Q1. Which urinary finding is characteristic of acute tubular necrosis? A. Red cell casts B. Muddy brown granular casts C. Bland sediment with low urinary sodium D. White cell casts only ANSWER: B — muddy brown granular casts. Why: sloughed tubular epithelial cells form these casts in ATN. A: red cell casts indicate glomerulonephritis. C: describes pre-renal azotaemia. LEARNING POINT: the urine sediment separates the intrinsic causes from the pre-renal ones.

Q2. In hyperkalaemia, intravenous calcium gluconate acts by: A. Lowering serum potassium rapidly B. Stabilising the cardiac membrane without lowering potassium C. Increasing renal potassium excretion D. Shifting potassium into cells ANSWER: B — membrane stabilisation. Why: calcium antagonises the effect of potassium on the myocardium, protecting against arrhythmia. It does not alter the potassium level at all. D: that is insulin with glucose, or salbutamol. LEARNING POINT: stabilise, shift, remove — three separate jobs, three separate drugs.

Q3. An 82-year-old on ramipril and furosemide develops gastroenteritis and takes ibuprofen. Creatinine rises from 90 to 300. The mechanism is: A. Direct nephrotoxicity of ibuprofen alone B. Loss of both afferent dilation and efferent constriction during hypovolaemia C. Obstruction D. Glomerulonephritis ANSWER: B. Why: the NSAID blocks prostaglandin-mediated afferent dilation, the ACE inhibitor blocks angiotensin-mediated efferent constriction, and the diuretic plus diarrhoea depletes volume. All three renal defences are disabled at once. LEARNING POINT: none of these drugs is wrong alone. The combination during dehydration is the problem.

Q4. An anuric patient with K⁺ 7.2 receives calcium and insulin–dextrose; potassium falls to 5.5. The next step is: A. No further action — the problem is treated B. Arrange definitive removal (dialysis or a binder) C. Give further insulin only D. Start a loop diuretic ANSWER: B — arrange removal. Why: insulin shifts potassium into cells but removes none from the body. In an anuric patient there is no excretory route, so it will rise again. D: diuretics are ineffective in an anuric patient. LEARNING POINT: shifting buys time; it does not solve the problem.

Q5. A 78-year-old with a poor urinary stream has creatinine 460 and a distended, dull suprapubic abdomen. The most appropriate immediate action is: A. Fluid challenge B. Bladder scan and urethral catheterisation C. Urgent dialysis D. Renal biopsy ANSWER: B — bladder scan and catheterise. Why: this is post-renal AKI from retention. Relieving the obstruction is immediate, cheap and definitive, and every hour of delay costs nephrons. A: could worsen an already overloaded patient. LEARNING POINT: exclude obstruction EARLY, and anticipate post-obstructive diuresis afterwards.

Q6. A patient with proteinuric CKD starts an ACE inhibitor. Creatinine rises from 145 to 162 at two weeks, potassium 4.8, blood pressure improved. The correct action is: A. Stop the ACE inhibitor immediately B. Continue and recheck — a small rise is expected C. Halve the dose and add an NSAID D. Refer for urgent dialysis ANSWER: B — continue and recheck. Why: ACE inhibitors reduce intraglomerular pressure by dilating the efferent arteriole. That produces a small, expected creatinine rise and IS the mechanism of long-term renal protection. A: discards the benefit for an anticipated effect. A large or progressive rise would be different, and raises the question of renal artery stenosis. LEARNING POINT: distinguish the intended effect from a warning sign.

Q7. A frail 84-year-old woman weighing 42 kg has a creatinine of 96 µmol/L. This most likely indicates: A. Entirely normal renal function B. Possibly significant impairment, because creatinine depends on muscle mass C. Acute kidney injury D. Laboratory error ANSWER: B. Why: creatinine is generated from muscle. In a small, sarcopenic patient, a value within the reference range can correspond to substantially reduced filtration. A: the assumption this question targets. LEARNING POINT: interpret creatinine against the patient in front of you, and use eGFR with the same caution.