COMSAE Phase 1 Practice Exam questions
and answers with rationales 2025-2026
Master COMSAE Phase 1 using 100 original board-style practice questions, detailed rationales, and
high-yield explanations for comprehensive COMLEX-USA preparation.
1.
A 19-year-old college student presents with fever, headache, neck stiffness, and a petechial rash.
Cerebrospinal fluid analysis reveals elevated protein, decreased glucose, and neutrophilic
pleocytosis. Which organism is the most likely cause?
A. Streptococcus pneumoniae
B. Neisseria meningitidis
C. Listeria monocytogenes
D. Haemophilus influenzae
E. Cryptococcus neoformans
Answer: B
Rationale: Neisseria meningitidis commonly causes bacterial meningitis in adolescents and young
adults. Petechial rash, meningitis, and rapid progression to septic shock are classic features.*
2.
A patient presents with muscle weakness that improves with repeated use. Autoantibodies are
directed against presynaptic voltage-gated calcium channels. Which disorder is most likely?
A. Myasthenia gravis
B. Lambert-Eaton myasthenic syndrome
C. Multiple sclerosis
D. Guillain-Barré syndrome
E. Amyotrophic lateral sclerosis
Answer: B
Rationale: Lambert-Eaton syndrome results from antibodies against presynaptic calcium channels,
reducing acetylcholine release. Unlike myasthenia gravis, strength often improves with repeated
muscle use.*
3.
A patient has elevated serum calcium and decreased serum phosphate due to excessive secretion of
parathyroid hormone. Which renal enzyme activity is increased?
A. Carbonic anhydrase
B. Renin
C. 1-alpha-hydroxylase
,D. Xanthine oxidase
E. ACE
Answer: C
Rationale: Parathyroid hormone stimulates renal 1-alpha-hydroxylase, increasing production of
active vitamin D (calcitriol), which enhances intestinal calcium absorption.*
4.
Which artery is most commonly occluded in an anterior wall myocardial infarction?
A. Left anterior descending artery
B. Right coronary artery
C. Left circumflex artery
D. Posterior descending artery
E. Marginal artery
Answer: A
Rationale: The left anterior descending artery supplies the anterior wall of the left ventricle and
anterior interventricular septum. Its occlusion produces the most common type of ST-elevation
myocardial infarction.*
5.
A patient with liver cirrhosis develops oesophageal varices. Which vessel is directly responsible for
the increased portal venous pressure?
A. Inferior vena cava
B. Hepatic artery
C. Portal vein
D. Splenic artery
E. Inferior mesenteric artery
Answer: C
Rationale: Portal hypertension results from increased resistance to blood flow through the liver,
causing elevated pressure within the portal venous system and formation of portosystemic collateral
vessels.*
6.
A child presents with recurrent respiratory infections, chronic sinusitis, and situs inversus. Which
cellular structure is defective?
A. Actin filaments
B. Intermediate filaments
C. Dynein arms of cilia
,D. Microfilaments
E. Desmosomes
Answer: C
Rationale: Primary ciliary dyskinesia is caused by defective dynein arms, resulting in impaired ciliary
motility, chronic respiratory infections, infertility, and situs inversus (Kartagener syndrome).*
7.
A patient with severe burns develops hypovolaemic shock. Which hemodynamic change is expected?
A. Increased preload
B. Decreased cardiac output
C. Decreased systemic vascular resistance initially
D. Increased mixed venous oxygen saturation
E. Increased pulmonary capillary wedge pressure
Answer: B
Rationale: Loss of intravascular fluid decreases venous return, reducing preload and cardiac output.
Compensatory vasoconstriction increases systemic vascular resistance.*
8.
Which vitamin deficiency is most likely to cause prolonged prothrombin time due to impaired
synthesis of clotting factors?
A. Vitamin A
B. Vitamin C
C. Vitamin D
D. Vitamin K
E. Vitamin E
Answer: D
Rationale: Vitamin K is required for gamma-carboxylation of clotting factors II, VII, IX, and X, as well
as proteins C and S. Deficiency prolongs the prothrombin time.*
9.
A patient develops numbness over the lateral shoulder following anterior shoulder dislocation.
Which nerve is most likely injured?
A. Radial nerve
B. Musculocutaneous nerve
C. Axillary nerve
D. Median nerve
E. Ulnar nerve
, Answer: C
Rationale: The axillary nerve is commonly injured during anterior shoulder dislocation, causing
deltoid weakness and sensory loss over the lateral shoulder ("regimental badge" area).*
10.
During an osteopathic structural examination, tissue texture changes are noted at T1–T5. These
findings are most consistent with viscerosomatic reflexes involving which organ?
A. Stomach
B. Kidneys
C. Heart
D. Colon
E. Urinary bladder
Answer: C
Rationale: The heart receives sympathetic innervation from T1–T5. Viscerosomatic reflexes at these
spinal levels may be associated with cardiac dysfunction and are evaluated during osteopathic
structural examination.*
11.
A 27-year-old woman presents with fatigue, arthralgias, and a malar rash. Laboratory testing reveals
positive anti-double-stranded DNA antibodies. Which hypersensitivity reaction is primarily
responsible for her disease?
A. Type I hypersensitivity
B. Type II hypersensitivity
C. Type III hypersensitivity
D. Type IV hypersensitivity
E. Type V hypersensitivity
Answer: C
Rationale: Systemic lupus erythematosus is primarily a Type III hypersensitivity reaction involving
immune complex deposition that leads to inflammation and tissue damage in multiple organs.*
12.
A patient has persistent hypertension due to excess aldosterone secretion. Which nephron cell is the
primary target of aldosterone?
