NBME Comprehensive Basic Science
Examination (CBSE) Questions And Correct
Answers (Verified Answers) Plus Rationales
2025/2026 Q&A | Instant Download Pdf
1. A 25-year-old man presents with severe abdominal pain and
vomiting. Lab tests reveal hypercalcemia and elevated parathyroid
hormone. Which of the following is the most likely cause?
A) Hyperthyroidism
B) Primary hyperparathyroidism
C) Addison’s disease
D) Hypoparathyroidism
Answer: B) Primary hyperparathyroidism
Rationale: Elevated calcium and elevated PTH indicate primary
hyperparathyroidism. Hyperthyroidism increases calcium but
suppresses PTH; Addison’s affects sodium/potassium;
hypoparathyroidism decreases calcium.
2. Which enzyme deficiency is most commonly associated with
hemolytic anemia after fava bean ingestion?
A) Glucose-6-phosphate dehydrogenase (G6PD)
B) Pyruvate kinase
C) Hexokinase
D) Glutathione peroxidase
Answer: A) Glucose-6-phosphate dehydrogenase (G6PD)
Rationale: G6PD deficiency reduces NADPH, impairing protection
against oxidative stress. Fava beans contain oxidants that precipitate
hemolysis in G6PD-deficient patients.
,3. A patient presents with tremor, weight loss, and heat intolerance.
Lab tests reveal decreased TSH. What is the most likely diagnosis?
A) Hypothyroidism
B) Graves’ disease
C) Hashimoto thyroiditis
D) Secondary hypothyroidism
Answer: B) Graves’ disease
Rationale: Low TSH and symptoms of hyperthyroidism suggest
Graves’ disease, an autoimmune cause of hyperthyroidism.
4. Which vitamin deficiency causes beriberi?
A) Vitamin B1
B) Vitamin B2
C) Vitamin B3
D) Vitamin B12
Answer: A) Vitamin B1
Rationale: Thiamine (B1) deficiency causes beriberi, affecting the
cardiovascular and nervous systems.
5. A patient has prolonged bleeding time but normal PT and aPTT.
Which factor is most likely defective?
A) Factor VIII
B) Platelets
C) Factor VII
D) Factor IX
Answer: B) Platelets
Rationale: Prolonged bleeding time with normal PT and aPTT
indicates a platelet defect, not a coagulation factor deficiency.
,6. Which neurotransmitter is primarily deficient in Parkinson’s
disease?
A) Acetylcholine
B) Dopamine
C) Serotonin
D) GABA
Answer: B) Dopamine
Rationale: Parkinson’s disease is characterized by degeneration of
dopaminergic neurons in the substantia nigra.
7. A patient with a high fever, cough, and rusty-colored sputum most
likely has:
A) Mycoplasma pneumonia
B) Pneumococcal pneumonia
C) Klebsiella pneumonia
D) Legionella pneumonia
Answer: B) Pneumococcal pneumonia
Rationale: Streptococcus pneumoniae is the most common cause of
community-acquired pneumonia and produces rusty sputum.
8. A 45-year-old man presents with jaundice, dark urine, and pale
stools. Which lab pattern is most consistent with obstructive
jaundice?
A) High unconjugated bilirubin
B) High conjugated bilirubin, elevated ALP
C) Low total bilirubin
D) High AST/ALT only
Answer: B) High conjugated bilirubin, elevated ALP
Rationale: Obstruction causes conjugated hyperbilirubinemia and
cholestatic enzymes (ALP, GGT) elevation.
, 9. Which type of hypersensitivity is mediated by IgE?
A) Type I
B) Type II
C) Type III
D) Type IV
Answer: A) Type I
Rationale: Type I hypersensitivity reactions involve IgE-mediated
mast cell degranulation (e.g., anaphylaxis, allergies).
10. Which structure forms the blood-brain barrier?
A) Astrocyte end-feet
B) Microglia
C) Neuronal cell bodies
D) Ependymal cells
Answer: A) Astrocyte end-feet
Rationale: Astrocytes contribute to the tight junctions of endothelial
cells, forming the blood-brain barrier.
11. Which cell type is primarily responsible for humoral immunity?
A) T cells
B) B cells
C) NK cells
D) Macrophages
Answer: B) B cells
Rationale: B cells differentiate into plasma cells that produce
antibodies, mediating humoral immunity.
