Iran Specialty Board - Internal Medicine common mistakes
Iran Specialty Board - Internal Medicine · Understand the traps and how to avoid them.
When a vignette gives an ABG with a low pH, low HCO3 and low PaCO2, the candidate labels the disorder 'metabolic acidosis' and stops, ignoring the superimposed respiratory alkalosis or the calculated anion gap and delta-delta.
Training emphasizes naming the primary disorder; candidates rarely practise the three-step framework (pH vs PaCO2 direction, anion gap, delta ratio) under time pressure, so the second and third steps get skipped even when the numbers are supplied.
What to do instead
Build a fixed written template for every acid-base item: (1) pH direction, (2) primary respiratory vs metabolic by comparing change in PaCO2 with change in HCO3, (3) anion gap = Na − (Cl + HCO3), (4) delta ratio = ΔAG / ΔHCO3 to detect a second metabolic process, (5) Winter's formula (expected PaCO2 = 1.5 × HCO3 + 8 ± 2) for metabolic acidosis. Practise 20 ABG vignettes applying all five steps in under 90 seconds each.
The candidate treats a high-sensitivity troponin as diagnostic of acute myocardial infarction without checking whether it is rising/falling, whether the patient has a compatible ischaemic history, or whether a better explanation exists (pulmonary embolism, sepsis, heart failure, renal failure).
Troponin is mentally filed as 'the heart attack test'; exam writers exploit this by giving a mildly elevated troponin in a non-ischaemic scenario, and candidates anchor on the number rather than the Fourth Universal Definition criteria.
What to do instead
Recite the definition before answering: myocardial injury = elevated troponin above the 99th percentile; acute MI additionally requires a rise and/or fall plus evidence of ischaemia (symptoms, ECG changes, imaging). For every elevated troponin item, explicitly write down 'injury vs infarction' and 'rise/fall present or not' before choosing the answer.
Faced with a hyponatraemic patient, the candidate computes the sodium deficit and starts hypertonic saline without first classifying by volume status and urine osmolality/urine sodium, and without checking for hypothyroidism, adrenal insufficiency or thiazide use.
The arithmetic is satisfying and feels like 'doing the treatment', so the diagnostic classification step gets compressed; candidates also forget that SIADH requires euvolaemia and exclusion of other causes.
What to do instead
Use a mandatory decision tree: serum osmolality (exclude pseudohyponatraemia and hyperglycaemia) → volume status on examination → urine osmolality (<100 suggests primary polydipsia; >100 suggests ADH effect) → urine sodium → review drugs (thiazides, SSRIs, carbamazepine) and screen for hypothyroidism/adrenal insufficiency. Reserve 3% saline for symptomatic or severe cases with a documented 4–6 mmol/L rise target and correction limit of 8–10 mmol/L per 24 hours.
In a patient with a painful, swollen leg or a patient with pleuritic chest pain and hypoxia, the candidate orders D-dimer and uses a negative or positive result as if it were diagnostic, without applying the Wells score or checking whether the patient is D-dimer-eligible.
D-dimer is memorised as 'the rule-out test'; the concept that it is only valid in low/intermediate pre-test probability and is uninterpretable in hospitalised, pregnant, elderly or post-surgical patients is under-rehearsed.
What to do instead
For every dyspnoea or leg-swelling vignette, first assign a Wells score in writing. Only if low/intermediate probability, order a D-dimer (age-adjusted cutoff above 50 years). If high probability, go directly to CT pulmonary angiography or compression ultrasound. Practise recognising the traps: recent surgery, malignancy, pregnancy, immobilisation, and already-hospitalised patients.
The candidate reads a creatinine and calls the renal function 'normal' without adjusting for age, sex and weight, and without noticing that a 'normal' creatinine in an elderly, low-muscle-mass patient can mask a substantially reduced estimated GFR.
Reference ranges on the lab report are population-based, not individualised; candidates anchor on the bold 'normal' flag and skip the eGFR calculation and the trend.
What to do instead
Always compute eGFR (CKD-EPI) and compare with previous values to detect a rise. For drug dosing and AKI staging, use the KDIGO urine-output and creatinine criteria explicitly. Remember that a creatinine rise of 0.3 mg/dL in 48 hours already meets AKI stage 1, and that cystatin C or measured clearance may be needed in extremes of muscle mass.