A. Macula densa cells
B. Podocytes
C. Proximal tubular cells
D. Principal cells of the collecting duct
E. Mesangial cells
Answer: D
and answers with rationales 2025-2026
Master COMSAE Phase 1 using 100 original board-style practice questions, detailed rationales, and
high-yield explanations for comprehensive COMLEX-USA preparation.
1.
A 19-year-old college student presents with fever, headache, neck stiffness, and a petechial rash.
Cerebrospinal fluid analysis reveals elevated protein, decreased glucose, and neutrophilic
pleocytosis. Which organism is the most likely cause?
A. Streptococcus pneumoniae
B. Neisseria meningitidis
C. Listeria monocytogenes
D. Haemophilus influenzae
E. Cryptococcus neoformans
Answer: B
Rationale: Neisseria meningitidis commonly causes bacterial meningitis in adolescents and young
adults. Petechial rash, meningitis, and rapid progression to septic shock are classic features.*
2.
A patient presents with muscle weakness that improves with repeated use. Autoantibodies are
directed against presynaptic voltage-gated calcium channels. Which disorder is most likely?
A. Myasthenia gravis
B. Lambert-Eaton myasthenic syndrome
C. Multiple sclerosis
D. Guillain-Barré syndrome
E. Amyotrophic lateral sclerosis
Answer: B
Rationale: Lambert-Eaton syndrome results from antibodies against presynaptic calcium channels,
reducing acetylcholine release. Unlike myasthenia gravis, strength often improves with repeated
muscle use.*
3.
A patient has elevated serum calcium and decreased serum phosphate due to excessive secretion of
parathyroid hormone. Which renal enzyme activity is increased?
A. Carbonic anhydrase
B. Renin
C. 1-alpha-hydroxylase
,D. Xanthine oxidase
E. ACE
Answer: C
Rationale: Parathyroid hormone stimulates renal 1-alpha-hydroxylase, increasing production of
active vitamin D (calcitriol), which enhances intestinal calcium absorption.*
4.
Which artery is most commonly occluded in an anterior wall myocardial infarction?
A. Left anterior descending artery
B. Right coronary artery
C. Left circumflex artery
D. Posterior descending artery
E. Marginal artery
Answer: A
Rationale: The left anterior descending artery supplies the anterior wall of the left ventricle and
anterior interventricular septum. Its occlusion produces the most common type of ST-elevation
myocardial infarction.*
5.
A patient with liver cirrhosis develops oesophageal varices. Which vessel is directly responsible for
the increased portal venous pressure?
A. Inferior vena cava
B. Hepatic artery
C. Portal vein
D. Splenic artery
E. Inferior mesenteric artery
Answer: C
Rationale: Portal hypertension results from increased resistance to blood flow through the liver,
causing elevated pressure within the portal venous system and formation of portosystemic collateral
vessels.*
6.
A child presents with recurrent respiratory infections, chronic sinusitis, and situs inversus. Which
cellular structure is defective?
A. Actin filaments
B. Intermediate filaments
C. Dynein arms of cilia
,D. Microfilaments
E. Desmosomes
Answer: C
Rationale: Primary ciliary dyskinesia is caused by defective dynein arms, resulting in impaired ciliary
motility, chronic respiratory infections, infertility, and situs inversus (Kartagener syndrome).*
7.
A patient with severe burns develops hypovolaemic shock. Which hemodynamic change is expected?
A. Increased preload
B. Decreased cardiac output
C. Decreased systemic vascular resistance initially
D. Increased mixed venous oxygen saturation
E. Increased pulmonary capillary wedge pressure
Answer: B
Rationale: Loss of intravascular fluid decreases venous return, reducing preload and cardiac output.
Compensatory vasoconstriction increases systemic vascular resistance.*
8.
Which vitamin deficiency is most likely to cause prolonged prothrombin time due to impaired
synthesis of clotting factors?
A. Vitamin A
B. Vitamin C
C. Vitamin D
D. Vitamin K
E. Vitamin E
Answer: D
Rationale: Vitamin K is required for gamma-carboxylation of clotting factors II, VII, IX, and X, as well
as proteins C and S. Deficiency prolongs the prothrombin time.*
9.
A patient develops numbness over the lateral shoulder following anterior shoulder dislocation.
Which nerve is most likely injured?
A. Radial nerve
B. Musculocutaneous nerve
C. Axillary nerve
D. Median nerve
E. Ulnar nerve
, Answer: C
Rationale: The axillary nerve is commonly injured during anterior shoulder dislocation, causing
deltoid weakness and sensory loss over the lateral shoulder ("regimental badge" area).*
10.
During an osteopathic structural examination, tissue texture changes are noted at T1–T5. These
findings are most consistent with viscerosomatic reflexes involving which organ?
A. Stomach
B. Kidneys
C. Heart
D. Colon
E. Urinary bladder
Answer: C
Rationale: The heart receives sympathetic innervation from T1–T5. Viscerosomatic reflexes at these
spinal levels may be associated with cardiac dysfunction and are evaluated during osteopathic
structural examination.*
11.
A 27-year-old woman presents with fatigue, arthralgias, and a malar rash. Laboratory testing reveals
positive anti-double-stranded DNA antibodies. Which hypersensitivity reaction is primarily
responsible for her disease?
A. Type I hypersensitivity
B. Type II hypersensitivity
C. Type III hypersensitivity
D. Type IV hypersensitivity
E. Type V hypersensitivity
Answer: C
Rationale: Systemic lupus erythematosus is primarily a Type III hypersensitivity reaction involving
immune complex deposition that leads to inflammation and tissue damage in multiple organs.*
12.
A patient has persistent hypertension due to excess aldosterone secretion. Which nephron cell is the
primary target of aldosterone?
A. Macula densa cells
B. Podocytes
C. Proximal tubular cells
D. Principal cells of the collecting duct
E. Mesangial cells
Answer: D
