Nephrology
Acute kidney injury
Written 30 September 2026.
Why this matters
A rising creatinine is a description. The useful question is pre-renal, intrinsic, or obstruction.
Rapid clinical summary
- Obstruction, including a blocked bladder, is the cause you must not miss.
- Life threats are potassium, acid, volume, and pulmonary edema.
- A drug list often explains more than a rare biopsy diagnosis.
Mechanism
Filtration falls because perfusion falls, the kidney itself is injured, or urine cannot leave. Creatinine rises after the fact. Urine output can fall before the number does.
Recognition
Examine the abdomen and the bladder before you call it tubular necrosis.
Typical
- Oliguria
- A recent illness or operation
- New drugs
- A palpable bladder
Red flags
- Anuria
- Pulmonary edema
- Hyperkalemia
- Acidosis
- A palpable bladder
Differential
| Condition | Clue | Trap |
|---|---|---|
| Pre-renal | Losses, low intake, shock, a drug that drops filtration | Fluids in a patient who is already overloaded |
| Intrinsic | A toxic drug, vasculitis, a long period of shock | Missing obstruction first because intrinsic sounds more complex |
| Post-renal | Anuria, a mass, pelvic disease, a catheter that is blocked | A normal ultrasound ordered tomorrow instead of relieving the bladder today |
Investigations
- Creatinine trend, potassium, and acid-base.
- Bladder scan or catheterization when retention is possible.
- Ultrasound if obstruction above the bladder is still possible.
Management
- Immediate
- Relieve obstruction if it is there. Treat hyperkalemia and pulmonary edema as their own emergencies.
- Definitive
- Restore perfusion if the patient is volume-depleted. Stop the nephrotoxin. Do not fluid-load pulmonary edema. Doses and fluid volumes are not stated.
- Monitoring
- Urine output, potassium, and volume status. A catheter that drains nothing may be blocked or misplaced.
Common pitfalls
- Labeling a palpable bladder as ‘acute tubular necrosis’.
- Giving a fluid bolus to obvious pulmonary edema.
- Ignoring an ACE inhibitor plus a dehydrating illness.
Exam reasoning
The best answer is often the missed obstruction, or the life threat, not the rarest glomerular disease.
Practice this topicOpens original Mahazanaka questions in this subject. If this subject is thin on that track, the session uses what exists.
Visual summary
Obstruction before a rare label.
Recognize, reason, prioritize, act safely
- Recognize. Creatinine or urine output has changed.
- Reason. Pre-renal, renal, or post-renal?
- Prioritize. Potassium, acid, volume, obstruction.
- Act safely. Relieve what you can relieve today.
Knowledge check
Almost no urine, a dull lower-abdominal mass, prior pelvic surgery. What must be excluded first?
No citation is attached to this chapter. Nothing here is personal medical advice.