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NBME CBSE practice questions

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Question 1Behavioral Health

A diagnosis of a major depressive episode requires that the symptoms persist for at least which minimum period?

  1. At least 6 weeks
  2. At least 2 weeks Correct answer.
  3. At least 3 days
  4. At least 3 months

Explanation

A major depressive episode requires five or more symptoms, including depressed mood or anhedonia, present for at least 2 weeks and causing distress or impairment. Shorter durations suggest adjustment reactions or brief mood disturbances rather than a major depressive episode.

Question 2Behavioral Health

Which set of findings is most characteristic of opioid intoxication?

  1. Lateral nystagmus, ataxia, and confusion
  2. Dilated pupils, fever, and marked tachycardia
  3. Tremor, sweating, and piloerection
  4. Pinpoint pupils, slowed breathing, coma Correct answer.

Explanation

Opioid intoxication produces the triad of miosis, respiratory depression, and decreased level of consciousness, and is reversed with naloxone. The other clusters describe anticholinergic or sympathomimetic toxicity, cerebellar toxicity, and opioid withdrawal, respectively.

Question 3Behavioral Health

Which finding is typically the earliest manifestation of alcohol withdrawal?

  1. Wernicke encephalopathy
  2. Tremor and anxiety Correct answer.
  3. Delirium tremens
  4. Grand mal seizures

Explanation

Alcohol withdrawal begins 6 to 24 hours after the last drink with tremor, anxiety, diaphoresis, and autonomic hyperactivity. Seizures typically occur at 12 to 24 hours and delirium tremens at 48 to 96 hours. Wernicke encephalopathy is a nutritional complication, not a withdrawal syndrome.

Question 4Behavioral Health

Which feature distinguishes anorexia nervosa from bulimia nervosa?

  1. Recurrent binge eating
  2. Preoccupation with food
  3. Low body weight Correct answer.
  4. Self-induced vomiting

Explanation

Both disorders share preoccupation with shape and weight and may include binge eating and purging, but anorexia nervosa is defined by significantly low body weight. Bulimia nervosa occurs in individuals at normal or above-normal weight.

Question 5Behavioral Health

To diagnose posttraumatic stress disorder, symptoms must persist for at least which duration?

  1. More than 3 days
  2. More than 1 year
  3. More than 6 months
  4. More than 1 month Correct answer.

Explanation

Posttraumatic stress disorder requires symptoms lasting more than 1 month after exposure to a traumatic event. Symptoms lasting from 3 days to 1 month are classified as acute stress disorder.

Question 6Behavioral Health

A patient taking an SSRI is started on a second serotonergic agent and develops agitation, sweating, and hyperthermia. Which finding most strongly favors serotonin syndrome over neuroleptic malignant syndrome?

  1. Creatine kinase above 1000 U/L
  2. Onset over several days
  3. Inducible clonus and hyperreflexia Correct answer.
  4. Lead-pipe muscle rigidity

Explanation

Serotonin syndrome is characterized by neuromuscular hyperactivity, especially clonus and hyperreflexia, along with autonomic and mental status changes, and it usually evolves rapidly after a serotonergic agent is added. Neuroleptic malignant syndrome instead shows lead-pipe rigidity, bradyreflexia, and marked creatine kinase elevation developing over days.

Question 7Behavioral Health

A patient stable on lithium develops coarse tremor, ataxia, and confusion after several days of vomiting from gastroenteritis. Which factor most likely precipitated the toxicity?

  1. Increased dietary sodium intake
  2. Volume depletion from vomiting Correct answer.
  3. Increased caffeine intake
  4. Occasional acetaminophen use

Explanation

Lithium is excreted renally and is reabsorbed with sodium, so volume depletion causes increased proximal sodium and lithium reabsorption and rising serum levels. Thiazides, NSAIDs, ACE inhibitors, and low-salt diets act similarly.

Question 8Behavioral Health

Which feature best supports delirium rather than dementia as the cause of an older patient's confusion?

  1. Stable course without fluctuation
  2. Preserved attention with isolated memory loss
  3. Acute onset with fluctuating attention Correct answer.
  4. Insidious onset over several years

Explanation

Delirium develops acutely, has a fluctuating course, and is marked by impaired attention and awareness. Dementia has an insidious, progressive course with relatively preserved attention until late stages.

