do not order ultrasound at centers without experienced vascular sonographers—this defeats the purpose of screening 1, 2
• Do not use serum creatinine alone—always calculate eGFR for proper risk stratification 2
• Do not forget to hydrate patients with borderline renal function before any contrast administration 2
• Do not rely on captopril scintigraphy—it has poor accuracy in bilateral disease and renal impairment 1, 2