COMPREHENSIVE OSTEOPATHIC MEDICAL SELF-
ASSESSMENT EXAMINATION (COMSAE) PHASE 1 FORM
113 COMPLETE PRACTICE EXAM QUESTIONS AND
ANSWERS | VERIFIED SOLUTIONS | UPDATED
2026/2027 STUDY GUIDE
Examiner/Administrator: National Board of Osteopathic Medical Examiners (NBOME)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
COMPREHENSIVE OSTEOPATHIC MEDICAL
SELF-ASSESSMENT EXAMINATION
(COMSAE) PHASE 1 FORM 113
2026/2027 EDITION
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
COMPLETE PRACTICE EXAM
100 MULTIPLE-CHOICE QUESTIONS
EXACT OFFICIAL COUNT: 100 QUESTIONS
PASSING SCORE: 70%
TESTING TIME: 120 MINUTES
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
NBOME BLUEPRINT-ALIGNED EXAMINATION || OSTEOPATHIC MEDICAL SCIENCES ||
SYSTEMS-BASED BOARD PREPARATION || COMPREHENSIVE BASIC SCIENCE REVIEW ||
CLINICAL APPLICATION & DIAGNOSTIC REASONING || 100% ORIGINAL VERIFIED
PRACTICE CONTENT || UPDATED ACCORDING TO CURRENT COMLEX-STYLE TESTING
STANDARDS || PROFESSIONAL MEDICAL EXAMINATION PREPARATION || DESIGNED
FOR PHASE 1 BOARD SUCCESS || EDUCATIONAL USE ONLY
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
General Principles, Biochemistry & Physiology (Questions 1–8)
,Q1. A 22-year-old medical student presents with fatigue and intermittent muscle
cramps after beginning an extreme low-carbohydrate diet. Laboratory studies reveal
elevated ketone production. Which enzyme is primarily responsible for the rate-
limiting step in hepatic ketogenesis?
A. Acetyl-CoA carboxylase
B. HMG-CoA synthase
C. Carnitine palmitoyltransferase I
D. Pyruvate dehydrogenase
Correct Answer: 🔴 B. HMG-CoA synthase
Explanation: 🔹 Hepatic mitochondrial HMG-CoA synthase catalyzes the rate-limiting
step of ketogenesis, converting acetoacetyl-CoA into HMG-CoA. Ketogenesis increases
during fasting or carbohydrate restriction due to increased fatty acid oxidation. Acetyl-
CoA carboxylase is involved in fatty acid synthesis, not ketone production. Carnitine
palmitoyltransferase I regulates transport of fatty acids into mitochondria for beta-
oxidation but is not the rate-limiting enzyme of ketogenesis itself. Pyruvate
dehydrogenase links glycolysis to the TCA cycle and is inhibited during fasting states.
Q2. A researcher studying oxygen delivery notes that a patient's oxyhemoglobin
dissociation curve is shifted to the right. Which condition most likely explains this
finding?
A. Decreased 2,3-BPG concentration
B. Carbon monoxide poisoning
C. Metabolic acidosis
D. Hypothermia
Correct Answer: 🔴 C. Metabolic acidosis
Explanation: 🔹 Metabolic acidosis increases hydrogen ion concentration, decreasing
hemoglobin affinity for oxygen and shifting the oxyhemoglobin dissociation curve to the
right. This facilitates oxygen unloading to tissues. Decreased 2,3-BPG, hypothermia, and
carbon monoxide poisoning shift the curve to the left, increasing oxygen affinity and
impairing tissue delivery.
,Q3. A 5-year-old child presents with recurrent bacterial infections and absent thymic
shadow on chest radiograph. Genetic testing demonstrates failure of development of
the third and fourth pharyngeal pouches. Which syndrome is most likely present?
A. Wiskott-Aldrich syndrome
B. DiGeorge syndrome
C. Bruton's agammaglobulinemia
D. Severe combined immunodeficiency
Correct Answer: 🔴 B. DiGeorge syndrome
Explanation: 🔹 DiGeorge syndrome results from 22q11 deletion causing abnormal
development of the third and fourth pharyngeal pouches, leading to thymic aplasia,
hypocalcemia, and T-cell deficiency. Wiskott-Aldrich presents with eczema and
thrombocytopenia. Bruton's agammaglobulinemia causes absent B cells. SCID causes
severe combined T- and B-cell dysfunction but is not associated with pharyngeal pouch
abnormalities.