Question 9Behavioral Health

A patient has three panic attacks per week and worries constantly about having another. What is the most appropriate initial treatment?

  1. SSRI with CBT Correct answer.
  2. Standing benzodiazepine monotherapy
  3. An atypical antipsychotic
  4. Propranolol at bedtime

Explanation

Panic disorder responds best to an SSRI combined with cognitive behavioral therapy, which treats both the attacks and the associated anticipatory anxiety. Benzodiazepines are reserved for short-term or crisis use because of dependence risk.

Question 10Behavioral Health

Which factor most strongly predicts a future suicide attempt in a patient with depression?

  1. A prior suicide attempt Correct answer.
  2. Female sex
  3. Age over 60
  4. Being married

Explanation

A previous suicide attempt is the single strongest predictor of eventual completed suicide. Other major risks include male sex, living alone or being widowed, older age in men, and access to lethal means.

Question 11Behavioral Health

A woman 10 days postpartum develops insomnia, confusion, and the belief that her infant would be safer dead. What is the most appropriate next step?

  1. Outpatient therapy with weekly follow-up
  2. Stop breastfeeding and observe at home
  3. Reassurance and sleep hygiene teaching
  4. Urgent psychiatric hospitalization Correct answer.

Explanation

Postpartum psychosis usually emerges within the first 2 weeks after delivery and constitutes a psychiatric emergency because of the risk of suicide and infanticide. It requires inpatient care with antipsychotic treatment and close infant safety planning.

Question 12Behavioral Health

Which finding is most characteristic of neuroleptic malignant syndrome?

  1. Choreoathetoid tongue movements
  2. Sudden neck dystonia within hours
  3. Rigidity with high fever Correct answer.
  4. Fine tremor with hyperreflexia

Explanation

Neuroleptic malignant syndrome presents with lead-pipe rigidity, hyperthermia, autonomic instability, and altered mental status, usually after days of dopamine antagonist exposure. Creatine kinase is elevated, and treatment involves stopping the agent and supportive care with dantrolene or bromocriptine.

Question 13Behavioral Health

A 9-year-old boy has impairing inattention, hyperactivity, and impulsivity at both school and home. Which medication is the most appropriate first-line pharmacotherapy?

  1. Methylphenidate Correct answer.
  2. Fluoxetine for anxiety
  3. Risperidone for mood stabilization
  4. Clonidine as first agent

Explanation

Stimulants such as methylphenidate and amphetamines are first-line pharmacotherapy for school-age children with ADHD, combined with behavioral interventions. Behavioral therapy alone is preferred first for preschool children, and alpha-2 agonists are generally second-line.

Question 14Behavioral Health

Which set of abilities must a patient demonstrate to have decision-making capacity for a treatment choice?

  1. Understanding, appreciation, reasoning, and choice Correct answer.
  2. Agreement with the physician's recommendation
  3. Full orientation to person, place, and time
  4. A Mini-Mental State Examination score above 24

Explanation

Decision-making capacity rests on four elements: the ability to understand the relevant information, appreciate how it applies to oneself, reason about options, and communicate a choice. Capacity is decision-specific and is not equivalent to orientation, a cognitive screening score, or agreeing with the clinician.

Question 15Behavioral Health

A malnourished patient with alcohol use disorder arrives confused and hypoglycemic. Which intervention should be given first?

  1. Intravenous lorazepam
  2. Intravenous thiamine Correct answer.
  3. Intravenous dextrose alone
  4. Oral multivitamins

Explanation

Thiamine should be administered before or alongside glucose in malnourished patients, because a glucose load can precipitate or worsen Wernicke encephalopathy. Thiamine is given empirically whenever the diagnosis is suspected clinically, since treatment is low risk and delay causes lasting deficit.

Question 16Behavioral Health

A patient with severe anorexia nervosa is started on nasogastric feeding. Which electrolyte abnormality most suggests refeeding syndrome?

  1. Hypophosphatemia Correct answer.
  2. Hypernatremia
  3. Hyperkalemia
  4. Hyperphosphatemia

Explanation

Reintroduction of carbohydrate triggers an insulin surge that drives phosphate, potassium, and magnesium intracellularly, producing hypophosphatemia, hypokalemia, and hypomagnesemia. Feeding must start low and advance slowly with electrolyte monitoring and thiamine supplementation.

