LATEST USMLE STEP 1 PRACTICE EXAM QUESTIONS
AND ANSWERS WITH DUMP PDF.
1. A 65-year-old man presents with progressive dyspnea. Histology shows enlarged
alveolar spaces with destruction of septa. Which mechanism best explains this
finding?
A. Increased surfactant production
B. Protease-antiprotease imbalance
C. Decreased collagen synthesis
D. Autoimmune alveolar destruction
Correct Answer: B
Rationale: Emphysema is caused by a protease-antiprotease imbalance leading to
destruction of alveolar walls. Increased surfactant and decreased collagen are not
primary mechanisms, and autoimmune destruction is not typical.
2. A patient with chronic alcoholism presents with confusion and ophthalmoplegia.
Which vitamin deficiency is most likely?
A. Vitamin B1
B. Vitamin B6
C. Vitamin B12
D. Vitamin C
Correct Answer: A
Rationale: Thiamine (B1) deficiency causes Wernicke encephalopathy. B6 causes
neuropathy, B12 causes megaloblastic anemia, and vitamin C causes scurvy.
3. A 25-year-old woman presents with fatigue. Labs show Hb 8 g/dL, MCV 70 fL. What
is the most likely diagnosis?
A. Iron deficiency anemia
B. Aplastic anemia
C. Hemolytic anemia
D. Pernicious anemia
Correct Answer: A
Rationale: Microcytic anemia (low MCV) is most commonly due to iron deficiency.
Aplastic anemia affects all cell lines, hemolytic anemia is normocytic, and pernicious
anemia is macrocytic.
4. A newborn presents with vomiting and lethargy. Elevated ammonia levels are noted.
Which pathway is defective?
A. Glycolysis
B. Urea cycle
C. TCA cycle
, D. Pentose phosphate pathway
Correct Answer: B
Rationale: Hyperammonemia in newborns suggests a urea cycle defect. Other
pathways do not primarily regulate ammonia detoxification.
5. A drug inhibits bacterial cell wall synthesis by binding penicillin-binding proteins.
Which drug class is this?
A. Macrolides
B. Beta-lactams
C. Aminoglycosides
D. Tetracyclines
Correct Answer: B
Rationale: Beta-lactams inhibit PBPs and prevent cell wall synthesis. Others act on
ribosomes.
6. A patient develops flushing and diarrhea due to excess serotonin. Which tumor is
most likely?
A. Insulinoma
B. Carcinoid tumor
C. Gastrinoma
D. Pheochromocytoma
Correct Answer: B
Rationale: Carcinoid tumors secrete serotonin causing flushing and diarrhea. Others
produce different hormones.
7. A 40-year-old woman has exophthalmos and heat intolerance. Which antibody is
responsible?
A. Anti-thyroglobulin
B. Anti-TPO
C. TSH receptor stimulating antibody
D. Anti-TSH
Correct Answer: C
Rationale: Graves disease is caused by TSH receptor-stimulating antibodies. Others
are seen in Hashimoto or are not pathogenic.
8. A patient presents with hypercalcemia and low phosphate. Which hormone is
elevated?
A. Calcitonin
B. Vitamin D
C. Parathyroid hormone
D. Cortisol
Correct Answer: C
, Rationale: PTH increases calcium and decreases phosphate. Calcitonin lowers
calcium, vitamin D increases both, cortisol has minimal direct effect.
9. A mutation in which gene is associated with familial hypercholesterolemia?
A. LDL receptor
B. ApoA1
C. HMG-CoA reductase
D. Lipoprotein lipase
Correct Answer: A
Rationale: LDL receptor mutations cause increased LDL levels. Others are not
primary causes.
10. A patient has a lesion in the left temporal lobe. Which deficit is expected?
A. Right hemiparesis
B. Aphasia
C. Loss of vision
D. Ataxia
Correct Answer: B
Rationale: Temporal lobe lesions affect language (Wernicke area). Motor deficits are
frontal, vision occipital, ataxia cerebellar.
