MRCP(UK) Part 1 common mistakes
MRCP(UK) Part 1 · Understand the traps and how to avoid them.
Judging the severity of aortic stenosis from how loud the systolic murmur is, so a loud murmur is labelled severe and a quiet one is called mild.
Loudness feels like a natural proxy for severity, and candidates rehearse the murmur's location and radiation but not the bedside signs that actually grade stenosis. Loudness reflects flow and chest-wall transmission, not valve area, and a low-flow failing ventricle can make severe stenosis sound quiet.
What to do instead
Grade stenosis with the whole picture: a soft or absent aortic component of the second heart sound, a slow-rising low-volume pulse, a narrow pulse pressure, a late-peaking murmur and a long ejection time all point to severe disease. Whenever you see a murmur option set, explicitly look for the S2, pulse character and pulse pressure in the stem before choosing.
In suspected pulmonary embolism, choosing CT pulmonary angiography as the next step for a patient who is already hypotensive or in shock.
Candidates over-learn 'CTPA is the gold standard' and answer the diagnostic question that would apply to a stable patient, ignoring the haemodynamic details given at the start of the stem.
What to do instead
Triage PE stems by stability before choosing any test. With sustained hypotension or shock and no contraindication, the answer is reperfusion (thrombolysis, or embolectomy if thrombolysis is contraindicated); bedside echocardiography can support the decision but should not delay treatment. Reserve CTPA (or V/Q if renal impairment/contrast allergy) for haemodynamically stable patients.
Matching autoimmune liver disease to the wrong autoantibody, for example selecting anti-mitochondrial antibody for primary sclerosing cholangitis or anti-smooth-muscle antibody for primary biliary cholangitis.
These four antibodies are learned as a list in one revision session and then blur together; exam stems often give the antibody in the stem rather than asking for it, which rewards precise recall over pattern-matching the clinical vignette.
What to do instead
Anchor each antibody to a one-line anchor: AMA (M2) = PBC, middle-aged woman, itch, raised ALP; anti-smooth muscle/ANA = AIH type 1; anti-LKM1 = AIH type 2; p-ANCA = PSC, young man with ulcerative colitis. Test yourself by going from antibody to disease as well as disease to antibody.
Diagnosing hypothyroidism (or hyperthyroidism) in an inpatient from a single set of thyroid function tests showing a low free T4 with a normal or low TSH.
Candidates apply the outpatient algorithm rigidly and forget that acute illness, drugs and assay interference all suppress the axis; they also conflate 'low T4' with 'primary hypothyroidism'.
What to do instead
In a non-thyroidal illness pattern (low or normal TSH with low free T4), do not treat; repeat in 4-6 weeks once the patient has recovered. Consider drug causes (amiodarone, glucocorticoids, dopamine) and biotin assay interference. Treat only when the TSH is clearly and persistently elevated with a low free T4, and remember that a raised TSH alone in a recovering inpatient may be transient.
Calculating the anion gap as sodium minus chloride minus bicarbonate and interpreting it against the normal range without correcting for albumin, and sometimes including potassium in the sum.
Textbook formulas get memorised in one form, and the albumin correction is a small extra step that is easy to drop under time pressure; many candidates also never learned that hypoalbuminaemia masks a raised gap.
What to do instead
Use Na+ minus (Cl- + HCO3-), never include K+, and add 2.5 mmol/L to the calculated gap for every 10 g/L the albumin is below 40 g/L. If the gap is raised, calculate the delta ratio to detect a mixed high- and normal-gap acidosis; if the gap looks normal but albumin is low, recalculate before excluding a high-gap cause.
Labelling a third nerve palsy as benign or microvascular when the stem describes a dilated, unreactive pupil, or conversely pursuing urgent angiography for a pupil-sparing palsy in a patient with diabetes.
Candidates learn 'diabetic third nerve palsy spares the pupil' as a fact but do not use pupillary involvement as the discriminating feature when it is the decisive detail in the stem.
What to do instead
Treat pupil involvement as the localising sign: a painful pupil-involving third nerve palsy suggests compression, classically a posterior communicating artery aneurysm, and needs urgent neuroimaging with vascular imaging. Pupil-sparing palsy with an ipsilateral-sparing pattern in a patient with vascular risk factors is usually ischaemic and can be observed with close follow-up. Always state which feature drove your choice.
Pairing a connective tissue disease with the wrong autoantibody, for example linking anti-centromere with diffuse systemic sclerosis or anti-Jo-1 with systemic lupus erythematosus.
Antibody lists are memorised late in revision and the names are visually similar; stems often present the clinical phenotype and ask for the antibody, so an imprecise association loses the mark even when the diagnosis is right.
What to do instead
Learn antibody to disease and disease to antibody in both directions with a fixed anchor: anti-centromere = limited cutaneous SSc/CREST; anti-topoisomerase (Scl-70) = diffuse SSc with lung fibrosis; anti-RNA polymerase III = diffuse SSc with renal crisis; anti-Jo-1 = antisynthetase syndrome (myositis, ILD, mechanic's hands); anti-U1RNP = mixed connective tissue disease; anti-Ro = Sjögren and neonatal lupus; anti-Smith = SLE-specific.
Prescribing a platelet transfusion for thrombocytopenia in a patient with microangiopathic haemolytic anaemia and suspected TTP.
The reflex 'low platelets mean give platelets' response overrides the specific contraindication, and the blood film findings (schistocytes) are noted but not linked to the management decision.
What to do instead
When you see thrombocytopenia with anaemia and schistocytes, fragment red cells and a normal coagulation screen, diagnose a thrombotic microangiopathy and treat as a haematological emergency: urgent plasma exchange and steroids, with ADAMTS13 sent before treatment. Platelet transfusion is contraindicated unless there is life-threatening bleeding, as it can worsen thrombosis.
Investigating a febrile returning traveller from sub-Saharan Africa with dengue or typhoid serology first, or excluding malaria after a single negative blood film.
Candidates reach for the 'exotic' test or accept one negative result as exclusion, not appreciating that a single thick film has limited sensitivity and that malaria is the diagnosis that must be excluded first because it kills quickly.
What to do instead
For any fever in a returning traveller, send thick and thin films immediately; if the first set is negative and suspicion remains, repeat films at 12-24 hour intervals for up to three sets. Use rapid antigen tests as an adjunct, not a substitute in high suspicion. Only after malaria is being excluded should you focus on dengue, typhoid, rickettsia or viral haemorrhagic fever according to exposure and incubation period.
Predicting that the serum phenytoin level will rise in direct proportion to a dose increase, or using the standard 'four to five half-lives to steady state' rule for phenytoin.
First-order kinetics are taught as the default and candidates apply the half-life rule universally, without recalling which drugs saturate hepatic metabolism.
What to do instead
Keep a short list of drugs showing zero-order (saturable) kinetics at therapeutic or toxic doses: phenytoin, ethanol, salicylates at high dose, and theophylline at high concentration. For these, small dose increments can cause disproportionate and toxic level rises, so increase cautiously, measure levels, and do not apply a fixed half-life to predict time to steady state.