Question 17Behavioral Health

A patient treated with haloperidol for 8 months develops involuntary tongue and lip movements. Which description best fits this condition?

  1. Acute dystonia responsive to diphenhydramine
  2. Akathisia with inner restlessness
  3. Parkinsonism with cogwheel rigidity
  4. Tardive dyskinesia, often persistent Correct answer.

Explanation

Tardive dyskinesia is a late-onset movement disorder of choreoathetoid oral-facial movements appearing after months of dopamine antagonist exposure, and it may persist after the drug is stopped. Management includes tapering or switching the antipsychotic, and VMAT2 inhibitors may be used.

Question 18Behavioral Health

A patient alternately idealizes and devalues her therapist, reports a shifting sense of self, and has recurrent self-harm. Which treatment is best supported?

  1. Antipsychotic monotherapy
  2. Long-term benzodiazepine therapy
  3. Dialectical behavior therapy Correct answer.
  4. Psychoanalysis focused on early childhood

Explanation

These features suggest borderline personality disorder, for which dialectical behavior therapy is the best-established psychotherapy, targeting emotion dysregulation, self-harm, and interpersonal chaos. Medications are adjunctive and directed at specific symptoms rather than the disorder itself.

Question 19Biostatistics, Epidemiology, and Population Health

A new rapid antigen test is compared with PCR for influenza. Among 200 people with PCR-confirmed influenza, 180 have a positive antigen test. Among 800 people with negative PCR, 80 have a positive antigen test. What is the sensitivity of the antigen test?

  1. 90% Correct answer.
  2. 69%
  3. 10%
  4. 97%

Explanation

Sensitivity is the proportion of truly affected people who test positive: true positives divided by all affected people, or 180/200 = 90%. It is a fixed property of the test and does not depend on prevalence.

Question 20Biostatistics, Epidemiology, and Population Health

A chronic viral infection has a stable incidence. A new drug improves survival but does not cure the infection. Assuming no change in incidence and no migration, what happens to the prevalence of the infection over time?

  1. It falls
  2. It rises Correct answer.
  3. It falls only among treated patients
  4. It remains unchanged

Explanation

Prevalence is approximately incidence multiplied by average duration of disease. Prolonging survival without curing lengthens duration, so prevalence increases even though incidence is unchanged.

Question 21Biostatistics, Epidemiology, and Population Health

Investigators want to identify risk factors for a rare malignancy that has a 20-year latency period. Which study design is most efficient for this purpose?

  1. Cross-sectional survey
  2. Case-control study Correct answer.
  3. Prospective cohort study
  4. Randomized controlled trial

Explanation

A case-control study samples on outcome, starting with people who already have the disease and comparing their past exposures with those of controls. This is efficient for rare diseases with long latency, whereas a cohort would require very large samples and decades of follow-up.

Question 22Biostatistics, Epidemiology, and Population Health

What is the primary purpose of random allocation in a clinical trial?

  1. To balance known and unknown confounders Correct answer.
  2. To ensure the results can be generalized to all patient groups
  3. To guarantee that the trial reaches statistical significance
  4. To prevent observers from knowing the treatment assignment

Explanation

Randomization distributes both measured and unmeasured prognostic factors roughly evenly between groups, which is what allows a causal interpretation of the comparison. Blinding, a separate procedure, addresses observer knowledge, and eligibility criteria govern generalizability.

Question 23Biostatistics, Epidemiology, and Population Health

A trial comparing two antihypertensive drugs reports p = 0.03 for the difference in systolic blood pressure. Which statement best interprets this p-value?

  1. There is a 97% probability that the two drugs truly differ in the population
  2. If there were no true difference, a difference this large would arise 3% of the time Correct answer.
  3. There is only a 3% probability that the null hypothesis of no difference is true in the population
  4. The observed difference has a 3% probability of being clinically important

Explanation

A p-value is the probability of obtaining data at least as extreme as those observed, calculated under the assumption that the null hypothesis is true. It is not the probability that the null hypothesis is true, nor the probability that the finding is clinically important.

Question 24Biostatistics, Epidemiology, and Population Health

A trial is designed with 80% power at a two-sided alpha of 0.05. Which statement describes power?

