Acute Kidney Injury

Topics: Categorizing acute kidney injury, Approach to acute kidney injury, Acute kidney injury requiring dialysis.

Categorizing Acute Kidney Injury

Acute kidney injury can be categorized into 3 main groups: pre-renal, renal and post-renal. Any problems with the heart, or blood supply reaching the kidneys is considered pre-renal. Any problems inside the kidney itself is considered intra-renal. Any problems occurring with urine being able to leave the kidneys i.e. in the ureters, bladder, urethra is post-renal. Post-renal AKI is kidney damage due to back up of urine produced by the kidneys into the kidney itself. Pre-renal AKI is kidney damage due to a lack of blood flow to the kidneys. Intra-renal AKI can be divided into 3 main categories: problems with the glomerulus (mainly glomerulonephritis), problems with the renal interstitium (acute interstitial nephritis) or problems with the renal tubules (acute tubular necrosis).

Heart attack or heart failureGlomerulonephritisUreter cancer or stones
leaky vasculature (low albumin): nephrosis, gastrosis (protein losing enteropathies/ malnutrition), cirrhosis. Volume-overloaded. Acute interstitial nephritisBladder cancer/ stones, or neurogenic bladder
Bleeding: diuresis, diarrhea, dehydration, hemorrhage. Hypovolemic. Acute tubular necrosisUrethral cancer/ stones, or benign prostatic hyperplasia, or foley catheter
Blood flow is blocked: fibromuscular dysplasia, renal artery stenosis

Approach to Acute Kidney Injury

An elevated creatinine suggests acute kidney injury. First, asses if it is pre-renal AKI and next if it is post-renal AKI and then finally check if it is intra-renal AKI.

Pre-renal AKI: BUN/Cr (>20), UNa (<10), FeNa (<1%) or if on a diuretic the FeUrea (<35%). Check volume status, if hypovolemic give IV fluids, but if volume overloaded then diuresis is done.

Post-renal AKI: Ultrasound or CT scan shows hydroureter or hydronephrosis. CT scan can identify stones causing the obstruction. Treatment involves removing the obstruction. If the obstruction is in the urethra or bladder a foley catheter is used. If the obstruction is at the ureter then nephrostomy or surgery.

Intra-renal AKI: First a thorough history and physical exam followed by urinalysis. Often this is enough to arrive at the diagnosis but if not you may need a biopsy. Treatment is disease specific. Examples of intra-renal AKI include diabetic nephropathy and hypertensive nephropathy.

Acute kidney injury requiring Dialysis


Acidosis, Electrolytes (K, Ca), Intoxication, Overload, Uremia.