Creatinine doubles after dehydration — prerenal AKI; fluids restore kidney function. AKI (sudden — prerenal: dehydration, hypotension — fluids; renal: ATN — nephrotoxins, sepsis; postrenal: obstruction — prostate, stones — relieve): creatinine rise, oliguria; treat cause, stop nephrotoxins (NSAIDs, aminoglycosides), monitor K+/acidosis. CKD (>3 months — eGFR <60: diabetes/hypertension commonest: fatigue, anemia, bone disease; stages 1–5): BP control, ACE-I/ARB, SGLT2i, anemia (iron/EPO), calcium/vitamin D; prepare — fistula, transplant workup. Dialysis (AEIOU — refractory acidosis, hyperkalemia, intoxication, overload, uremia). The creatinine trend is the story — sudden is AKI, slow is CKD.