NBME CBSE ACTUAL TEST
QUESTIONS AND ANSWERS
200 Questions | 2026/2027 Updated
Comprehensive Basic Science Examination
Comprehensive Test Bank - 9 Sections
Aligned with 2026-2027 NBME CBSE Content Outline
Step 1 Level Integration of Basic Science Concepts
COMPREHENSIVE CONTENT COVERAGE
Biochemistry & Molecular Biology | Microbiology & Immunology
Pathology & Pathophysiology | Pharmacology | Physiology
Anatomy & Embryology | Behavioral Science & Biostatistics
Organ Systems Integration | High-Yield Clinical Vignettes
EXAM DESIGN SPECIFICATIONS
Total Questions: 200 | Format: Multiple Choice (A-D) | Sections: 9
Cognitive Levels: 30% Recall | 50% Application | 20% Analysis
Question Style: 85% Clinical Vignette-Based | 15% Direct Recall
Each Question: 100% Correct Answer + Detailed Medical Science Rationale
NBME-style clinical vignettes with patient presentation, lab findings, & next best step
2026/2027 updates: current medical knowledge, NBME exam standards, & Step 1 integration
Prepared for Medical Student Education | NBME CBSE Preparation
Comprehensive Test Bank with Verified Correct Answers and Detailed Rationales
,NBME CBSE Actual Test | 200 Questions & Answers | 2026/2027 Updated Page 2
NBME CBSE ACTUAL TEST
200 Questions and Answers - 2026/2027 Updated
This comprehensive test bank is designed to prepare medical students for the NBME Comprehensive Basic
Science Examination (CBSE) with complete coverage across nine content domains aligned with the 2026-2027
NBME content outline and USMLE Step 1 integration. Each of the 200 questions has been constructed to
mirror the rigor and format of the official NBME examination, with eighty-five percent of items presented as
clinical vignette-based scenarios and fifteen percent as direct recall. Cognitive distribution targets thirty percent
recall, fifty percent application, and twenty percent analysis, reflecting medical student basic science
competency and clinical reasoning.
Each question includes the correct answer, the full text of the correct choice, and a detailed rationale explaining
the medical science reasoning including pathophysiological mechanisms, clinical correlations, and NBME-style
explanations. Distractors are constructed to represent common medical student errors including confusing
similar diseases, misinterpreting lab values, incorrect drug mechanisms, statistical calculation errors, and
pathophysiological misconceptions. High-yield NBME concepts are emphasized across all basic science
disciplines with commonly confused concept pairs (Type I vs. Type II errors, Sensitivity vs. Specificity,
Necrosis vs. Apoptosis). This test bank serves as both a study resource and a self-assessment tool for NBME
CBSE success.
Section Overview
Section 1 Q1-20 Biochemistry and Molecular Biology
Section 2 Q21-40 Microbiology and Immunology
Section 3 Q41-65 Pathology and Pathophysiology
Section 4 Q66-85 Pharmacology
Section 5 Q86-110 Physiology
Section 6 Q111-130 Anatomy and Embryology
Section 7 Q131-145 Behavioral Science and Biostatistics
Section 8 Q146-175 Organ Systems Integration
Section 9 Q176-200 High-Yield Clinical Vignettes
NBME Comprehensive Basic Science Examination | 2026/2027 Actual Test Bank
,NBME CBSE Actual Test | 200 Questions & Answers | 2026/2027 Updated Page 3
SECTION 1: Biochemistry and Molecular Biology
Q1-Q20 | Enzymes, Metabolism, Molecular Genetics, & Cell Biology | 30% Recall | 50% Application | 20% Analysis
Vignette: A 24-year-old man presents with fatigue, jaundice, and dark urine after taking primaquine for malaria
prophylaxis. Labs show hemoglobin 8.0 g/dL, low haptoglobin, elevated indirect bilirubin, and Heinz bodies on
peripheral smear.
Q1: Which enzyme deficiency is most likely responsible for this patient's condition?
A. Pyruvate kinase
B. Glucose-6-phosphate dehydrogenase (G6PD) [CORRECT]
C. Hexokinase
D. Glucokinase
Correct Answer: B
Rationale: G6PD deficiency is an X-linked disorder causing reduced NADPH production in the hexose
monophosphate shunt. Without NADPH, glutathione cannot be reduced, leading to oxidative damage (Heinz bodies)
and hemolysis after exposure to oxidative stress (primaquine, fava beans, sulfa drugs, infections). Pyruvate kinase
deficiency causes chronic hemolytic anemia but not Heinz bodies. NGN strategy: oxidative hemolysis + Heinz bodies
= G6PD deficiency.
Vignette: A 6-month-old infant of Ashkenazi Jewish descent presents with developmental delay,
hepatosplenomegaly, and a cherry-red spot on macular examination.
