NBME CBSE EXAM NEWEST 2026/2027
ACTUAL EXAM TEST BANK | NBME CBSE
EXAM REVIEW WITH COMPLETE REAL
EXAM QUESTIONS AND CORRECT
DETAILED ANSWERS (VERIFIED ANSWERS)
ALREADY GRADED A+ (BRAND NEW!!)
Core Domains
• General Principles of Pathology and Cell Biology
• Biochemistry, Molecular Biology, and Genetics
• Immunology and Microbiology
• Pharmacology and Therapeutics
• Cardiovascular, Respiratory, and Renal Systems
• Gastrointestinal, Endocrine, and Reproductive Systems
• Neurology, Psychiatry, and Musculoskeletal Medicine
• Hematology, Biostatistics, and Multisystem Integration
Introduction
The NBME Comprehensive Basic Science Examination (CBSE) is a 200-question,
multiple-choice assessment reflecting USMLE Step 1 content coverage and item
formats . It evaluates integrated basic science knowledge across pathology,
physiology, pharmacology, microbiology, biochemistry, anatomy, and behavioral
sciences. The examination emphasizes application and analysis of foundational
sciences to clinical vignettes. Candidates must demonstrate critical reasoning and
systems-based integration aligned with medical school preclinical curricula.
SECTION ONE: QUESTIONS 1–100
1. A 58-year-old man with a 30-pack-year smoking history presents with a 3-
cm pulmonary mass. Biopsy reveals sheets of malignant cells with scant
cytoplasm, granular “salt-and-pepper” chromatin, and absent nucleoli.
,Numerous mitotic figures and apoptotic bodies are present. Which cellular
process is most directly responsible for the apoptotic bodies observed in this
tumor?
A. Activation of BCL-2 with inhibition of caspase-9
B. Release of cytochrome c from mitochondria with activation of the apoptosome
C. Activation of macrophage nitric oxide synthase causing oncotic necrosis
D. Inhibition of p53 with failure of G1/S checkpoint arrest
B. Release of cytochrome c from mitochondria with activation of the
apoptosome
RATIONALE: Apoptotic bodies are the histologic hallmark of programmed
cell death, mediated by cytochrome c release from mitochondria, apoptosome
assembly (Apaf-1 + caspase-9), and downstream executioner caspases. BCL-2
inhibits apoptosis; p53 inhibition would reduce apoptotic bodies; nitric oxide
mediates necrosis .
2. A 42-year-old woman presents with fatigue and pallor. Laboratory studies
show MCV 78 fL, serum iron low, ferritin low, and TIBC elevated. Which
molecular mechanism most directly accounts for the elevated transferrin
(TIBC) in this patient?
A. Hepcidin-mediated ferroportin degradation is increased
B. Liver transferrin synthesis is upregulated in response to low intracellular iron
stores
C. Defective DMT1 intestinal iron transport causes iron trapping in enterocytes
D. Heme oxygenase-1 degrades heme in macrophages, releasing free iron
B. Liver transferrin synthesis is upregulated in response to low intracellular
iron stores
RATIONALE: In iron-deficiency anemia, low body iron stores stimulate
hepatic transferrin synthesis, causing TIBC to rise. Hepcidin is decreased (not
increased) in iron deficiency, allowing ferroportin-mediated iron export to continue
.
3. A 67-year-old man undergoes an uncomplicated total hip replacement. On
postoperative day 4 he develops dyspnea, tachycardia, and hypoxia. A
ventilation-perfusion scan shows multiple segmental perfusion defects with
normal ventilation. Which inflammatory mediator is most directly responsible
,for the systemic hemodynamic effects (hypotension, tachycardia) seen in this
patient within minutes of the embolic event?
A. Interleukin-6 release from activated T lymphocytes
B. Platelet-activating factor and thromboxane A2 from activated platelets
C. Tumor necrosis factor-alpha from alveolar macrophages
D. Complement C5a-mediated neutrophil chemotaxis
B. Platelet-activating factor and thromboxane A2 from activated platelets
RATIONALE: Acute pulmonary embolism produces rapid hemodynamic
compromise via platelet activation with release of thromboxane A2 and PAF,
causing bronchoconstriction and pulmonary vasoconstriction. IL-6 and TNF-α are
later cytokine responses .
4. A 19-year-old college student is evaluated for recurrent sinopulmonary
infections with encapsulated organisms. Flow cytometry shows absent CD19+
B cells. Which developmental abnormality most likely causes this condition?