When a diabetic patient presents with malaise, the candidate checks glucose and ketones only, missing the anion-gap calculation, the potassium level before insulin, and the distinction between diabetic ketoacidosis and hyperosmolar hyperglycaemic state.
DKA is taught as 'high glucose, ketones, acidosis', so candidates stop at the first two and forget that the diagnostic triad requires the anion gap and bicarbonate, and that potassium must be checked before insulin is started.
What to do instead
For every hyperglycaemic emergency, record: glucose, blood ketones, venous pH, bicarbonate, anion gap, calculated effective osmolality (2 × Na + glucose/18), and potassium. State the diagnosis with criteria. State the potassium rule: if K <3.3 mmol/L, give potassium before insulin; if 3.3–5.2, give insulin with potassium replacement; if >5.2, hold potassium and recheck.
The candidate selects a treatment for a condition without checking the patient's renal and hepatic function, pregnancy status, or interacting medications listed in the stem, and without recognising when the correct answer is dose reduction or avoidance rather than the drug itself.
Pharmacology is recalled as 'drug X treats disease Y'; the vignette details about eGFR, cirrhosis, gestation and co-prescriptions are read as background rather than as the decisive constraint.
What to do instead
Before choosing any drug, scan the stem for four filters: renal function, hepatic function, pregnancy/lactation, and interacting drugs (e.g. CYP inhibitors, warfarin, statins, QT-prolonging agents). Learn the common contraindication pairs: metformin and severe renal impairment, NSAIDs and CKD/heart failure, ACE inhibitors in pregnancy, fluoroquinolones with QT prolongation, and nitrates with phosphodiesterase-5 inhibitors.
In a febrile or septic patient, the candidate chooses an antibiotic without addressing source control, without taking cultures before antibiotics, and without recognising that the stem describes a presentation needing drainage or surgery rather than another drug.
The question format pushes toward a single drug choice; source control and culture timing are cognitive steps that do not map onto the answer options, so they are skipped.
What to do instead
For every infection vignette, answer three questions in writing before reading the options: (1) what is the source, (2) does it need drainage, debridement or device removal, (3) what cultures are needed and when. Then match empirical therapy to the likely organism, local resistance patterns and severity. Recognise classic source-control scenarios: abscess, empyema, obstructed pyelonephritis, cholangitis, infected prosthetic material, and necrotising fasciitis.
The candidate interprets a peripheral blood smear or a coagulation panel in isolation, missing that a normal platelet count with prolonged aPTT and a history of bleeding after dental work suggests a factor deficiency, or that schistocytes plus thrombocytopenia plus renal failure suggests thrombotic microangiopathy.
Haematology is memorised as lists of diseases rather than as pattern recognition from a small number of laboratory variables; candidates do not rehearse the classic combinations.
What to do instead
Learn the high-yield patterns as fixed triads: prolonged aPTT with normal PT and normal platelets → factor VIII/IX/XI deficiency or lupus anticoagulant; prolonged PT and aPTT with low platelets and low fibrinogen → DIC; MAHA with thrombocytopenia and renal injury → TTP/HUS; pancytopenia with a hypocellular marrow → aplastic anaemia. For each, write the confirmatory test (mixing study, ADAMTS13, schistocyte count, bone marrow biopsy).
When a patient presents with acute confusion or a fall, the candidate jumps to a primary neurological or psychiatric diagnosis without systematically excluding delirium, medication effects, infection, metabolic disturbance and pain, and without reviewing the full medication list.
Geriatric presentations are atypical and the stem often provides a single dramatic detail (a head CT, a low sodium, a new drug) that pulls attention away from the multifactorial assessment; candidates under-use the delirium and falls frameworks.
What to do instead
For any older patient with acute change, apply a fixed checklist: baseline cognition and function, medication review (anticholinergics, sedatives, opioids, hypoglycaemics, antihypertensives), infection screen, electrolytes and glucose, pain, constipation and urinary retention, sensory deficit, and environment. Use the 4AT or CAM for delirium, and a structured falls review covering orthostatic blood pressure, vision, gait, footwear, home hazards and bone health.