Comprehensive Osteopathic Medical
Licensing Examination (COMLEX) Level 1
— 100-Question Practice Exam with
Answers and Rationales
1. A 6-year-old boy presents with recurrent sinopulmonary infections and
absent tonsils. Laboratory studies show very low B cells and markedly
decreased immunoglobulins of all isotypes. Which of the following is the
most likely diagnosis?
A. Selective IgA deficiency
B. X-linked agammaglobulinemia
C. Common variable immunodeficiency
D. Hyper-IgM syndrome
Answer: B. X-linked agammaglobulinemia
Rationale: Bruton's (X-linked) agammaglobulinemia presents in boys with
absent/malformed tonsils, low B cells, and very low Ig due to B-cell
maturation defect (BTK mutation).
2. A 55-year-old man with long-standing hypertension develops concentric
left ventricular hypertrophy. Which physiological change best explains his
increased myocardial wall thickness?
A. Increased sarcomere addition in series
B. Increased sarcomere addition in parallel
C. Increased myocardial apoptosis
D. Increased chamber dilation
Answer: B. Increased sarcomere addition in parallel
, Rationale: Pressure overload leads to concentric hypertrophy via
sarcomeres added in parallel, increasing wall thickness.
3. A patient has severe hypokalemia due to diuretic use. Which EKG change is
most likely?
A. Peaked T waves
B. Prolonged PR interval
C. U waves and flattened T waves
D. Widened QRS complex
Answer: C. U waves and flattened T waves
Rationale: Hypokalemia commonly causes U waves and flattened T waves
on ECG; peaked T waves are seen in hyperkalemia.
4. A 25-year-old woman has painful menses and imaging shows
endometriosis. Which tissue is most commonly involved in endometriosis?
A. Ovaries
B. Cervix
C. Fallopian tubes
D. Vagina
Answer: A. Ovaries
Rationale: The ovaries are a common site of endometriosis, often forming
"chocolate" cysts (endometriomas).
5. A 40-year-old diabetic patient develops a nonhealing foot ulcer infected
with Pseudomonas. Which antibiotic is most appropriate for Pseudomonas
coverage?
A. Vancomycin
B. Cefazolin
C. Piperacillin-tazobactam
D. Metronidazole
Answer: C. Piperacillin-tazobactam
Rationale: Piperacillin-tazobactam provides broad gram-negative
including Pseudomonas coverage; vancomycin covers MRSA but not
Pseudomonas.
, 6. Which enzyme deficiency in glycolysis leads to hemolytic anemia due to
decreased ATP in red blood cells?
A. Hexokinase
B. Pyruvate kinase
C. Phosphofructokinase-1
D. Lactate dehydrogenase
Answer: B. Pyruvate kinase
Rationale: Pyruvate kinase deficiency reduces ATP production in RBCs
causing hemolysis; it's a common glycolytic enzyme defect producing
chronic hemolytic anemia.
7. A patient with nephrotic syndrome has hyperlipidemia. The hyperlipidemia
is primarily due to:
A. Increased LDL receptor activity
B. Increased hepatic lipoprotein synthesis
C. Decreased lipoprotein synthesis
D. Increased peripheral lipoprotein lipase activity
Answer: B. Increased hepatic lipoprotein synthesis
Rationale: Hypoalbuminemia stimulates hepatic synthesis of lipoproteins,
causing hyperlipidemia in nephrotic syndrome.
8. A newborn fails the hearing screen. The otoscopic exam is normal. Which
test most directly evaluates cochlear (sensory) hearing loss?
A. Tympanometry
B. Auditory brainstem response (ABR)
C. Rinne and Weber tests
D. Otoacoustic emissions (OAEs)
Answer: D. Otoacoustic emissions (OAEs)
Rationale: OAEs assess outer hair cell (cochlear) function; absent OAEs
suggest sensorineural (cochlear) hearing loss.
9. Which vessel is most commonly injured in a posterior-inferior myocardial
infarction?
