NBME CBSE Practice Exam 2026–2027: 250 Original
Questions with Answers & Detailed Explanations | USMLE
Step 1 High-Yield Review
Questions 1–50
1.
A 23-year-old woman presents with fatigue, weight loss, and heat intolerance. She has a
fine tremor and diffuse thyroid enlargement. Laboratory studies show increased free T4 and
suppressed TSH. Which mechanism most directly explains her condition?
A. Antibodies stimulating the TSH receptor
B. Antibodies destroying thyroid follicular cells
C. Increased iodine uptake caused by TSH
D. Autonomous secretion of TSH by the pituitary
Answer: A. Antibodies stimulating the TSH receptor
Graves disease results from IgG antibodies that stimulate the TSH receptor, causing
increased thyroid hormone synthesis and diffuse thyroid enlargement. Hashimoto thyroiditis
involves autoimmune destruction, whereas pituitary TSH secretion would not produce a
suppressed TSH.
2.
,A 65-year-old man develops sudden weakness of the right face and right arm. He also has
expressive aphasia. Which vascular territory is most likely affected?
A. Right middle cerebral artery
B. Left middle cerebral artery
C. Right posterior cerebral artery
D. Left posterior cerebral artery
Answer: B. Left middle cerebral artery
The dominant hemisphere is usually the left hemisphere. A dominant MCA lesion can cause
contralateral face/arm weakness and expressive aphasia when Broca area is involved.
3.
A newborn develops severe respiratory distress shortly after birth. The infant was born at 29
weeks' gestation. Deficiency of which substance is primarily responsible?
A. Fetal hemoglobin
B. Surfactant
C. Elastin
D. Prostaglandin E2
Answer: B. Surfactant
Premature infants are at risk for neonatal respiratory distress syndrome because type II
pneumocytes have insufficient surfactant production. Surfactant decreases alveolar surface
tension and prevents collapse.
,4.
A patient taking an antibiotic develops hemolytic anemia, jaundice, and dark urine after
exposure to oxidant stress. Which enzyme deficiency is most likely?
A. Pyruvate kinase
B. Glucose-6-phosphate dehydrogenase
C. Hexokinase
D. Lactate dehydrogenase
Answer: B. Glucose-6-phosphate dehydrogenase
G6PD generates NADPH, which maintains glutathione in its reduced form. Deficiency
makes RBCs vulnerable to oxidative injury, producing Heinz bodies and bite cells.
5.
A 58-year-old man has crushing substernal chest pain. ECG shows ST elevations in leads
II, III, and aVF. Which coronary artery is most likely occluded?
A. Left anterior descending artery
B. Left circumflex artery
C. Right coronary artery
D. Left main coronary artery
Answer: C. Right coronary artery
, An inferior-wall myocardial infarction is classically associated with right coronary artery
occlusion. The RCA commonly supplies the inferior wall and AV node.
6.
A patient with chronic cough, fever, night sweats, and weight loss has an upper-lobe
cavitary lesion. Which immune mechanism is most important in containing the infection?
A. IgE-mediated mast-cell activation
B. CD8+ cytotoxicity alone
C. Th1 activation of macrophages
D. Complement-mediated lysis
Answer: C. Th1 activation of macrophages
Mycobacterium tuberculosis is controlled primarily through cell-mediated immunity. Th1
cells produce IFN-γ, which activates macrophages and promotes granuloma formation.
7.
A 42-year-old woman has recurrent kidney stones, bone pain, and constipation. Serum
calcium and PTH are elevated. Which additional finding is most likely?
A. Decreased urinary phosphate
B. Increased serum phosphate
C. Increased renal phosphate reabsorption
D. Decreased urinary cAMP
Questions with Answers & Detailed Explanations | USMLE
Step 1 High-Yield Review
Questions 1–50
1.
A 23-year-old woman presents with fatigue, weight loss, and heat intolerance. She has a
fine tremor and diffuse thyroid enlargement. Laboratory studies show increased free T4 and
suppressed TSH. Which mechanism most directly explains her condition?
A. Antibodies stimulating the TSH receptor
B. Antibodies destroying thyroid follicular cells
C. Increased iodine uptake caused by TSH
D. Autonomous secretion of TSH by the pituitary
Answer: A. Antibodies stimulating the TSH receptor
Graves disease results from IgG antibodies that stimulate the TSH receptor, causing
increased thyroid hormone synthesis and diffuse thyroid enlargement. Hashimoto thyroiditis
involves autoimmune destruction, whereas pituitary TSH secretion would not produce a
suppressed TSH.
2.
,A 65-year-old man develops sudden weakness of the right face and right arm. He also has
expressive aphasia. Which vascular territory is most likely affected?
A. Right middle cerebral artery
B. Left middle cerebral artery
C. Right posterior cerebral artery
D. Left posterior cerebral artery
Answer: B. Left middle cerebral artery
The dominant hemisphere is usually the left hemisphere. A dominant MCA lesion can cause
contralateral face/arm weakness and expressive aphasia when Broca area is involved.
3.
A newborn develops severe respiratory distress shortly after birth. The infant was born at 29
weeks' gestation. Deficiency of which substance is primarily responsible?
A. Fetal hemoglobin
B. Surfactant
C. Elastin
D. Prostaglandin E2
Answer: B. Surfactant
Premature infants are at risk for neonatal respiratory distress syndrome because type II
pneumocytes have insufficient surfactant production. Surfactant decreases alveolar surface
tension and prevents collapse.
,4.
A patient taking an antibiotic develops hemolytic anemia, jaundice, and dark urine after
exposure to oxidant stress. Which enzyme deficiency is most likely?
A. Pyruvate kinase
B. Glucose-6-phosphate dehydrogenase
C. Hexokinase
D. Lactate dehydrogenase
Answer: B. Glucose-6-phosphate dehydrogenase
G6PD generates NADPH, which maintains glutathione in its reduced form. Deficiency
makes RBCs vulnerable to oxidative injury, producing Heinz bodies and bite cells.
5.
A 58-year-old man has crushing substernal chest pain. ECG shows ST elevations in leads
II, III, and aVF. Which coronary artery is most likely occluded?
A. Left anterior descending artery
B. Left circumflex artery
C. Right coronary artery
D. Left main coronary artery
Answer: C. Right coronary artery
, An inferior-wall myocardial infarction is classically associated with right coronary artery
occlusion. The RCA commonly supplies the inferior wall and AV node.
6.
A patient with chronic cough, fever, night sweats, and weight loss has an upper-lobe
cavitary lesion. Which immune mechanism is most important in containing the infection?
A. IgE-mediated mast-cell activation
B. CD8+ cytotoxicity alone
C. Th1 activation of macrophages
D. Complement-mediated lysis
Answer: C. Th1 activation of macrophages
Mycobacterium tuberculosis is controlled primarily through cell-mediated immunity. Th1
cells produce IFN-γ, which activates macrophages and promotes granuloma formation.
7.
A 42-year-old woman has recurrent kidney stones, bone pain, and constipation. Serum
calcium and PTH are elevated. Which additional finding is most likely?
A. Decreased urinary phosphate
B. Increased serum phosphate
C. Increased renal phosphate reabsorption
D. Decreased urinary cAMP