Q4. A patient with chronic renal failure develops hypocalcemia. Which physiological
mechanism most directly contributes to this electrolyte abnormality?
A. Increased calcitonin secretion
B. Reduced intestinal phosphate absorption
C. Decreased activation of vitamin D
D. Excess aldosterone production
Correct Answer: 🔴 C. Decreased activation of vitamin D
Explanation: 🔹 Diseased kidneys lose the ability to convert 25-hydroxyvitamin D into
active 1,25-dihydroxyvitamin D through impaired 1-alpha hydroxylase activity. This
reduces intestinal calcium absorption, contributing to hypocalcemia. Calcitonin plays a
minor role in chronic renal disease. Intestinal phosphate absorption is not the primary
issue. Aldosterone mainly regulates sodium and potassium balance.
Q5. A scientist inhibits microtubule polymerization in rapidly dividing tumor cells.
Which phase of mitosis is most directly disrupted?
, A. Prophase
B. Metaphase
C. Telophase
D. Cytokinesis
Correct Answer: 🔴 B. Metaphase
Explanation: 🔹 Microtubules form the mitotic spindle necessary for chromosomal
alignment during metaphase. Inhibiting polymerization prevents spindle formation and
arrests cells in metaphase. Prophase involves chromosome condensation, while telophase
and cytokinesis occur after chromosomal separation.
Q6. A patient develops severe diarrhea after prolonged broad-spectrum antibiotic
therapy. Colonoscopy reveals pseudomembranous colitis. Which toxin-mediated
mechanism is responsible?
A. Activation of adenylate cyclase
B. Inhibition of EF-2
C. Inactivation of Rho GTPases
D. Increased guanylate cyclase activity
Correct Answer: 🔴 C. Inactivation of Rho GTPases
Explanation: 🔹 Clostridioides difficile toxins A and B glucosylate Rho GTPases,
disrupting the actin cytoskeleton and damaging intestinal mucosa. Cholera toxin
activates adenylate cyclase. Diphtheria toxin inhibits EF-2. Heat-stable ETEC toxin
increases guanylate cyclase activity.
Q7. A 68-year-old man with emphysema demonstrates increased lung compliance.
Which pathological process most directly accounts for this finding?
A. Fibrotic collagen deposition
B. Loss of elastic tissue recoil
C. Smooth muscle hypertrophy
D. Pulmonary vascular congestion
ASSESSMENT EXAMINATION (COMSAE) PHASE 1 FORM
113 COMPLETE PRACTICE EXAM QUESTIONS AND
ANSWERS | VERIFIED SOLUTIONS | UPDATED
2026/2027 STUDY GUIDE
Examiner/Administrator: National Board of Osteopathic Medical Examiners (NBOME)
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
COMPREHENSIVE OSTEOPATHIC MEDICAL
SELF-ASSESSMENT EXAMINATION
(COMSAE) PHASE 1 FORM 113
2026/2027 EDITION
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
COMPLETE PRACTICE EXAM
100 MULTIPLE-CHOICE QUESTIONS
EXACT OFFICIAL COUNT: 100 QUESTIONS
PASSING SCORE: 70%
TESTING TIME: 120 MINUTES
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
NBOME BLUEPRINT-ALIGNED EXAMINATION || OSTEOPATHIC MEDICAL SCIENCES ||
SYSTEMS-BASED BOARD PREPARATION || COMPREHENSIVE BASIC SCIENCE REVIEW ||
CLINICAL APPLICATION & DIAGNOSTIC REASONING || 100% ORIGINAL VERIFIED
PRACTICE CONTENT || UPDATED ACCORDING TO CURRENT COMLEX-STYLE TESTING
STANDARDS || PROFESSIONAL MEDICAL EXAMINATION PREPARATION || DESIGNED
FOR PHASE 1 BOARD SUCCESS || EDUCATIONAL USE ONLY
━━━━━━━━━━━━━━━━━━━━━━━━━━━━
General Principles, Biochemistry & Physiology (Questions 1–8)
,Q1. A 22-year-old medical student presents with fatigue and intermittent muscle
cramps after beginning an extreme low-carbohydrate diet. Laboratory studies reveal
elevated ketone production. Which enzyme is primarily responsible for the rate-
limiting step in hepatic ketogenesis?
