NBME BASIC SCIENCE EXAM LATEST 2026 UPDATE
100+ QUESTIONS AND DETAILED VERIFIED
ANSWERS FROM ACTUAL EXAMS TEST GRADE A+
Question 1
A 45-year-old man presents with fatigue, weight loss, and a darkening of his skin.
Lab tests show hyponatremia, hyperkalemia, and low cortisol. Which layer of the
adrenal cortex is primarily affected?
A) Zona glomerulosa
B) Zona fasciculata
C) Zona reticularis
D) Adrenal medulla
Correct Answer: A
Explanation: The zona glomerulosa produces mineralocorticoids (aldosterone).
Destruction here causes hypoaldosteronism → hyponatremia, hyperkalemia. The
symptoms also involve cortisol deficiency (zona fasciculata), but the electrolyte
changes point to glomerulosa damage.
Question 2
A 60-year-old with chronic hepatitis C develops ascites and esophageal varices.
Which laboratory finding is most consistent with liver failure?
A) Elevated serum albumin
B) Prolonged PT/INR
C) Elevated serum iron
D) Decreased ammonia
Correct Answer: B
Explanation: The liver synthesizes clotting factors; in failure, PT/INR prolongs.
,Albumin decreases (not increases), ammonia increases, and iron is not directly
related to synthetic failure.
Question 3
A 30-year-old woman presents with episodic headaches, palpitations, and
diaphoresis. Her blood pressure is 180/110 mmHg. A 24-hour urine shows
elevated metanephrines. Where is the most likely tumor location?
A) Adrenal cortex
B) Adrenal medulla
C) Thyroid
D) Pituitary
Correct Answer: B
Explanation: Elevated metanephrines indicate a pheochromocytoma, a tumor of
the adrenal medulla (chromaffin cells). It causes episodic hypertension, headache,
and diaphoresis.
Question 4
A 55-year-old with a 30-pack-year smoking history presents with hemoptysis and
weight loss. Chest CT shows a 4 cm central lung mass. Biopsy reveals small cells
with scant cytoplasm and nuclear molding. Which paraneoplastic syndrome is
most likely?
A) Hypercalcemia
B) SIADH
C) Acromegaly
D) Cushing's syndrome due to ACTH
Correct Answer: B
Explanation: Small cell lung cancer often secretes ADH causing SIADH
(hyponatremia). Hypercalcemia is more common with squamous cell; ACTH excess
also occurs but SIADH is most frequent.
,Question 5
A 70-year-old man has a sudden onset of right-sided hemiplegia and aphasia. CT
shows no hemorrhage. An ECG reveals atrial fibrillation. What is the most likely
mechanism of stroke?
A) Thrombotic occlusion of the middle cerebral artery
B) Embolic occlusion from a cardiac source
C) Lacunar infarct due to hypertension
D) Vasospasm after subarachnoid hemorrhage
Correct Answer: B
Explanation: Atrial fibrillation predisposes to left atrial thrombi, which embolize to
the brain. This is an embolic stroke, not thrombotic (no atherosclerosis history
given) or lacunar (hypertensive small vessel disease).
Question 6
A 25-year-old college student has fever, sore throat, and lymphadenopathy. A
Monospot test is positive. Which cell is primarily infected by the causative virus?
A) CD4+ T cells
B) CD8+ T cells
C) B cells
D) Macrophages
Correct Answer: C
*Explanation: Epstein-Barr virus (infectious mononucleosis) infects B cells via
CD21 receptor. The atypical lymphocytes seen are activated CD8+ T cells
responding to infected B cells.*
Question 7
A 50-year-old with alcoholism presents with nystagmus, ataxia, and confusion.
Thiamine is administered. Which enzyme is most directly affected by thiamine
deficiency?
A) Pyruvate dehydrogenase
, B) Succinate dehydrogenase
C) Malate dehydrogenase
D) Glucose-6-phosphatase
Correct Answer: A
Explanation: Thiamine pyrophosphate is a cofactor for pyruvate dehydrogenase,
alpha-ketoglutarate dehydrogenase, and transketolase. Deficiency impairs
pyruvate metabolism, leading to Wernicke encephalopathy.
Question 8
A 72-year-old with Parkinson's disease has been on levodopa/carbidopa for 5
years. He now has jerky, involuntary movements of his face and limbs. What is the
most likely cause?
A) Tardive dyskinesia
B) Levodopa-induced dyskinesia
C) Worsening Parkinson's
D) Neuroleptic malignant syndrome
Correct Answer: B
Explanation: Long-term levodopa use causes dyskinesias (choreoathetoid
movements) due to pulsatile stimulation of dopamine receptors. Tardive dyskinesia
is from antipsychotics, not levodopa.
Question 9
A 2-day-old neonate has projectile vomiting after feeds. Physical exam shows a
palpable olive-shaped mass in the right upper quadrant. What is the diagnosis?
