NBME CBSSA cheat sheet

Autosomal dominant: vertical transmission, male-to-male possible, 50% recurrence risk per child; examples include Marfan, Huntington, familial hypercholesterolemia, neurofibromatosis type 1.

Autosomal recessive: horizontal pattern, 25% recurrence risk, consanguinity a risk factor; carrier frequency 2√q by Hardy-Weinberg; examples include cystic fibrosis, sickle cell, PKU, Tay-Sachs.

X-linked recessive: no male-to-male transmission, all daughters of affected males are carriers, sons of carrier mothers have 50% risk; examples include hemophilia A/B, Duchenne, G6PD deficiency.

Hardy-Weinberg: p + q = 1 and p² + 2pq + q² = 1; for X-linked traits, affected males = q and carrier females = 2pq.

Rate-limiting enzymes: glycolysis phosphofructokinase-1; gluconeogenesis fructose-1,6-bisphosphatase; TCA isocitrate dehydrogenase; urea cycle carbamoyl phosphate synthetase I; heme synthesis ALA synthase.

Michaelis-Menten: V = Vmax[S]/(Km+[S]); Km is the substrate concentration at half Vmax; competitive inhibitors raise Km with unchanged Vmax; noncompetitive inhibitors lower Vmax with unchanged Km.

Oxygen-hemoglobin dissociation curve right shift (decreased affinity) with increased 2,3-BPG, CO2, H+, temperature; left shift with fetal hemoglobin, CO, methemoglobin, decreased 2,3-BPG.

Virulence and toxin pairs: diphtheria and Pseudomonas exotoxin A inhibit EF-2; cholera toxin and E. coli LT increase cAMP; pertussis toxin increases cAMP via Gi ADP-ribosylation; anthrax toxin has edema and lethal factors.

Gram stain and morphology anchors: lancet-shaped gram-positive diplococci = Streptococcus pneumoniae; gram-negative diplococci = Neisseria; spore-forming gram-positive bacilli = Bacillus or Clostridium; acid-fast = Mycobacteria.

Acute coronary syndrome: ST-elevation STEMI gets emergent reperfusion (PCI within 90 minutes of first medical contact); NSTEMI/unstable angina get aspirin, P2Y12 inhibitor, anticoagulation, and risk-stratified catheterization.

Heart failure with reduced ejection fraction mortality benefit: beta-blocker, ACE inhibitor/ARB/ARNI, mineralocorticoid receptor antagonist, SGLT2 inhibitor; loop diuretics relieve congestion without mortality benefit.

Acute ischemic stroke: noncontrast head CT excludes hemorrhage; IV alteplase within 4.5 hours of last known well; endovascular thrombectomy up to 24 hours in selected large-vessel occlusion.

Diabetic ketoacidosis: IV fluids first, then insulin infusion after potassium is confirmed above 3.3 mEq/L; add dextrose when glucose falls below 200-250 mg/dL; total body potassium is depleted despite normal serum values.

Community-acquired pneumonia: CURB-65 (confusion, urea >7 mmol/L, respiratory rate ≥30, blood pressure low, age ≥65) guides site of care; outpatient without comorbidity gets macrolide or doxycycline.

Hypertension in pregnancy: preeclampsia with severe features or eclampsia gets IV magnesium sulfate for seizure prophylaxis plus antihypertensives (labetalol, hydralazine, nifedipine); delivery is definitive.

Pediatric milestones: social smile 6 weeks, head control 3 months, sits unsupported 6-8 months, walks 12-15 months, two-word phrases 18-24 months, three-word sentences by 3 years.

Screening intervals: colorectal cancer colonoscopy every 10 years from age 45; breast mammography every 1-2 years from 40-50; cervical cytology every 3 years from 21 or co-testing every 5 years from 30.

Thyroid function interpretation: primary hypothyroidism shows high TSH with low free T4; subclinical hypothyroidism shows high TSH with normal free T4; central hypothyroidism shows low free T4 with low or inappropriately normal TSH.

Drug of choice anchors: vancomycin for MRSA; ceftriaxone for gonorrhea and bacterial meningitis in adults; doxycycline for chlamydia and Rocky Mountain spotted fever; metronidazole for bacterial vaginosis and C. difficile first episode.