  1. The probability of a type I error is 0.80
  2. The probability that the null hypothesis is true is 0.80
  3. The proportion of the observed effect explained by treatment
  4. The probability of detecting a true difference of the stated size Correct answer.

Explanation

Power equals 1 minus beta, the probability of rejecting the null hypothesis when a difference of a specified size truly exists. It increases with larger samples, larger effects, and less variability.

Question 25Biostatistics, Epidemiology, and Population Health

A trial reports a mean reduction in LDL cholesterol of 12 mg/dL (95% CI 4 to 20) compared with placebo. Which interpretation is correct?

  1. 95% of participants had a reduction between 4 and 20 mg/dL
  2. The interval excludes zero, so the result is statistically significant Correct answer.
  3. There is a 5% chance that the true reduction lies outside 4 to 20 mg/dL
  4. Repeating the study would give an identical interval 95% of the time

Explanation

A confidence interval describes the range of plausible values for the population parameter. When a 95% interval for a difference excludes the null value of zero, the two-sided test at alpha 0.05 is statistically significant.

Question 26Biostatistics, Epidemiology, and Population Health

In a trial, the 5-year event rate is 20% with placebo and 10% with active treatment. What is the number needed to treat to prevent one event over 5 years?

  1. 10 Correct answer.
  2. 20
  3. 5
  4. 2

Explanation

The absolute risk reduction is 0.20 - 0.10 = 0.10. The number needed to treat is the reciprocal of the absolute risk reduction, 1/0.10 = 10 patients treated for 5 years to prevent one event.

Question 27Biostatistics, Epidemiology, and Population Health

A case-control study of a rare cancer enrolls 100 cases and 100 controls. Forty cases and 20 controls report a history of the exposure of interest. What is the odds ratio?

  1. 2.0
  2. 0.5
  3. 2.7 Correct answer.
  4. 0.17

Explanation

The odds ratio is the cross-product ratio (exposed cases x unexposed controls)/(unexposed cases x exposed controls) = (40 x 80)/(60 x 20) = 2.7. In case-control studies the odds ratio approximates the relative risk when the disease is rare.

Question 28Biostatistics, Epidemiology, and Population Health

Crude all-cause mortality is higher in State A than in State B, but after age adjustment State A's rate is lower. What is the most likely explanation?

  1. State A's mortality records are complete while State B's are not
  2. State A has a less effective health care system
  3. State A has an older population than State B Correct answer.
  4. State B has a much smaller population than State A

Explanation

Age is a strong determinant of mortality and differs between populations, making it a confounder of the crude comparison. Age adjustment removes the effect of differing age composition; a crude rate can be higher purely because a population is older.

Question 29Biostatistics, Epidemiology, and Population Health

A screening program detects a cancer earlier, and survival measured from the date of diagnosis improves. However, the date of death from the cancer is the same as it would have been without screening. Which bias best explains the apparent survival benefit?

  1. Selection bias from nonresponse
  2. Length bias from preferential detection of slow-growing tumors
  3. Lead-time bias Correct answer.
  4. Recall bias in reporting of exposures

Explanation

Lead-time bias occurs when screening moves the date of diagnosis earlier without postponing death, so measured survival from diagnosis lengthens while the actual time of death is unchanged. Mortality in the population, not survival from diagnosis, is the appropriate measure of screening benefit.

Question 30Biostatistics, Epidemiology, and Population Health

Which statement best describes herd immunity?

  1. Enough people are immune that transmission to susceptible people falls Correct answer.
  2. Immunity wanes so rapidly that repeated vaccination is required
  3. Every member of the population must be vaccinated to prevent transmission
  4. Only high-risk groups need to be vaccinated to protect everyone

Explanation

Herd immunity is indirect protection: when a sufficient fraction of the population is immune, chains of transmission are broken and susceptible people are less likely to be exposed. The threshold rises with the basic reproduction number and rarely requires 100% coverage.

Question 31Biostatistics, Epidemiology, and Population Health

A cohort study finds that coffee drinkers have twice the risk of lung cancer. After stratifying by smoking status, the association nearly disappears in every stratum. Smoking is best described as which of the following?