Examination (CBSE) Questions And Correct
Answers (Verified Answers) Plus Rationales
2025/2026 Q&A | Instant Download Pdf
1. A 25-year-old man presents with severe abdominal pain and
vomiting. Lab tests reveal hypercalcemia and elevated parathyroid
hormone. Which of the following is the most likely cause?
A) Hyperthyroidism
B) Primary hyperparathyroidism
C) Addison’s disease
D) Hypoparathyroidism
Answer: B) Primary hyperparathyroidism
Rationale: Elevated calcium and elevated PTH indicate primary
hyperparathyroidism. Hyperthyroidism increases calcium but
suppresses PTH; Addison’s affects sodium/potassium;
hypoparathyroidism decreases calcium.
2. Which enzyme deficiency is most commonly associated with
hemolytic anemia after fava bean ingestion?
A) Glucose-6-phosphate dehydrogenase (G6PD)
B) Pyruvate kinase
C) Hexokinase
D) Glutathione peroxidase
Answer: A) Glucose-6-phosphate dehydrogenase (G6PD)
Rationale: G6PD deficiency reduces NADPH, impairing protection
against oxidative stress. Fava beans contain oxidants that precipitate
hemolysis in G6PD-deficient patients.
,3. A patient presents with tremor, weight loss, and heat intolerance.
Lab tests reveal decreased TSH. What is the most likely diagnosis?
A) Hypothyroidism
B) Graves’ disease
C) Hashimoto thyroiditis
D) Secondary hypothyroidism
Answer: B) Graves’ disease
Rationale: Low TSH and symptoms of hyperthyroidism suggest
Graves’ disease, an autoimmune cause of hyperthyroidism.
4. Which vitamin deficiency causes beriberi?
A) Vitamin B1
B) Vitamin B2
C) Vitamin B3
D) Vitamin B12
Answer: A) Vitamin B1
Rationale: Thiamine (B1) deficiency causes beriberi, affecting the
cardiovascular and nervous systems.
5. A patient has prolonged bleeding time but normal PT and aPTT.
Which factor is most likely defective?
A) Factor VIII
B) Platelets
C) Factor VII
D) Factor IX
Answer: B) Platelets
Rationale: Prolonged bleeding time with normal PT and aPTT
indicates a platelet defect, not a coagulation factor deficiency.
,6. Which neurotransmitter is primarily deficient in Parkinson’s
disease?
A) Acetylcholine
B) Dopamine
C) Serotonin
D) GABA
Answer: B) Dopamine
Rationale: Parkinson’s disease is characterized by degeneration of
dopaminergic neurons in the substantia nigra.
7. A patient with a high fever, cough, and rusty-colored sputum most
likely has:
A) Mycoplasma pneumonia
B) Pneumococcal pneumonia
C) Klebsiella pneumonia
D) Legionella pneumonia
Answer: B) Pneumococcal pneumonia
Rationale: Streptococcus pneumoniae is the most common cause of
community-acquired pneumonia and produces rusty sputum.
8. A 45-year-old man presents with jaundice, dark urine, and pale
stools. Which lab pattern is most consistent with obstructive
jaundice?
A) High unconjugated bilirubin
B) High conjugated bilirubin, elevated ALP
C) Low total bilirubin
D) High AST/ALT only
Answer: B) High conjugated bilirubin, elevated ALP
Rationale: Obstruction causes conjugated hyperbilirubinemia and
cholestatic enzymes (ALP, GGT) elevation.
, 9. Which type of hypersensitivity is mediated by IgE?
A) Type I
B) Type II
C) Type III
D) Type IV
Answer: A) Type I
Rationale: Type I hypersensitivity reactions involve IgE-mediated
mast cell degranulation (e.g., anaphylaxis, allergies).
10. Which structure forms the blood-brain barrier?
A) Astrocyte end-feet
B) Microglia
C) Neuronal cell bodies
D) Ependymal cells
Answer: A) Astrocyte end-feet
Rationale: Astrocytes contribute to the tight junctions of endothelial
cells, forming the blood-brain barrier.
11. Which cell type is primarily responsible for humoral immunity?
A) T cells
B) B cells
C) NK cells
D) Macrophages
Answer: B) B cells
Rationale: B cells differentiate into plasma cells that produce
antibodies, mediating humoral immunity.