Q2: Which enzyme deficiency is most likely responsible?
A. Hexosaminidase A [CORRECT]
B. Glucocerebrosidase
C. Sphingomyelinase
D. Alpha-galactosidase A
Correct Answer: A
Rationale: Tay-Sachs disease is caused by hexosaminidase A deficiency (autosomal recessive, chromosome 15),
leading to GM2 ganglioside accumulation in neurons. Classic features: developmental delay, cherry-red macular spot,
no hepatosplenomegaly (distinguishes from Niemann-Pick/Gaucher). Death in early childhood. NGN strategy:
cherry-red spot + no hepatosplenomegaly = Tay-Sachs.
Vignette: A 30-year-old man of Northern European descent presents with early-onset Parkinson disease, corneal
arcus, and hepatosplenomegaly. Bone marrow biopsy shows lipid-laden macrophages (Gaucher cells).
Q3: Which enzyme deficiency is responsible for this condition?
A. Glucocerebrosidase [CORRECT]
B. Sphingomyelinase
C. Alpha-galactosidase A
D. Hexosaminidase A
Correct Answer: A
Rationale: Gaucher disease (most common lysosomal storage disorder) is caused by glucocerebrosidase deficiency,
leading to glucocerebroside accumulation in macrophages (Gaucher cells - 'crumpled tissue paper' appearance).
Features: hepatosplenomegaly, pancytopenia, bone pain, aseptic necrosis of femur. Treatment: enzyme replacement
(imiglucerase). NGN strategy: Gaucher cells + hepatosplenomegaly = glucocerebrosidase.
NBME Comprehensive Basic Science Examination | 2026/2027 Actual Test Bank
, NBME CBSE Actual Test | 200 Questions & Answers | 2026/2027 Updated Page 4
Vignette: A 45-year-old man presents with a myocardial infarction. Family history reveals relatives with
early-onset coronary artery disease. Laboratory testing reveals elevated LDL cholesterol.
Q4: Which receptor defect is most likely responsible for this patient's hypercholesterolemia?
A. LDL receptor deficiency [CORRECT]
B. Lipoprotein lipase deficiency
C. Apolipoprotein B-100 defect
D. HMG-CoA reductase deficiency
Correct Answer: A
Rationale: Familial hypercholesterolemia (FH) is an autosomal dominant disorder caused by LDL receptor deficiency
(or defective ApoB-100), leading to elevated LDL cholesterol and premature atherosclerosis. Heterozygotes (1:500)
have LDL 200-400; homozygotes (1:1,000,000) have LDL >500 with cutaneous xanthomas by age 10. Treatment:
statins, PCSK9 inhibitors. NGN strategy: early CAD + high LDL = FH.
Vignette: A 3-day-old infant presents with poor feeding, vomiting, lethargy, and seizures. Lab tests reveal
metabolic acidosis with elevated anion gap, ketonuria, and elevated propionic acid.
Q5: Which vitamin deficiency is most likely responsible if this patient has a cobalamin (B12) responsive
disorder?
A. Thiamine (B1)
B. Riboflavin (B2)
C. Cobalamin (B12) [CORRECT]
D. Folate (B9)
Correct Answer: C
Rationale: Cobalamin (B12) is a cofactor for methylmalonyl-CoA mutase (converts methylmalonyl-CoA to
succinyl-CoA). Deficiency (or inborn errors) causes methylmalonic acidemia/aciduria with metabolic acidosis, ketosis,
and hyperammonemia. Treatment: B12 supplementation, low-protein diet. Folate deficiency causes megaloblastic
anemia without neurologic symptoms. NGN strategy: metabolic acidosis + ketosis + elevated propionic/methylmalonic
acid = B12-related disorder.
Vignette: A 50-year-old chronic alcoholic presents with confusion, ataxia, nystagmus, and ophthalmoplegia.
Q6: Which vitamin deficiency is responsible for this patient's condition?
A. Thiamine (B1) [CORRECT]
B. Niacin (B3)
C. Pyridoxine (B6)
D. Cobalamin (B12)
Correct Answer: A
Rationale: Wernicke-Korsakoff syndrome is caused by thiamine (B1) deficiency, common in chronic alcoholics.
Wernicke encephalopathy: confusion, ataxia, nystagmus, ophthalmoplegia (acute, reversible with IV thiamine).
Korsakoff psychosis: anterograde and retrograde amnesia, confabulation (chronic, irreversible). Thiamine is cofactor
for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, transketolase. NGN strategy: alcoholic +
confusion/ataxia/nystagmus = Wernicke = thiamine.
Vignette: A 40-year-old man presents with pellagra (dermatitis, diarrhea, dementia) and glossitis. He has a diet
high in corn.
