Expansion
Prerenal, intrinsic renal and postrenal
Expansion
Prerenal - reduced perfusion, tubules intact
- Hypovolaemia, haemorrhage, sepsis, heart failure, hepatorenal syndrome
- Drugs: ACE inhibitors, angiotensin receptor blockers, NSAIDs, diuretics
- FENa under 1 per cent, concentrated urine, bland sediment
Intrinsic renal
- Tubular: acute tubular necrosis from ischaemia or toxins (aminoglycosides, contrast, myoglobin)
- Glomerular: glomerulonephritis
- Interstitial: acute interstitial nephritis, classically drug-induced with eosinophilia
- Vascular: vasculitis, thrombotic microangiopathy, cholesterol emboli
Postrenal - obstruction
- Stones, prostatic enlargement, malignancy, retroperitoneal fibrosis
- Requires bilateral obstruction, or unilateral in a single functioning kidney
Staging is by the KDIGO criteria, using the rise in creatinine and the urine output.
Prolonged prerenal injury progresses to acute tubular necrosis, so the categories form a continuum rather than distinct entities.