Examqo › Examqo library › Internal medicine › Nephrology and electrolytes · IMLE
Acute kidney injury (AKI)
AKI is defined by a rise in creatinine or a fall in urine output (KDIGO), and every case is placed in one of three groups — prerenal, intrinsic (mainly ATN) and postrenal — because each group is treated differently.
Why it matters in the exam
AKI questions start with an inpatient whose creatinine has risen and ask the candidate to separate the causes. The KDIGO definition must be remembered (creatinine up by at least 0.3 mg/dL in 48 hours, or to 1.5 times its baseline over 7 days, or urine output under 0.5 mL/kg per hour for 6 hours) along with the stages of severity. Then come the urine indices: FENa below 1% points to a prerenal cause and above 2% to ATN, and in a patient on diuretics FEUrea is used (below 35% = prerenal). On urinalysis: muddy brown granular casts — ATN; red cell casts — glomerulonephritis; white cell casts with rash and fever after a drug — acute interstitial nephritis.
Another important theme is the indications for urgent dialysis: severe acidosis that does not respond, refractory hyperkalaemia, fluid overload with pulmonary oedema not responding to diuretics, poisonings that dialysis can clear (salicylates, lithium, toxic alcohols such as methanol) and complications of uraemia — a pericardial rub, confusion or bleeding. Case questions also deal with rhabdomyolysis (high CK, a urine dipstick positive for blood without red cells on microscopy — large volumes of fluid), contrast-associated injury and drugs to stop (NSAIDs, ACEi, ARB, diuretics, metformin). A postrenal cause is found on ultrasound as hydronephrosis, and in an older man the first step is a catheter.
Key points
- KDIGO: creatinine up by 0.3 mg/dL in 48 hours, or to 1.5 times baseline in 7 days, or urine below 0.5 mL/kg per hour for 6 hours.
- FENa below 1% prerenal; above 2% ATN; on diuretics FEUrea below 35%.
- Casts: granular = ATN, RBC = glomerulonephritis, WBC = interstitial nephritis.
- Always an ultrasound to exclude obstruction.
- Urgent dialysis: acidosis, hyperkalaemia, fluid overload, poisoning, uraemia — when they do not respond to treatment.
Summary table
| Type | Indices | Urine and clinical clue | Treatment |
|---|---|---|---|
| Prerenal | FENa below 1%, FEUrea below 35%, urine sodium below 20 | "Bland" urine, BUN/creatinine above 20 | Fluids, stop NSAIDs and ACEi |
| ATN | FENa above 2%, urine osmolality below 350 | Muddy brown granular casts | Supportive care, fluid balance, avoid nephrotoxins |
| Acute interstitial nephritis | A drug (beta-lactam, PPI, NSAIDs) | White cell casts, rash, fever, eosinophilia | Stop the drug ± steroids |
| Glomerulonephritis | Protein and blood in the urine | Red cell casts, hypertension, oedema | Serology, biopsy, treat the cause |
| Postrenal | Hydronephrosis on ultrasound | Urinary retention, enlarged prostate, pelvic tumour | Catheter or drainage |
| AKI stage 3 | Creatinine 3 times baseline, or 4.0 mg/dL or more, or need for dialysis | Urine below 0.3 mL/kg per hour for 24 hours | Consider dialysis by indications |
Free exam questions
איזה מ בין הצמדים הבאים מתאר הכי מדויק את הקשר בין נפרוטוקסין למקום פגיעתו המדויק ב כליה ? (the question as examined, in Hebrew)
- א. myoglobin - glomeruli
- ב. iodinated contrast - renal papillae
- ג. gentamycin - vasa recta
- ד. hemoglobin - tubules
A 24-year-old male, several incidents of urinary tract infections during his childhood without other pre-existing medical conditions. In a random blood test, a finding of creatinine 1.6, the other laboratory tests are normal. Renal US: small kidneys bilaterally, thin cortex and areas of compensatory hypertrophy. Urine test: protein+, no red or white blood cells. What is the most likely diagnosis?
- A. Allergic Interstitial Nephritis
- B. IgG4 Related Disease
- C. Reflux Nephropathy
- D. Sjögren's syndrome
In the full version for subscribers
- A simple algorithm
- Memory aid
- Exam traps
- 5 review cards
- Enough for IMLE
The full version is open to subscribers of: Medical licensing exam (IMLE), Internal medicine, Emergency medicine, Geriatrics, Anesthesiology, Occupational medicine, Pediatric surgery, Pediatrics, Diagnostic radiology, General surgery, Cardiothoracic surgery, Urology.
Subscriber? Read the full topic Plans and prices 25 free questions
Sources
- KDIGO Clinical Practice Guideline for Acute Kidney Injury, 2012 — Definition, staging and management of AKI
- Harrison's Principles of Internal Medicine, 21st edition (2022) — Acute Kidney Injury
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.