Small Kidneys Chronicity Marker Ultrasound — ESENeph MCQ

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EasyChronic Kidney DiseaseSmall Kidneys Chronicity Marker UltrasoundESENeph

A 45-year-old man is found to have bilateral small kidneys (8 cm each) on ultrasound, eGFR 32 mL/min/1.73m2, and uPCR 45 mg/mmol. He is asymptomatic. There is no family history of kidney disease. Blood tests 5 years ago showed normal creatinine. What does bilateral small kidneys on ultrasound most reliably indicate?

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Correct answer: A — Chronicity of kidney disease

Bilateral small kidneys (<9 cm or <2 standard deviations below mean for height) on ultrasound indicate chronicity and irreversibility — the kidneys have undergone cortical loss, nephron dropout, and fibrotic shrinkage over time. This is a key distinguishing feature between AKI (where kidneys are typically normal-sized or enlarged) and CKD. The finding confirms that kidney damage has been present and progressive for an extended period, even if only recently detected biochemically. It does not indicate a specific aetiology. Exceptions to the 'small kidneys = CKD' rule include diabetic nephropathy, amyloidosis, ADPKD, and HIV-associated nephropathy, where kidneys may remain normal-sized or enlarged despite advanced CKD.

Reference: KDIGO 2024 – CKD Guideline; NICE 2021 – NG203 CKD; O'Neill 2000 – Renal Ultrasound in CKD