AKI is the scenario most likely to reward a candidate who thinks in systems. The diagnosis is easy; the marks are in a structured cause list, a medication review nobody forgets to mention, and knowing exactly when this stops being your problem alone.

How is AKI defined and staged?

AKI is detected using any of a rise in serum creatinine of 26 micromol/L or more within 48 hours, a 50% or greater rise in creatinine known or presumed to have occurred within the past 7 days, or a fall in urine output to less than 0.5 mL/kg/hour for more than 6 hours. Staging follows KDIGO, from stage 1 to stage 3, on the same two axes of creatinine and urine output.

Say the urine output criterion. Candidates who define AKI on creatinine alone miss the oliguric patient whose creatinine has not moved yet.

How do you structure the causes?

Pre-renal

Hypoperfusion: hypovolaemia, sepsis, cardiac failure, hepatorenal syndrome. The commonest group by far, and the one most often reversible on the ward.

Renal

Acute tubular necrosis, glomerulonephritis, interstitial nephritis, vasculitis, myeloma. This is where you mention a urine dipstick — blood and protein change the whole pathway and should prompt an urgent renal opinion.

Post-renal

Obstruction. Say you would examine for a palpable bladder and request an ultrasound of the urinary tract, because this is the cause you can fix with a catheter in five minutes.

What is the immediate management?

  • Assess and correct volume status, reassessing after each fluid challenge rather than prescribing a fixed regimen
  • Review every drug: stop nephrotoxics such as NSAIDs, ACE inhibitors, ARBs and aminoglycosides, and dose-adjust those that are renally cleared
  • Treat sepsis and relieve obstruction
  • Monitor potassium and treat hyperkalaemia — an ECG belongs in your answer, not just a blood test

When do you call the renal team?

Have the indications for urgent renal replacement therapy ready as a list, because this is the closed question the panel uses to separate the top scores.

  • Hyperkalaemia refractory to medical management
  • Metabolic acidosis refractory to medical management
  • Fluid overload refractory to medical management, particularly pulmonary oedema
  • Uraemic complications — pericarditis or encephalopathy

Also refer early, ahead of those, if the cause is unclear, there is suspicion of intrinsic renal disease, or the AKI is not responding to treatment. Add the caveat NICE makes explicitly: the decision to start renal replacement therapy rests on the condition of the patient as a whole, not on an isolated urea, creatinine or potassium value.