  1. A mediator of the coffee-cancer association
  2. A source of nondifferential misclassification
  3. A confounder of the coffee-cancer association Correct answer.
  4. An effect modifier

Explanation

A confounder is associated with the exposure and with the outcome and does not lie on the causal pathway; it distorts the crude association, and the distortion disappears within strata of the confounder. Smoking is associated with coffee drinking and independently causes lung cancer.

Question 32Biostatistics, Epidemiology, and Population Health

Why do investigators analyze randomized trials by intention to treat?

  1. It eliminates the need for a per-protocol analysis
  2. It preserves the balance created by randomization Correct answer.
  3. It removes the effect of random measurement error
  4. It increases the observed treatment effect and statistical power

Explanation

Intention-to-treat analysis keeps participants in the group to which they were randomized, preserving the prognostic comparability created by randomization. Excluding people who did not adhere introduces selection bias and can exaggerate the apparent benefit.

Question 33Biostatistics, Epidemiology, and Population Health

A test with sensitivity 90% and specificity 90% is applied first in a population with 1% prevalence and then in a population with 20% prevalence. Which change occurs?

  1. Specificity decreases in the high-prevalence population
  2. Negative predictive value is higher in the high-prevalence population
  3. Sensitivity increases in the high-prevalence population
  4. Positive predictive value is higher in the high-prevalence population Correct answer.

Explanation

Positive predictive value depends on prevalence: at 1% prevalence, PPV is about 9/(9+99) = 8%, whereas at 20% prevalence it is about 180/(180+80) = 69%. Sensitivity and specificity are intrinsic test characteristics and do not change with prevalence.

Question 34Biostatistics, Epidemiology, and Population Health

Two radiologists independently classify 100 mammograms. They agree on 90 of them, and agreement expected by chance alone is 60. What is kappa?

  1. 0.75 Correct answer.
  2. 0.60
  3. 0.30
  4. 0.90

Explanation

Kappa is (observed agreement - expected agreement)/(1 - expected agreement) = (0.90 - 0.60)/0.40 = 0.75. It corrects the raw agreement for the agreement that would occur by chance.

Question 35Biostatistics, Epidemiology, and Population Health

At a reception, 60 of 100 guests who ate the potato salad and 10 of 50 guests who did not eat it develop gastroenteritis. What is the attack rate among guests who ate the potato salad?

  1. 20%
  2. 60% Correct answer.
  3. 10%
  4. 50%

Explanation

An attack rate is the proportion of an exposed group that becomes ill: 60 ill among 100 exposed gives 60%. The comparable attack rate among those who did not eat the salad is 10/50 = 20%.

Question 36Biostatistics, Epidemiology, and Population Health

Length of hospital stay is strongly right-skewed because a small number of patients stay for several months. Which measure best summarizes the typical length of stay?

  1. Median Correct answer.
  2. Standard deviation
  3. Range
  4. Mean

Explanation

In a skewed distribution the mean is pulled toward the long tail, whereas the median is resistant to extreme values. The median therefore better represents the typical observation in a right-skewed distribution.

Question 37Blood and Lymphoreticular System

A 38-year-old woman with heavy menstrual bleeding reports fatigue. Which set of laboratory findings is most consistent with iron deficiency anemia?

  1. Increased serum ferritin, decreased total iron-binding capacity, increased mean corpuscular volume
  2. Decreased serum ferritin, increased total iron-binding capacity, decreased mean corpuscular volume Correct answer.
  3. Increased serum ferritin, increased total iron-binding capacity, normal mean corpuscular volume
  4. Decreased serum ferritin, decreased total iron-binding capacity, increased mean corpuscular volume

Explanation

Iron deficiency depletes storage iron (low ferritin), triggers increased hepatic transferrin synthesis (high TIBC), and limits heme synthesis so circulating red cells are small and pale (low MCV). The combination of low ferritin with high TIBC is the classic pattern.

Question 38Blood and Lymphoreticular System

An increase in which of the following shifts the hemoglobin-oxygen dissociation curve to the right, thereby decreasing hemoglobin oxygen affinity?

  1. Fetal hemoglobin
  2. Hemoglobin concentration
  3. Erythrocyte 2,3-bisphosphoglycerate Correct answer.
  4. Blood pH

Explanation

2,3-BPG binds deoxygenated hemoglobin and stabilizes the T (tense) state, lowering oxygen affinity and shifting the curve right so oxygen is unloaded more readily in tissues. This is why chronic hypoxia raises 2,3-BPG and improves tissue oxygen delivery.