A. Failure of thymic epithelial development
B. Defective Bruton tyrosine kinase signaling
C. Defective NADPH oxidase activity
D. Absent adenosine deaminase activity
B. Defective Bruton tyrosine kinase signaling
RATIONALE: X-linked agammaglobulinemia results from BTK mutation,
preventing maturation of B-cell precursors and producing profoundly decreased
immunoglobulins and mature B cells .
5. A 24-year-old medical student is studying the biochemistry of fasting. After
12 hours of fasting, which of the following processes is most increased in the
liver to maintain blood glucose levels?
A. Glycolysis
B. Glycogenesis
C. Glycogenolysis
D. Pentose phosphate pathway
C. Glycogenolysis
, RATIONALE: After 12 hours of fasting, hepatic glycogen stores are mobilized
via glycogenolysis to maintain euglycemia. Glycolysis and glycogenesis are
reduced; the pentose phosphate pathway generates NADPH and ribose-5-
phosphate, not glucose .
6. A 3-day-old neonate presents with poor feeding, vomiting, and lethargy.
Labs show hyperammonemia, respiratory alkalosis, and low BUN. Which
enzyme deficiency is most likely?
A. Ornithine transcarbamylase
B. Fumarase
C. Pyruvate carboxylase
D. Glucose-6-phosphatase
A. Ornithine transcarbamylase
RATIONALE: Ornithine transcarbamylase deficiency is an X-linked urea
cycle disorder presenting in neonates with hyperammonemia, respiratory alkalosis,
and low BUN. Glucose-6-phosphatase deficiency causes von Gierke disease with
hypoglycemia .
7. A 45-year-old man with chronic alcohol use presents with painful, swollen
joints and a history of recurrent kidney stones. Synovial fluid analysis shows
needle-shaped, negatively birefringent crystals. Which metabolic pathway is
most likely impaired?
A. Heme synthesis
B. Purine salvage
C. Pyrimidine catabolism
D. Urea cycle
B. Purine salvage
RATIONALE: Needle-shaped, negatively birefringent crystals indicate gout
due to monosodium urate deposition. Chronic alcohol use and kidney stones
suggest hyperuricemia from impaired purine salvage .
8. A 6-month-old infant presents with developmental delay, coarse facial
features, and hepatosplenomegaly. Enzyme assay reveals deficiency of alpha-
L-iduronidase. Which substances accumulate in lysosomes?
ACTUAL EXAM TEST BANK | NBME CBSE
EXAM REVIEW WITH COMPLETE REAL
EXAM QUESTIONS AND CORRECT
DETAILED ANSWERS (VERIFIED ANSWERS)
ALREADY GRADED A+ (BRAND NEW!!)
Core Domains
• General Principles of Pathology and Cell Biology
• Biochemistry, Molecular Biology, and Genetics
• Immunology and Microbiology
• Pharmacology and Therapeutics
• Cardiovascular, Respiratory, and Renal Systems
• Gastrointestinal, Endocrine, and Reproductive Systems
• Neurology, Psychiatry, and Musculoskeletal Medicine
• Hematology, Biostatistics, and Multisystem Integration
Introduction
The NBME Comprehensive Basic Science Examination (CBSE) is a 200-question,
multiple-choice assessment reflecting USMLE Step 1 content coverage and item
formats . It evaluates integrated basic science knowledge across pathology,
physiology, pharmacology, microbiology, biochemistry, anatomy, and behavioral
sciences. The examination emphasizes application and analysis of foundational
sciences to clinical vignettes. Candidates must demonstrate critical reasoning and
systems-based integration aligned with medical school preclinical curricula.
SECTION ONE: QUESTIONS 1–100
1. A 58-year-old man with a 30-pack-year smoking history presents with a 3-
cm pulmonary mass. Biopsy reveals sheets of malignant cells with scant
cytoplasm, granular “salt-and-pepper” chromatin, and absent nucleoli.
,Numerous mitotic figures and apoptotic bodies are present. Which cellular
process is most directly responsible for the apoptotic bodies observed in this
tumor?
A. Activation of BCL-2 with inhibition of caspase-9
B. Release of cytochrome c from mitochondria with activation of the apoptosome
C. Activation of macrophage nitric oxide synthase causing oncotic necrosis
D. Inhibition of p53 with failure of G1/S checkpoint arrest
B. Release of cytochrome c from mitochondria with activation of the
apoptosome
RATIONALE: Apoptotic bodies are the histologic hallmark of programmed
cell death, mediated by cytochrome c release from mitochondria, apoptosome
assembly (Apaf-1 + caspase-9), and downstream executioner caspases. BCL-2
inhibits apoptosis; p53 inhibition would reduce apoptotic bodies; nitric oxide
mediates necrosis .