11. Which enzyme converts angiotensin I to angiotensin II?
A. Renin
B. ACE
C. Aldosterone
D. ADH
Correct Answer: B
Rationale: ACE converts angiotensin I to II. Renin produces angiotensin I.
12. A patient with HIV has CD4 count of 150. Which infection is most likely?
A. Pneumocystis jirovecii
B. Candida
C. CMV
D. Mycobacterium tuberculosis
Correct Answer: A
Rationale: PCP occurs when CD4 <200. CMV occurs at lower levels.
13. A 50-year-old smoker has hematuria. Which cancer is most likely?
A. Renal cell carcinoma
B. Bladder carcinoma
, C. Prostate cancer
D. Testicular cancer
Correct Answer: B
Rationale: Smoking is strongly associated with bladder cancer presenting as painless
hematuria.
14. Which neurotransmitter is decreased in Parkinson disease?
A. Serotonin
B. Dopamine
C. GABA
D. Glutamate
Correct Answer: B
Rationale: Parkinson disease involves loss of dopaminergic neurons in substantia
nigra.
15. A patient presents with metabolic acidosis and increased anion gap. Which condition
is likely?
A. Diarrhea
B. Lactic acidosis
C. Renal tubular acidosis
D. Vomiting
Correct Answer: B
Rationale: Lactic acidosis causes high anion gap acidosis. Diarrhea causes normal
gap acidosis.
16. Which structure produces cerebrospinal fluid?
A. Arachnoid granulations
B. Choroid plexus
C. Pia mater
D. Dura mater
Correct Answer: B
Rationale: CSF is produced by the choroid plexus.
17. A deficiency of which factor causes hemophilia A?
A. Factor VIII
B. Factor IX
C. Factor V
D. Factor X
Correct Answer: A
Rationale: Hemophilia A is due to factor VIII deficiency. Factor IX causes hemophilia
B.
AND ANSWERS WITH DUMP PDF.
1. A 65-year-old man presents with progressive dyspnea. Histology shows enlarged
alveolar spaces with destruction of septa. Which mechanism best explains this
finding?
A. Increased surfactant production
B. Protease-antiprotease imbalance
C. Decreased collagen synthesis
D. Autoimmune alveolar destruction
Correct Answer: B
Rationale: Emphysema is caused by a protease-antiprotease imbalance leading to
destruction of alveolar walls. Increased surfactant and decreased collagen are not
primary mechanisms, and autoimmune destruction is not typical.
2. A patient with chronic alcoholism presents with confusion and ophthalmoplegia.
Which vitamin deficiency is most likely?
A. Vitamin B1
B. Vitamin B6
C. Vitamin B12
D. Vitamin C
Correct Answer: A
Rationale: Thiamine (B1) deficiency causes Wernicke encephalopathy. B6 causes
neuropathy, B12 causes megaloblastic anemia, and vitamin C causes scurvy.
3. A 25-year-old woman presents with fatigue. Labs show Hb 8 g/dL, MCV 70 fL. What
is the most likely diagnosis?
A. Iron deficiency anemia
B. Aplastic anemia
C. Hemolytic anemia
D. Pernicious anemia
Correct Answer: A
Rationale: Microcytic anemia (low MCV) is most commonly due to iron deficiency.
Aplastic anemia affects all cell lines, hemolytic anemia is normocytic, and pernicious
anemia is macrocytic.
4. A newborn presents with vomiting and lethargy. Elevated ammonia levels are noted.
Which pathway is defective?
A. Glycolysis
B. Urea cycle
C. TCA cycle
, D. Pentose phosphate pathway
Correct Answer: B
Rationale: Hyperammonemia in newborns suggests a urea cycle defect. Other
pathways do not primarily regulate ammonia detoxification.