Question 39Blood and Lymphoreticular System

A patient with fat malabsorption develops a prolonged prothrombin time that corrects after vitamin K administration. Which of the following factors requires vitamin K-dependent gamma-carboxylation?

  1. Factor VIII
  2. Factor VII Correct answer.
  3. Factor XI
  4. Factor V

Explanation

Factors II, VII, IX, and X together with proteins C and S require vitamin K-dependent gamma-carboxylation of glutamate residues, which allows them to bind calcium and assemble on phospholipid membranes. Factor VII has the shortest half-life, so the PT lengthens first when vitamin K is deficient.

Question 40Blood and Lymphoreticular System

A man of Mediterranean descent develops jaundice and dark urine after taking primaquine. The peripheral smear shows bite cells and Heinz bodies. Which mechanism best explains this finding?

  1. Deficiency of an enzyme that regenerates reduced glutathione Correct answer.
  2. Impaired synthesis of beta-globin chains
  3. Deficiency of spectrin in the red cell membrane skeleton
  4. Autoantibody-mediated destruction of red cells

Explanation

Glucose-6-phosphate dehydrogenase regenerates NADPH, which keeps glutathione reduced; when it is deficient, oxidant drugs overwhelm the cell, hemoglobin precipitates as Heinz bodies, and macrophages bite out the inclusions, leaving bite cells.

Question 41Blood and Lymphoreticular System

Which laboratory finding is characteristically elevated in vitamin B12 deficiency but normal in folate deficiency?

  1. Serum lactate dehydrogenase
  2. Serum methylmalonic acid Correct answer.
  3. Mean corpuscular volume
  4. Serum homocysteine

Explanation

Only cobalamin is required for the methylmalonyl-CoA mutase reaction, so methylmalonic acid accumulates in B12 deficiency but not in folate deficiency. Homocysteine rises in both because both vitamins are needed to remethylate homocysteine to methionine.

Question 42Blood and Lymphoreticular System

A 12-year-old boy has splenomegaly, jaundice, and numerous spherocytes on smear, and his red cells show increased osmotic fragility. Which protein is most likely deficient?

  1. Hemoglobin A2
  2. Spectrin Correct answer.
  3. Pyruvate kinase
  4. Glycophorin A

Explanation

Hereditary spherocytosis most often results from deficiency of spectrin, with or without ankyrin, which destabilizes the membrane skeleton and produces rigid spherocytes that the spleen traps and destroys. Increased osmotic fragility reflects the reduced surface-to-volume ratio of these cells.

Question 43Blood and Lymphoreticular System

A 5-year-old boy has recurrent hemarthroses. His platelet count and prothrombin time are normal, the aPTT is prolonged, and a mixing study with normal plasma corrects the abnormality. Which factor is most likely deficient?

  1. Factor VIII Correct answer.
  2. von Willebrand factor
  3. Factor VII
  4. Factor X

Explanation

A prolonged aPTT with a normal PT and platelet count localizes the defect to the intrinsic pathway (factors VIII, IX, XI, XII), and correction with normal plasma confirms a factor deficiency. Recurrent joint bleeding in a young boy is the typical presentation of factor VIII deficiency.

Question 44Blood and Lymphoreticular System

Which statement best describes the anticoagulant action of unfractionated heparin?

  1. It degrades fibrin polymers into fibrin degradation products
  2. It chelates calcium and thereby blocks the coagulation cascade
  3. It enhances antithrombin-mediated inactivation of thrombin and factor Xa Correct answer.
  4. It inhibits vitamin K epoxide reductase in the liver

Explanation

Heparin binds antithrombin and accelerates its inactivation of thrombin and factor Xa several thousandfold; the effect is monitored with the aPTT. Because it acts on circulating cofactors rather than on synthesis, its onset is immediate.

Question 45Blood and Lymphoreticular System

A patient with gram-negative sepsis develops oozing from venipuncture sites. The platelet count is low, the PT and aPTT are prolonged, fibrinogen is low, and fibrin degradation products are elevated. Which mechanism best explains these findings?