2. A 42-year-old woman presents with fatigue and pallor. Laboratory studies
show MCV 78 fL, serum iron low, ferritin low, and TIBC elevated. Which
molecular mechanism most directly accounts for the elevated transferrin
(TIBC) in this patient?
A. Hepcidin-mediated ferroportin degradation is increased
B. Liver transferrin synthesis is upregulated in response to low intracellular iron
stores
C. Defective DMT1 intestinal iron transport causes iron trapping in enterocytes
D. Heme oxygenase-1 degrades heme in macrophages, releasing free iron
B. Liver transferrin synthesis is upregulated in response to low intracellular
iron stores
RATIONALE: In iron-deficiency anemia, low body iron stores stimulate
hepatic transferrin synthesis, causing TIBC to rise. Hepcidin is decreased (not
increased) in iron deficiency, allowing ferroportin-mediated iron export to continue
.
3. A 67-year-old man undergoes an uncomplicated total hip replacement. On
postoperative day 4 he develops dyspnea, tachycardia, and hypoxia. A
ventilation-perfusion scan shows multiple segmental perfusion defects with
normal ventilation. Which inflammatory mediator is most directly responsible
,for the systemic hemodynamic effects (hypotension, tachycardia) seen in this
patient within minutes of the embolic event?
A. Interleukin-6 release from activated T lymphocytes
B. Platelet-activating factor and thromboxane A2 from activated platelets
C. Tumor necrosis factor-alpha from alveolar macrophages
D. Complement C5a-mediated neutrophil chemotaxis
B. Platelet-activating factor and thromboxane A2 from activated platelets
RATIONALE: Acute pulmonary embolism produces rapid hemodynamic
compromise via platelet activation with release of thromboxane A2 and PAF,
causing bronchoconstriction and pulmonary vasoconstriction. IL-6 and TNF-α are
later cytokine responses .
4. A 19-year-old college student is evaluated for recurrent sinopulmonary
infections with encapsulated organisms. Flow cytometry shows absent CD19+
B cells. Which developmental abnormality most likely causes this condition?
A. Failure of thymic epithelial development
B. Defective Bruton tyrosine kinase signaling
C. Defective NADPH oxidase activity
D. Absent adenosine deaminase activity
B. Defective Bruton tyrosine kinase signaling
RATIONALE: X-linked agammaglobulinemia results from BTK mutation,
preventing maturation of B-cell precursors and producing profoundly decreased
immunoglobulins and mature B cells .
5. A 24-year-old medical student is studying the biochemistry of fasting. After
12 hours of fasting, which of the following processes is most increased in the
liver to maintain blood glucose levels?
A. Glycolysis
B. Glycogenesis
C. Glycogenolysis
D. Pentose phosphate pathway
C. Glycogenolysis
, RATIONALE: After 12 hours of fasting, hepatic glycogen stores are mobilized
via glycogenolysis to maintain euglycemia. Glycolysis and glycogenesis are
reduced; the pentose phosphate pathway generates NADPH and ribose-5-
phosphate, not glucose .
6. A 3-day-old neonate presents with poor feeding, vomiting, and lethargy.
Labs show hyperammonemia, respiratory alkalosis, and low BUN. Which
enzyme deficiency is most likely?
A. Ornithine transcarbamylase
B. Fumarase
C. Pyruvate carboxylase
D. Glucose-6-phosphatase
A. Ornithine transcarbamylase
RATIONALE: Ornithine transcarbamylase deficiency is an X-linked urea
cycle disorder presenting in neonates with hyperammonemia, respiratory alkalosis,
and low BUN. Glucose-6-phosphatase deficiency causes von Gierke disease with
hypoglycemia .
7. A 45-year-old man with chronic alcohol use presents with painful, swollen
joints and a history of recurrent kidney stones. Synovial fluid analysis shows
needle-shaped, negatively birefringent crystals. Which metabolic pathway is
most likely impaired?
A. Heme synthesis
B. Purine salvage
C. Pyrimidine catabolism
D. Urea cycle
B. Purine salvage
RATIONALE: Needle-shaped, negatively birefringent crystals indicate gout
due to monosodium urate deposition. Chronic alcohol use and kidney stones
suggest hyperuricemia from impaired purine salvage .
8. A 6-month-old infant presents with developmental delay, coarse facial
features, and hepatosplenomegaly. Enzyme assay reveals deficiency of alpha-
L-iduronidase. Which substances accumulate in lysosomes?