Prophylaxis timing: preoperative antibiotics within 60 minutes of incision (vancomycin and fluoroquinolones within 120 minutes); discontinue within 24 hours for most procedures.

Venous thromboembolism prophylaxis: low-molecular-weight heparin or fondaparinux for major orthopedic and abdominal surgery; mechanical prophylaxis when bleeding risk is high.

Sepsis bundle: measure lactate, obtain blood cultures before antibiotics, give broad-spectrum antibiotics and 30 mL/kg crystalloid for hypotension or lactate ≥4 mmol/L, start vasopressors for MAP <65 mmHg.

Acid-base stepwise: check pH, then primary disorder by PaCO2 and HCO3, then compensation using Winter formula (expected PaCO2 = 1.5 × HCO3 + 8 ± 2) for metabolic acidosis.

Sodium correction: correct chronic hyponatremia by ≤8-10 mEq/L in 24 hours to avoid osmotic demyelination; symptomatic severe hyponatremia gets hypertonic 3% saline boluses.

Drug monitoring: vancomycin trough 10-20 mcg/mL (15-20 for severe infections); digoxin level 0.5-0.9 ng/mL in heart failure; lithium 0.6-1.2 mEq/L maintenance; warfarin INR 2-3 for most indications.

Biostatistics for practice: number needed to treat = 1/absolute risk reduction; sensitivity rules out disease when negative (SnNout); specificity rules in disease when positive (SpPin); positive predictive value rises with prevalence.

Ethics and documentation: assess decision-making capacity before informed refusal; a patient with capacity may refuse treatment even if the surrogate or family disagrees; report suspected abuse to authorities regardless of confidentiality.

Subject exams are discipline-based (e.g., medicine, surgery, pediatrics, obstetrics-gynecology, psychiatry, family medicine) and use the same vignette style and scoring scale as the CBSE.

Scores are reported as a three-digit scaled score plus a percentile; the passing standard is set per exam form and is not a fixed raw percentage.

Item stems often embed a single discriminating detail (age, time course, medication, travel, occupation); identify that detail before reading the answer choices.

Classic triad and eponym anchors: Beck triad (hypotension, distended neck veins, muffled heart sounds) for tamponade; Charcot triad (fever, jaundice, right upper quadrant pain) for cholangitis; Virchow triad for thrombosis.

Time-course rule: acute onset within minutes to hours suggests vascular or perforation events; days suggests infection or inflammation; weeks to months suggests neoplasm or chronic disease.

Best-next-step questions: choose the intervention that changes management immediately (imaging to confirm a life-threatening diagnosis, or treatment when the diagnosis is already secure) over confirmatory tests that delay care.

Pediatric and obstetric red flags: bilious emesis in a neonate is a surgical emergency; fever in an infant under 28 days requires full sepsis evaluation and hospitalization; painless third-trimester bleeding suggests placenta previa, not a digital exam.

Psychiatry anchors: first-line for schizophrenia is a second-generation antipsychotic; serotonin syndrome (clonus, hyperreflexia, hyperthermia) follows serotonergic combinations; neuroleptic malignant syndrome shows lead-pipe rigidity with elevated creatine kinase.

The IFOM Clinical Science Exam is a comprehensive final-year assessment covering medicine, surgery, pediatrics, obstetrics-gynecology, psychiatry, and public health in an integrated format.

Most IFOM items are single-best-answer with five options; time per item averages roughly 60-90 seconds, so flag long vignettes and return after completing shorter items.

Integrated vignettes require linking basic science mechanism to clinical presentation; expect questions pairing a drug's mechanism with its adverse effect or antidote.

Public health content is examinable: incidence counts new cases over a period at risk; prevalence counts all existing cases; sensitivity and specificity are properties of the test, not the population.

Emergency algorithms to memorize: adult basic and advanced life support rhythms (shockable = ventricular fibrillation and pulseless ventricular tachycardia); anaphylaxis gets intramuscular epinephrine 0.3-0.5 mg of 1:1000 into the anterolateral thigh.

Obstetric calculations: estimated date of delivery by Naegele rule (first day of last menstrual period minus 3 months plus 7 days); gestational age by fundal height between 20 and 36 weeks approximates weeks in centimeters.

