NBME CBSSA flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Autosomal dominant recurrence risk

Each child of an affected heterozygous parent has a 50% chance of inheriting the allele. Male-to-male transmission occurs, and the pedigree shows vertical transmission across generations.

Autosomal recessive recurrence risk

Two carrier parents have a 25% chance per pregnancy of an affected child, 50% chance of a carrier child, and 25% chance of an unaffected noncarrier child.

X-linked recessive inheritance

No male-to-male transmission occurs. Sons of carrier mothers have a 50% risk of disease, and daughters have a 50% chance of being carriers.

Hardy-Weinberg carrier frequency

For a recessive allele with frequency q, carrier frequency is 2pq, which approximates 2q when q is small. Disease frequency is q squared.

Competitive inhibition kinetics

A competitive inhibitor binds the active site reversibly, raising apparent Km while leaving Vmax unchanged because high substrate concentration can outcompete the inhibitor.

Rate-limiting enzyme of glycolysis

Phosphofructokinase-1 catalyzes the committed step of glycolysis and is activated by AMP and fructose-2,6-bisphosphate and inhibited by ATP and citrate.

Oxygen dissociation curve right shift

Increased 2,3-BPG, carbon dioxide, hydrogen ion, and temperature decrease hemoglobin oxygen affinity, shifting the curve right and favoring oxygen unloading in tissues.

Diphtheria toxin mechanism

Diphtheria exotoxin ADP-ribosylates elongation factor 2, halting protein synthesis and causing pseudomembranous pharyngitis, myocarditis, and neuropathy.

STEMI reperfusion target

Primary percutaneous coronary intervention should be performed within 90 minutes of first medical contact for ST-elevation myocardial infarction, or fibrinolysis if transfer delays exceed that window.

Heart failure reduced ejection fraction therapy

Mortality benefit comes from beta-blockers, ACE inhibitors, ARBs, or ARNI, mineralocorticoid receptor antagonists, and SGLT2 inhibitors. Loop diuretics relieve congestion without mortality benefit.

Stroke thrombolysis window

Intravenous alteplase may be given within 4.5 hours of last known well after noncontrast head CT excludes intracranial hemorrhage and blood pressure is controlled.

DKA insulin and potassium order

Give IV fluids first. Start insulin infusion only when serum potassium is above 3.3 mEq/L, because insulin drives potassium intracellularly and total body potassium is already depleted.

Preeclampsia severe features treatment

IV magnesium sulfate prevents and treats eclamptic seizures; labetalol, hydralazine, or nifedipine control severe hypertension. Delivery is the definitive treatment.

CURB-65 components

Confusion, urea above 7 mmol/L, respiratory rate 30 or higher, low blood pressure, and age 65 or older. Higher scores predict mortality and support inpatient admission.

Infant developmental milestones

Social smile at 6 weeks, head control at 3 months, sitting unsupported at 6 to 8 months, walking at 12 to 15 months, and two-word phrases by 18 to 24 months.

Colorectal cancer screening start

Average-risk adults begin screening at age 45, with colonoscopy every 10 years or annual stool-based testing as alternatives.

Vancomycin therapeutic trough

Target trough is 10 to 20 mcg/mL, with 15 to 20 mcg/mL recommended for severe infections such as bacteremia, endocarditis, and osteomyelitis.

Warfarin INR targets

INR 2 to 3 for most indications including atrial fibrillation and venous thromboembolism; INR 2.5 to 3.5 for mechanical mitral valves.

Number needed to treat

NNT equals 1 divided by the absolute risk reduction. It expresses how many patients must be treated for one additional patient to benefit.

Winter formula compensation

In metabolic acidosis, expected PaCO2 equals 1.5 times serum bicarbonate plus 8, with a margin of plus or minus 2. Values outside this range indicate a mixed disorder.

Chronic hyponatremia correction limit

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

Sepsis initial resuscitation bundle

Measure lactate, draw blood cultures before antibiotics, give broad-spectrum antibiotics and 30 mL/kg crystalloid for hypotension or lactate 4 mmol/L or higher, then vasopressors for MAP below 65 mmHg.

Lithium therapeutic range

Maintenance serum lithium is typically 0.6 to 1.2 mEq/L. Toxicity risk increases with dehydration and with NSAID, thiazide, or ACE inhibitor use.

Digoxin level in heart failure

Target serum digoxin is 0.5 to 0.9 ng/mL in heart failure. Higher levels increase toxicity without added benefit.

Beck triad

Hypotension, distended neck veins, and muffled heart sounds indicate cardiac tamponade, which requires urgent pericardiocentesis.

Charcot triad

Fever, jaundice, and right upper quadrant pain indicate ascending cholangitis, typically from an obstructing common bile duct stone requiring antibiotics and drainage.

Neonatal bilious emesis

Bilious vomiting in a neonate is a surgical emergency suggesting malrotation with volvulus or intestinal atresia until proven otherwise.

Young infant fever rule

Fever of 38 degrees Celsius or higher in an infant younger than 28 days requires a full sepsis evaluation and hospitalization with empiric antibiotics.

Serotonin versus neuroleptic malignant

Serotonin syndrome shows clonus, hyperreflexia, and hyperthermia after serotonergic drugs. Neuroleptic malignant syndrome shows lead-pipe rigidity, bradyreflexia, and elevated creatine kinase after dopamine antagonists.

Incidence versus prevalence

Incidence counts new cases in a population at risk over a period. Prevalence counts all existing cases at a point in time and rises with longer disease duration.

Sensitivity and predictive value

Sensitivity and specificity are intrinsic test properties. Positive and negative predictive values depend on disease prevalence in the tested population.

Anaphylaxis epinephrine dose

Give intramuscular epinephrine 0.3 to 0.5 mg of 1:1000 solution into the anterolateral thigh, repeating every 5 to 15 minutes as needed.