A. Left anterior descending artery
Licensing Examination (COMLEX) Level 1
— 100-Question Practice Exam with
Answers and Rationales
1. A 6-year-old boy presents with recurrent sinopulmonary infections and
absent tonsils. Laboratory studies show very low B cells and markedly
decreased immunoglobulins of all isotypes. Which of the following is the
most likely diagnosis?
A. Selective IgA deficiency
B. X-linked agammaglobulinemia
C. Common variable immunodeficiency
D. Hyper-IgM syndrome
Answer: B. X-linked agammaglobulinemia
Rationale: Bruton's (X-linked) agammaglobulinemia presents in boys with
absent/malformed tonsils, low B cells, and very low Ig due to B-cell
maturation defect (BTK mutation).
2. A 55-year-old man with long-standing hypertension develops concentric
left ventricular hypertrophy. Which physiological change best explains his
increased myocardial wall thickness?
A. Increased sarcomere addition in series
B. Increased sarcomere addition in parallel
C. Increased myocardial apoptosis
D. Increased chamber dilation
Answer: B. Increased sarcomere addition in parallel
, Rationale: Pressure overload leads to concentric hypertrophy via
sarcomeres added in parallel, increasing wall thickness.
3. A patient has severe hypokalemia due to diuretic use. Which EKG change is
most likely?
A. Peaked T waves
B. Prolonged PR interval
C. U waves and flattened T waves
D. Widened QRS complex
Answer: C. U waves and flattened T waves
Rationale: Hypokalemia commonly causes U waves and flattened T waves
on ECG; peaked T waves are seen in hyperkalemia.
4. A 25-year-old woman has painful menses and imaging shows
endometriosis. Which tissue is most commonly involved in endometriosis?
A. Ovaries
B. Cervix
C. Fallopian tubes
D. Vagina
Answer: A. Ovaries
Rationale: The ovaries are a common site of endometriosis, often forming
"chocolate" cysts (endometriomas).
5. A 40-year-old diabetic patient develops a nonhealing foot ulcer infected
with Pseudomonas. Which antibiotic is most appropriate for Pseudomonas
coverage?
A. Vancomycin
B. Cefazolin
C. Piperacillin-tazobactam
D. Metronidazole
Answer: C. Piperacillin-tazobactam
Rationale: Piperacillin-tazobactam provides broad gram-negative
including Pseudomonas coverage; vancomycin covers MRSA but not
Pseudomonas.
, 6. Which enzyme deficiency in glycolysis leads to hemolytic anemia due to
decreased ATP in red blood cells?
A. Hexokinase
B. Pyruvate kinase
C. Phosphofructokinase-1
D. Lactate dehydrogenase
Answer: B. Pyruvate kinase
Rationale: Pyruvate kinase deficiency reduces ATP production in RBCs
causing hemolysis; it's a common glycolytic enzyme defect producing
chronic hemolytic anemia.
7. A patient with nephrotic syndrome has hyperlipidemia. The hyperlipidemia
is primarily due to:
A. Increased LDL receptor activity
B. Increased hepatic lipoprotein synthesis
C. Decreased lipoprotein synthesis
D. Increased peripheral lipoprotein lipase activity
Answer: B. Increased hepatic lipoprotein synthesis
Rationale: Hypoalbuminemia stimulates hepatic synthesis of lipoproteins,
causing hyperlipidemia in nephrotic syndrome.
8. A newborn fails the hearing screen. The otoscopic exam is normal. Which
test most directly evaluates cochlear (sensory) hearing loss?
A. Tympanometry
B. Auditory brainstem response (ABR)
C. Rinne and Weber tests
D. Otoacoustic emissions (OAEs)
Answer: D. Otoacoustic emissions (OAEs)
Rationale: OAEs assess outer hair cell (cochlear) function; absent OAEs
suggest sensorineural (cochlear) hearing loss.
9. Which vessel is most commonly injured in a posterior-inferior myocardial
infarction?
A. Left anterior descending artery