NBME Comprehensive Basic Science Examination | 2026/2027 Actual Test Bank
QUESTIONS AND ANSWERS
200 Questions | 2026/2027 Updated
Comprehensive Basic Science Examination
Comprehensive Test Bank - 9 Sections
Aligned with 2026-2027 NBME CBSE Content Outline
Step 1 Level Integration of Basic Science Concepts
COMPREHENSIVE CONTENT COVERAGE
Biochemistry & Molecular Biology | Microbiology & Immunology
Pathology & Pathophysiology | Pharmacology | Physiology
Anatomy & Embryology | Behavioral Science & Biostatistics
Organ Systems Integration | High-Yield Clinical Vignettes
EXAM DESIGN SPECIFICATIONS
Total Questions: 200 | Format: Multiple Choice (A-D) | Sections: 9
Cognitive Levels: 30% Recall | 50% Application | 20% Analysis
Question Style: 85% Clinical Vignette-Based | 15% Direct Recall
Each Question: 100% Correct Answer + Detailed Medical Science Rationale
NBME-style clinical vignettes with patient presentation, lab findings, & next best step
2026/2027 updates: current medical knowledge, NBME exam standards, & Step 1 integration
Prepared for Medical Student Education | NBME CBSE Preparation
Comprehensive Test Bank with Verified Correct Answers and Detailed Rationales
,NBME CBSE Actual Test | 200 Questions & Answers | 2026/2027 Updated Page 2
NBME CBSE ACTUAL TEST
200 Questions and Answers - 2026/2027 Updated
This comprehensive test bank is designed to prepare medical students for the NBME Comprehensive Basic
Science Examination (CBSE) with complete coverage across nine content domains aligned with the 2026-2027
NBME content outline and USMLE Step 1 integration. Each of the 200 questions has been constructed to
mirror the rigor and format of the official NBME examination, with eighty-five percent of items presented as
clinical vignette-based scenarios and fifteen percent as direct recall. Cognitive distribution targets thirty percent
recall, fifty percent application, and twenty percent analysis, reflecting medical student basic science
competency and clinical reasoning.
Each question includes the correct answer, the full text of the correct choice, and a detailed rationale explaining
the medical science reasoning including pathophysiological mechanisms, clinical correlations, and NBME-style
explanations. Distractors are constructed to represent common medical student errors including confusing
similar diseases, misinterpreting lab values, incorrect drug mechanisms, statistical calculation errors, and
pathophysiological misconceptions. High-yield NBME concepts are emphasized across all basic science
disciplines with commonly confused concept pairs (Type I vs. Type II errors, Sensitivity vs. Specificity,
Necrosis vs. Apoptosis). This test bank serves as both a study resource and a self-assessment tool for NBME
CBSE success.
Section Overview
Section 1 Q1-20 Biochemistry and Molecular Biology
Section 2 Q21-40 Microbiology and Immunology
Section 3 Q41-65 Pathology and Pathophysiology
Section 4 Q66-85 Pharmacology
Section 5 Q86-110 Physiology
Section 6 Q111-130 Anatomy and Embryology
Section 7 Q131-145 Behavioral Science and Biostatistics
Section 8 Q146-175 Organ Systems Integration
Section 9 Q176-200 High-Yield Clinical Vignettes
NBME Comprehensive Basic Science Examination | 2026/2027 Actual Test Bank
,NBME CBSE Actual Test | 200 Questions & Answers | 2026/2027 Updated Page 3
SECTION 1: Biochemistry and Molecular Biology
Q1-Q20 | Enzymes, Metabolism, Molecular Genetics, & Cell Biology | 30% Recall | 50% Application | 20% Analysis
Vignette: A 24-year-old man presents with fatigue, jaundice, and dark urine after taking primaquine for malaria
prophylaxis. Labs show hemoglobin 8.0 g/dL, low haptoglobin, elevated indirect bilirubin, and Heinz bodies on
peripheral smear.
Q1: Which enzyme deficiency is most likely responsible for this patient's condition?
A. Pyruvate kinase
B. Glucose-6-phosphate dehydrogenase (G6PD) [CORRECT]
C. Hexokinase
D. Glucokinase
Correct Answer: B
Rationale: G6PD deficiency is an X-linked disorder causing reduced NADPH production in the hexose
monophosphate shunt. Without NADPH, glutathione cannot be reduced, leading to oxidative damage (Heinz bodies)
and hemolysis after exposure to oxidative stress (primaquine, fava beans, sulfa drugs, infections). Pyruvate kinase
deficiency causes chronic hemolytic anemia but not Heinz bodies. NGN strategy: oxidative hemolysis + Heinz bodies
= G6PD deficiency.
Vignette: A 6-month-old infant of Ashkenazi Jewish descent presents with developmental delay,
hepatosplenomegaly, and a cherry-red spot on macular examination.
