## Distinguishing Primary from Secondary Hypertension (RAS) ### Key Discriminating Feature **Key Point:** An abdominal systolic-diastolic bruit (or continuous bruit) is a hallmark finding of renal artery stenosis (RAS) and is absent in primary hypertension. This bruit reflects turbulent flow across the stenotic lesion. ### Why This Discriminates The presence of a vascular bruit is a **specific clinical sign** for RAS: - Heard best in the epigastrium or flank - Systolic-diastolic (continuous) pattern indicates significant stenosis - Sensitivity ~50–60%, but **high specificity** for RAS when present - Absent in primary hypertension (no structural vascular lesion) ### Comparison Table: Primary vs. Secondary (RAS) Hypertension | Feature | Primary Hypertension | RAS-Induced Hypertension | | --- | --- | --- | | **Abdominal bruit** | Absent | Present (systolic-diastolic) | | **Age of onset** | Usually >40 years | Can occur at any age; sudden onset suspicious | | **Renal function** | Normal initially | May be abnormal; asymmetric renal size | | **LVH** | Common (both have it) | Common (both have it) | | **Nocturnal dipping** | Often preserved | May be lost (both can lose it) | | **Plasma renin activity** | Low-normal | Elevated | **High-Yield:** The **abdominal bruit** is the single most useful bedside discriminator. Its presence should prompt imaging (duplex ultrasound, CT angiography, or MR angiography) to confirm RAS. ### Clinical Pearl A newly detected bruit in a patient with hypertension, especially if hypertension is sudden-onset or resistant to therapy, is a red flag for RAS and warrants urgent vascular imaging. **Mnemonic: BRUIT = Best Reason for Ultrasound In renal artery Tension** (secondary hypertension)
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