  1. Failure of bone marrow production of platelets
  2. Vitamin K deficiency from biliary obstruction
  3. Autoantibody against platelet glycoprotein IIb/IIIa
  4. Widespread coagulation activation with consumption of platelets and clotting factors Correct answer.

Explanation

In disseminated intravascular coagulation, tissue factor-driven thrombin generation consumes platelets and clotting factors faster than they can be replaced, while secondary fibrinolysis lowers fibrinogen and raises fibrin degradation products. The result is simultaneous thrombosis and bleeding with prolonged PT and aPTT.

Question 46Blood and Lymphoreticular System

A 2-year-old boy has recurrent Staphylococcus aureus and Aspergillus infections. His neutrophils fail to reduce nitroblue tetrazolium. Which process is most likely impaired?

  1. Rolling adhesion of neutrophils to endothelium
  2. Respiratory burst generation of superoxide Correct answer.
  3. Opsonization of bacteria by complement
  4. Chemotaxis toward bacterial peptides

Explanation

NADPH oxidase in phagocytes generates superoxide during the respiratory burst, and its loss causes chronic granulomatous disease, in which catalase-positive organisms cannot be killed and the NBT/DHR test is abnormal. Opsonization and phagocytosis remain intact; the defect is in intracellular killing.

Question 47Blood and Lymphoreticular System

A 22-year-old woman has painless cervical lymphadenopathy and a mediastinal mass. Biopsy shows large binucleate cells with prominent nucleoli that are CD15 and CD30 positive. These neoplastic cells are derived from which cell lineage?

  1. B lymphocytes Correct answer.
  2. Plasma cells
  3. Follicular dendritic cells
  4. Mature T lymphocytes

Explanation

The Reed-Sternberg cells of classic Hodgkin lymphoma are crippled germinal-center B cells that have lost immunoglobulin expression yet retain B-cell transcriptional programming and mark with CD15 and CD30. The surrounding inflammatory infiltrate is reactive, not neoplastic.

Question 48Blood and Lymphoreticular System

A 68-year-old man has back pain, anemia, hypercalcemia, and renal insufficiency. Serum protein electrophoresis shows a narrow spike in the gamma region, and the peripheral smear shows rouleaux. Which process best accounts for these findings?

  1. Proliferation of Reed-Sternberg cells in lymph nodes
  2. Monoclonal proliferation of plasma cells with immunoglobulin secretion Correct answer.
  3. Polyclonal B-cell activation in response to chronic infection
  4. Clonal proliferation of mature T cells within the skin

Explanation

Multiple myeloma is a clonal plasma cell neoplasm that secretes a monoclonal immunoglobulin (the M spike), replaces marrow to cause anemia and lytic bone lesions, and raises the serum protein enough to produce rouleaux. Hypercalcemia follows cytokine-driven bone resorption.

Question 49Blood and Lymphoreticular System

A 28-year-old woman who is Rh-negative delivers an Rh-positive infant and becomes sensitized. In a subsequent pregnancy with an Rh-positive fetus, which antibody is responsible for fetal hemolysis?

  1. Maternal IgM anti-A
  2. Maternal IgG anti-D that crosses the placenta Correct answer.
  3. Fetal IgG directed against maternal red cells
  4. Maternal IgA anti-D secreted in breast milk

Explanation

Only IgG is transported across the placenta, so IgG anti-D coats fetal Rh-positive red cells and causes extravascular hemolysis with anemia, jaundice, and hydrops in severe cases. IgM antibodies such as anti-A and anti-B cannot cross, which is why ABO incompatibility is usually mild.

Question 50Blood and Lymphoreticular System

A 25-year-old man presents with fatigue and bruising. He has pancytopenia with a low reticulocyte count, no hepatosplenomegaly, and a marrow biopsy that is largely replaced by fat. Which diagnosis is most likely?

  1. Megaloblastic anemia
  2. Primary myelofibrosis
  3. Acute myeloid leukemia
  4. Aplastic anemia Correct answer.

Explanation

Pancytopenia with reticulocytopenia and an empty, fatty marrow in the absence of organomegaly is the hallmark of aplastic anemia, a failure of hematopoietic stem cells. Peripheral destruction would raise the reticulocyte count, and infiltration would enlarge organs.