Q2: Which enzyme deficiency is most likely responsible?
A. Hexosaminidase A [CORRECT]
B. Glucocerebrosidase
C. Sphingomyelinase
D. Alpha-galactosidase A
Correct Answer: A
Rationale: Tay-Sachs disease is caused by hexosaminidase A deficiency (autosomal recessive, chromosome 15),
leading to GM2 ganglioside accumulation in neurons. Classic features: developmental delay, cherry-red macular spot,
no hepatosplenomegaly (distinguishes from Niemann-Pick/Gaucher). Death in early childhood. NGN strategy:
cherry-red spot + no hepatosplenomegaly = Tay-Sachs.
Vignette: A 30-year-old man of Northern European descent presents with early-onset Parkinson disease, corneal
arcus, and hepatosplenomegaly. Bone marrow biopsy shows lipid-laden macrophages (Gaucher cells).
Q3: Which enzyme deficiency is responsible for this condition?
A. Glucocerebrosidase [CORRECT]
B. Sphingomyelinase
C. Alpha-galactosidase A
D. Hexosaminidase A
Correct Answer: A
Rationale: Gaucher disease (most common lysosomal storage disorder) is caused by glucocerebrosidase deficiency,
leading to glucocerebroside accumulation in macrophages (Gaucher cells - 'crumpled tissue paper' appearance).
Features: hepatosplenomegaly, pancytopenia, bone pain, aseptic necrosis of femur. Treatment: enzyme replacement
(imiglucerase). NGN strategy: Gaucher cells + hepatosplenomegaly = glucocerebrosidase.
NBME Comprehensive Basic Science Examination | 2026/2027 Actual Test Bank
, NBME CBSE Actual Test | 200 Questions & Answers | 2026/2027 Updated Page 4
Vignette: A 45-year-old man presents with a myocardial infarction. Family history reveals relatives with
early-onset coronary artery disease. Laboratory testing reveals elevated LDL cholesterol.
Q4: Which receptor defect is most likely responsible for this patient's hypercholesterolemia?
A. LDL receptor deficiency [CORRECT]
B. Lipoprotein lipase deficiency
C. Apolipoprotein B-100 defect
D. HMG-CoA reductase deficiency
Correct Answer: A
Rationale: Familial hypercholesterolemia (FH) is an autosomal dominant disorder caused by LDL receptor deficiency
(or defective ApoB-100), leading to elevated LDL cholesterol and premature atherosclerosis. Heterozygotes (1:500)
have LDL 200-400; homozygotes (1:1,000,000) have LDL >500 with cutaneous xanthomas by age 10. Treatment:
statins, PCSK9 inhibitors. NGN strategy: early CAD + high LDL = FH.
Vignette: A 3-day-old infant presents with poor feeding, vomiting, lethargy, and seizures. Lab tests reveal
metabolic acidosis with elevated anion gap, ketonuria, and elevated propionic acid.
Q5: Which vitamin deficiency is most likely responsible if this patient has a cobalamin (B12) responsive
disorder?
A. Thiamine (B1)
B. Riboflavin (B2)
C. Cobalamin (B12) [CORRECT]
D. Folate (B9)
Correct Answer: C
Rationale: Cobalamin (B12) is a cofactor for methylmalonyl-CoA mutase (converts methylmalonyl-CoA to
succinyl-CoA). Deficiency (or inborn errors) causes methylmalonic acidemia/aciduria with metabolic acidosis, ketosis,
and hyperammonemia. Treatment: B12 supplementation, low-protein diet. Folate deficiency causes megaloblastic
anemia without neurologic symptoms. NGN strategy: metabolic acidosis + ketosis + elevated propionic/methylmalonic
acid = B12-related disorder.
Vignette: A 50-year-old chronic alcoholic presents with confusion, ataxia, nystagmus, and ophthalmoplegia.
Q6: Which vitamin deficiency is responsible for this patient's condition?
A. Thiamine (B1) [CORRECT]
B. Niacin (B3)
C. Pyridoxine (B6)
D. Cobalamin (B12)
Correct Answer: A
Rationale: Wernicke-Korsakoff syndrome is caused by thiamine (B1) deficiency, common in chronic alcoholics.
Wernicke encephalopathy: confusion, ataxia, nystagmus, ophthalmoplegia (acute, reversible with IV thiamine).
Korsakoff psychosis: anterograde and retrograde amnesia, confabulation (chronic, irreversible). Thiamine is cofactor
for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase, transketolase. NGN strategy: alcoholic +
confusion/ataxia/nystagmus = Wernicke = thiamine.
Vignette: A 40-year-old man presents with pellagra (dermatitis, diarrhea, dementia) and glossitis. He has a diet
high in corn.
NBME Comprehensive Basic Science Examination | 2026/2027 Actual Test Bank