A) Pyloric stenosis
B) Malrotation with volvulus
C) Intussusception
D) Hirschsprung disease
Correct Answer: A
*Explanation: Hypertrophic pyloric stenosis presents at 2-6 weeks with projectile
100+ QUESTIONS AND DETAILED VERIFIED
ANSWERS FROM ACTUAL EXAMS TEST GRADE A+
Question 1
A 45-year-old man presents with fatigue, weight loss, and a darkening of his skin.
Lab tests show hyponatremia, hyperkalemia, and low cortisol. Which layer of the
adrenal cortex is primarily affected?
A) Zona glomerulosa
B) Zona fasciculata
C) Zona reticularis
D) Adrenal medulla
Correct Answer: A
Explanation: The zona glomerulosa produces mineralocorticoids (aldosterone).
Destruction here causes hypoaldosteronism → hyponatremia, hyperkalemia. The
symptoms also involve cortisol deficiency (zona fasciculata), but the electrolyte
changes point to glomerulosa damage.
Question 2
A 60-year-old with chronic hepatitis C develops ascites and esophageal varices.
Which laboratory finding is most consistent with liver failure?
A) Elevated serum albumin
B) Prolonged PT/INR
C) Elevated serum iron
D) Decreased ammonia
Correct Answer: B
Explanation: The liver synthesizes clotting factors; in failure, PT/INR prolongs.
,Albumin decreases (not increases), ammonia increases, and iron is not directly
related to synthetic failure.
Question 3
A 30-year-old woman presents with episodic headaches, palpitations, and
diaphoresis. Her blood pressure is 180/110 mmHg. A 24-hour urine shows
elevated metanephrines. Where is the most likely tumor location?
A) Adrenal cortex
B) Adrenal medulla
C) Thyroid
D) Pituitary
Correct Answer: B
Explanation: Elevated metanephrines indicate a pheochromocytoma, a tumor of
the adrenal medulla (chromaffin cells). It causes episodic hypertension, headache,
and diaphoresis.
Question 4
A 55-year-old with a 30-pack-year smoking history presents with hemoptysis and
weight loss. Chest CT shows a 4 cm central lung mass. Biopsy reveals small cells
with scant cytoplasm and nuclear molding. Which paraneoplastic syndrome is
most likely?
A) Hypercalcemia
B) SIADH
C) Acromegaly
D) Cushing's syndrome due to ACTH
Correct Answer: B
Explanation: Small cell lung cancer often secretes ADH causing SIADH
(hyponatremia). Hypercalcemia is more common with squamous cell; ACTH excess
also occurs but SIADH is most frequent.
,Question 5
A 70-year-old man has a sudden onset of right-sided hemiplegia and aphasia. CT
shows no hemorrhage. An ECG reveals atrial fibrillation. What is the most likely
mechanism of stroke?
A) Thrombotic occlusion of the middle cerebral artery
B) Embolic occlusion from a cardiac source
C) Lacunar infarct due to hypertension
D) Vasospasm after subarachnoid hemorrhage
Correct Answer: B
Explanation: Atrial fibrillation predisposes to left atrial thrombi, which embolize to
the brain. This is an embolic stroke, not thrombotic (no atherosclerosis history
given) or lacunar (hypertensive small vessel disease).
Question 6
A 25-year-old college student has fever, sore throat, and lymphadenopathy. A
Monospot test is positive. Which cell is primarily infected by the causative virus?
A) CD4+ T cells
B) CD8+ T cells
C) B cells
D) Macrophages
Correct Answer: C
*Explanation: Epstein-Barr virus (infectious mononucleosis) infects B cells via
CD21 receptor. The atypical lymphocytes seen are activated CD8+ T cells
responding to infected B cells.*
Question 7
A 50-year-old with alcoholism presents with nystagmus, ataxia, and confusion.
Thiamine is administered. Which enzyme is most directly affected by thiamine
deficiency?
A) Pyruvate dehydrogenase
, B) Succinate dehydrogenase
C) Malate dehydrogenase
D) Glucose-6-phosphatase
Correct Answer: A
Explanation: Thiamine pyrophosphate is a cofactor for pyruvate dehydrogenase,
alpha-ketoglutarate dehydrogenase, and transketolase. Deficiency impairs
pyruvate metabolism, leading to Wernicke encephalopathy.
Question 8
A 72-year-old with Parkinson's disease has been on levodopa/carbidopa for 5
years. He now has jerky, involuntary movements of his face and limbs. What is the
most likely cause?
A) Tardive dyskinesia
B) Levodopa-induced dyskinesia
C) Worsening Parkinson's
D) Neuroleptic malignant syndrome
Correct Answer: B
Explanation: Long-term levodopa use causes dyskinesias (choreoathetoid
movements) due to pulsatile stimulation of dopamine receptors. Tardive dyskinesia
is from antipsychotics, not levodopa.
Question 9
A 2-day-old neonate has projectile vomiting after feeds. Physical exam shows a
palpable olive-shaped mass in the right upper quadrant. What is the diagnosis?
A) Pyloric stenosis
B) Malrotation with volvulus
C) Intussusception
D) Hirschsprung disease
Correct Answer: A
*Explanation: Hypertrophic pyloric stenosis presents at 2-6 weeks with projectile
