PLAB Part 1 (UKMLA applied knowledge test)

A 76 year old man has been vomiting for three days with poor oral intake. His creatinine is 240 micromol/L against a baseline of 88. He is clinically dehydrated with dry mucous membranes, a pulse of 104 beats/minute and a postural drop of 25 mmHg. His bladder scan shows 30 mL. Urine dipstick is negative for blood and protein. What is the SINGLE most likely diagnosis?

1. Acute kidney injury A rise in creatinine of 26 micromol/L in 48 hours, or 1.5 times baseline in seven days, or urine output under 0.5 mL/kg/h for six hours. A postural drop with an empty bladder and a clean dipstick fits.
2. Acute tubular necrosis Follows sustained hypoperfusion or nephrotoxins, with muddy brown casts and a urine sodium above 40 mmol/L. A postural drop with an empty bladder and a clean dipstick makes it worth distinguishing.
3. Pre-renal azotaemia correct Correct. Vomiting, dry membranes, tachycardia and a 25 mmHg postural drop is volume depletion. The empty bladder excludes obstruction and the clean dipstick argues against intrinsic renal disease, which leaves hypoperfusion, the commonest cause of AKI by a wide margin.
4. Glomerulonephritis Red cell casts and proteinuria with hypertension. A postural drop with an empty bladder and a clean dipstick does not show that.
5. Chronic kidney disease A long-standing raised creatinine with small kidneys, anaemia and renal bone disease. A postural drop with an empty bladder and a clean dipstick shows an acute change instead.

The point: Classify by site: pre-renal (hypoperfusion, the commonest), renal (intrinsic damage) or post-renal (obstruction). Every AKI gets a bladder scan and a urine dipstick. Obstruction is the cause you can reverse in minutes. Stop the DAMN drugs: Diuretics, ACE inhibitors and ARBs, Metformin, NSAIDs. Dialyse for refractory hyperkalaemia, acidosis, fluid overload, uraemic complications or poisoning.

Source: NICE NG148 — Acute kidney injury: prevention, detection and management NICE · tier 1, national regulator or guidance

A 76 year old man has been vomiting for three days with poor oral intake. His creatinine is 240 micromol/L against a baseline of 88. He is clinically dehydrated with dry mucous membranes, a pulse of 104 beats/minute and a postural drop of 25 mmHg. His bladder scan shows 30 mL. Urine dipstick is negative for blood and protein. What is the SINGLE most appropriate initial investigation?

1. Serum creatine kinase For suspected rhabdomyolysis after a long lie, crush injury or seizure. A postural drop with an empty bladder and a clean dipstick raises that.
2. Renal ultrasound For suspected obstruction where the bladder scan is unhelpful, or when no cause is apparent within 24 hours. A postural drop with an empty bladder and a clean dipstick indicates it.
3. Urine dipstick Blood and protein point to intrinsic renal disease and change the referral pathway entirely. A postural drop with an empty bladder and a clean dipstick makes it essential.
4. Bladder scan correct Correct. Done in every AKI, because obstruction is the one cause reversible in minutes and a distended bladder changes the management completely. Thirty millilitres rules it out here in under a minute.
5. Venous blood gas Gives potassium and pH within minutes, which is what decides whether this is an emergency. A postural drop with an empty bladder and a clean dipstick makes speed the point.

The point: Classify by site: pre-renal (hypoperfusion, the commonest), renal (intrinsic damage) or post-renal (obstruction). Every AKI gets a bladder scan and a urine dipstick. Obstruction is the cause you can reverse in minutes. Stop the DAMN drugs: Diuretics, ACE inhibitors and ARBs, Metformin, NSAIDs. Dialyse for refractory hyperkalaemia, acidosis, fluid overload, uraemic complications or poisoning.

Source: NICE NG148 — Acute kidney injury: prevention, detection and management NICE · tier 1, national regulator or guidance