5. A drug inhibits bacterial cell wall synthesis by binding penicillin-binding proteins.
Which drug class is this?
A. Macrolides
B. Beta-lactams
C. Aminoglycosides
D. Tetracyclines
Correct Answer: B
Rationale: Beta-lactams inhibit PBPs and prevent cell wall synthesis. Others act on
ribosomes.
6. A patient develops flushing and diarrhea due to excess serotonin. Which tumor is
most likely?
A. Insulinoma
B. Carcinoid tumor
C. Gastrinoma
D. Pheochromocytoma
Correct Answer: B
Rationale: Carcinoid tumors secrete serotonin causing flushing and diarrhea. Others
produce different hormones.
7. A 40-year-old woman has exophthalmos and heat intolerance. Which antibody is
responsible?
A. Anti-thyroglobulin
B. Anti-TPO
C. TSH receptor stimulating antibody
D. Anti-TSH
Correct Answer: C
Rationale: Graves disease is caused by TSH receptor-stimulating antibodies. Others
are seen in Hashimoto or are not pathogenic.
8. A patient presents with hypercalcemia and low phosphate. Which hormone is
elevated?
A. Calcitonin
B. Vitamin D
C. Parathyroid hormone
D. Cortisol
Correct Answer: C
, Rationale: PTH increases calcium and decreases phosphate. Calcitonin lowers
calcium, vitamin D increases both, cortisol has minimal direct effect.
9. A mutation in which gene is associated with familial hypercholesterolemia?
A. LDL receptor
B. ApoA1
C. HMG-CoA reductase
D. Lipoprotein lipase
Correct Answer: A
Rationale: LDL receptor mutations cause increased LDL levels. Others are not
primary causes.
10. A patient has a lesion in the left temporal lobe. Which deficit is expected?
A. Right hemiparesis
B. Aphasia
C. Loss of vision
D. Ataxia
Correct Answer: B
Rationale: Temporal lobe lesions affect language (Wernicke area). Motor deficits are
frontal, vision occipital, ataxia cerebellar.
11. Which enzyme converts angiotensin I to angiotensin II?
A. Renin
B. ACE
C. Aldosterone
D. ADH
Correct Answer: B
Rationale: ACE converts angiotensin I to II. Renin produces angiotensin I.
12. A patient with HIV has CD4 count of 150. Which infection is most likely?
A. Pneumocystis jirovecii
B. Candida
C. CMV
D. Mycobacterium tuberculosis
Correct Answer: A
Rationale: PCP occurs when CD4 <200. CMV occurs at lower levels.
13. A 50-year-old smoker has hematuria. Which cancer is most likely?
A. Renal cell carcinoma
B. Bladder carcinoma
, C. Prostate cancer
D. Testicular cancer
Correct Answer: B
Rationale: Smoking is strongly associated with bladder cancer presenting as painless
hematuria.
14. Which neurotransmitter is decreased in Parkinson disease?
A. Serotonin
B. Dopamine
C. GABA
D. Glutamate
Correct Answer: B
Rationale: Parkinson disease involves loss of dopaminergic neurons in substantia
nigra.
15. A patient presents with metabolic acidosis and increased anion gap. Which condition
is likely?
A. Diarrhea
B. Lactic acidosis
C. Renal tubular acidosis
D. Vomiting
Correct Answer: B
Rationale: Lactic acidosis causes high anion gap acidosis. Diarrhea causes normal
gap acidosis.
16. Which structure produces cerebrospinal fluid?
A. Arachnoid granulations
B. Choroid plexus
C. Pia mater
D. Dura mater
Correct Answer: B
Rationale: CSF is produced by the choroid plexus.
17. A deficiency of which factor causes hemophilia A?
A. Factor VIII
B. Factor IX
C. Factor V
D. Factor X
Correct Answer: A
Rationale: Hemophilia A is due to factor VIII deficiency. Factor IX causes hemophilia
B.