Fluid and electrolyte formulas: maintenance fluid by 4-2-1 rule (4 mL/kg/hr for first 10 kg, 2 for next 10, 1 thereafter); corrected sodium = measured sodium + 0.016 × (glucose − 100) in hyperglycemia.

Antimicrobial selection anchors: first-generation cephalosporin for skin flora; ceftriaxone for community-acquired pneumonia and meningitis; piperacillin-tazobactam for broad gram-negative and anaerobic coverage; adjust to culture results.

Autosomal dominant inheritance shows vertical transmission and male-to-male transmission; each child of an affected parent has a 50% risk.

Autosomal recessive inheritance shows a horizontal pattern with 25% recurrence risk per pregnancy; consanguinity increases risk.

X-linked recessive traits show no male-to-male transmission; sons of carrier mothers have a 50% risk and daughters have a 50% chance of being carriers.

Hardy-Weinberg equilibrium: p + q = 1 and p² + 2pq + q² = 1; carrier frequency for a recessive allele is approximately 2q.

Rate-limiting enzymes: phosphofructokinase-1 in glycolysis; fructose-1,6-bisphosphatase in gluconeogenesis; carbamoyl phosphate synthetase I in the urea cycle.

Competitive inhibitors raise Km without changing Vmax; noncompetitive inhibitors lower Vmax without changing Km.

ST-elevation myocardial infarction requires emergent reperfusion, with primary PCI targeted within 90 minutes of first medical contact.

Heart failure with reduced ejection fraction gains mortality benefit from beta-blockers, ACE inhibitors or ARNI, mineralocorticoid receptor antagonists, and SGLT2 inhibitors.

Intravenous alteplase for ischemic stroke is given within 4.5 hours of last known well after noncontrast head CT excludes hemorrhage.

In diabetic ketoacidosis, give IV fluids first and start insulin only after potassium is confirmed above 3.3 mEq/L.

Preeclampsia with severe features is treated with IV magnesium sulfate for seizure prophylaxis plus labetalol, hydralazine, or nifedipine for blood pressure control.

CURB-65 (confusion, urea, respiratory rate, blood pressure, age 65 or older) helps decide inpatient versus outpatient management of community-acquired pneumonia.

Vancomycin target trough is 10-20 mcg/mL, with 15-20 mcg/mL for severe infections such as bacteremia and endocarditis.

Warfarin target INR is 2-3 for most indications and 2.5-3.5 for mechanical mitral valves.

Lithium maintenance levels are typically 0.6-1.2 mEq/L; toxicity risk rises with dehydration and NSAID or thiazide use.

Number needed to treat equals 1 divided by the absolute risk reduction; number needed to harm equals 1 divided by the absolute risk increase.

Winter formula for metabolic acidosis: expected PaCO2 = 1.5 × serum HCO3 + 8, with a margin of plus or minus 2.

Correct chronic hyponatremia by no more than 8-10 mEq/L in 24 hours to prevent osmotic demyelination.

Beck triad of hypotension, distended neck veins, and muffled heart sounds indicates cardiac tamponade.

Charcot triad of fever, jaundice, and right upper quadrant pain indicates ascending cholangitis.

Bilious emesis in a neonate is a surgical emergency suggesting malrotation with volvulus.

Fever in an infant younger than 28 days warrants a full sepsis evaluation and hospitalization.

Painless third-trimester vaginal bleeding suggests placenta previa; a digital cervical exam is contraindicated until it is excluded.

Serotonin syndrome presents with clonus, hyperreflexia, and hyperthermia; neuroleptic malignant syndrome presents with lead-pipe rigidity and elevated creatine kinase.

Incidence counts new cases arising in a population at risk over a period; prevalence counts all existing cases at a point in time.

Sensitivity and specificity are intrinsic test properties; positive and negative predictive values depend on disease prevalence.

Shockable rhythms in advanced life support are ventricular fibrillation and pulseless ventricular tachycardia.

Anaphylaxis is treated with intramuscular epinephrine 0.3-0.5 mg of 1:1000 solution into the anterolateral thigh.

Naegele rule estimates delivery date as first day of last menstrual period minus 3 months plus 7 days.

Maintenance fluid by the 4-2-1 rule: 4 mL/kg/hr for the first 10 kg, 2 mL/kg/hr for the next 10 kg, and 1 mL/kg/hr thereafter.