AKI on CKD
Formal Definition
Acute kidney injury (AKI) superimposed on underlying chronic kidney disease (CKD), characterized by an acute rise in creatinine (≥0.3 mg/dL within 48 hours or ≥1.5× baseline within 7 days) in a patient with already-reduced kidney function; requires distinguishing acute from chronic changes.
How It's Used on the Ward
"AKI on CKD" — commonly said on rounds as a combined diagnosis; management differs from isolated AKI because baseline function is already impaired.
Example
""Baseline creatinine is 2.4 — she's stage 3B CKD from hypertensive nephrosclerosis. Admitted with Cr 4.1 after two weeks of ibuprofen for knee pain. Classic AKI on CKD: hold NSAIDs, hold ACEi, hydrate carefully, nephrology following.""
Clinical Context
AKI on CKD has higher mortality and worse recovery than either alone — the reduced nephron reserve means less tolerance for further insults. Pre-renal AKI (volume depletion, decreased perfusion) is the most common and most reversible. Intrinsic renal AKI (ATN, interstitial nephritis) requires identifying the offending agent. Post-renal (obstruction) must always be excluded — bladder scan or ultrasound for hydronephrosis. The "creatinine is only 1.4" trap: in an elderly, low-muscle-mass patient, Cr 1.4 may represent <30 mL/min GFR.