A. Acetyl-CoA carboxylase
B. HMG-CoA synthase
C. Carnitine palmitoyltransferase I
D. Pyruvate dehydrogenase
Correct Answer: 🔴 B. HMG-CoA synthase
Explanation: 🔹 Hepatic mitochondrial HMG-CoA synthase catalyzes the rate-limiting
step of ketogenesis, converting acetoacetyl-CoA into HMG-CoA. Ketogenesis increases
during fasting or carbohydrate restriction due to increased fatty acid oxidation. Acetyl-
CoA carboxylase is involved in fatty acid synthesis, not ketone production. Carnitine
palmitoyltransferase I regulates transport of fatty acids into mitochondria for beta-
oxidation but is not the rate-limiting enzyme of ketogenesis itself. Pyruvate
dehydrogenase links glycolysis to the TCA cycle and is inhibited during fasting states.
Q2. A researcher studying oxygen delivery notes that a patient's oxyhemoglobin
dissociation curve is shifted to the right. Which condition most likely explains this
finding?
A. Decreased 2,3-BPG concentration
B. Carbon monoxide poisoning
C. Metabolic acidosis
D. Hypothermia
Correct Answer: 🔴 C. Metabolic acidosis
Explanation: 🔹 Metabolic acidosis increases hydrogen ion concentration, decreasing
hemoglobin affinity for oxygen and shifting the oxyhemoglobin dissociation curve to the
right. This facilitates oxygen unloading to tissues. Decreased 2,3-BPG, hypothermia, and
carbon monoxide poisoning shift the curve to the left, increasing oxygen affinity and
impairing tissue delivery.
,Q3. A 5-year-old child presents with recurrent bacterial infections and absent thymic
shadow on chest radiograph. Genetic testing demonstrates failure of development of
the third and fourth pharyngeal pouches. Which syndrome is most likely present?
A. Wiskott-Aldrich syndrome
B. DiGeorge syndrome
C. Bruton's agammaglobulinemia
D. Severe combined immunodeficiency
Correct Answer: 🔴 B. DiGeorge syndrome
Explanation: 🔹 DiGeorge syndrome results from 22q11 deletion causing abnormal
development of the third and fourth pharyngeal pouches, leading to thymic aplasia,
hypocalcemia, and T-cell deficiency. Wiskott-Aldrich presents with eczema and
thrombocytopenia. Bruton's agammaglobulinemia causes absent B cells. SCID causes
severe combined T- and B-cell dysfunction but is not associated with pharyngeal pouch
abnormalities.
Q4. A patient with chronic renal failure develops hypocalcemia. Which physiological
mechanism most directly contributes to this electrolyte abnormality?
A. Increased calcitonin secretion
B. Reduced intestinal phosphate absorption
C. Decreased activation of vitamin D
D. Excess aldosterone production
Correct Answer: 🔴 C. Decreased activation of vitamin D
Explanation: 🔹 Diseased kidneys lose the ability to convert 25-hydroxyvitamin D into
active 1,25-dihydroxyvitamin D through impaired 1-alpha hydroxylase activity. This
reduces intestinal calcium absorption, contributing to hypocalcemia. Calcitonin plays a
minor role in chronic renal disease. Intestinal phosphate absorption is not the primary
issue. Aldosterone mainly regulates sodium and potassium balance.
Q5. A scientist inhibits microtubule polymerization in rapidly dividing tumor cells.
Which phase of mitosis is most directly disrupted?
, A. Prophase
B. Metaphase
C. Telophase
D. Cytokinesis
Correct Answer: 🔴 B. Metaphase
Explanation: 🔹 Microtubules form the mitotic spindle necessary for chromosomal
alignment during metaphase. Inhibiting polymerization prevents spindle formation and
arrests cells in metaphase. Prophase involves chromosome condensation, while telophase
and cytokinesis occur after chromosomal separation.
Q6. A patient develops severe diarrhea after prolonged broad-spectrum antibiotic
therapy. Colonoscopy reveals pseudomembranous colitis. Which toxin-mediated
mechanism is responsible?
A. Activation of adenylate cyclase
B. Inhibition of EF-2
C. Inactivation of Rho GTPases
D. Increased guanylate cyclase activity
Correct Answer: 🔴 C. Inactivation of Rho GTPases
Explanation: 🔹 Clostridioides difficile toxins A and B glucosylate Rho GTPases,
disrupting the actin cytoskeleton and damaging intestinal mucosa. Cholera toxin
activates adenylate cyclase. Diphtheria toxin inhibits EF-2. Heat-stable ETEC toxin
increases guanylate cyclase activity.
Q7. A 68-year-old man with emphysema demonstrates increased lung compliance.
Which pathological process most directly accounts for this finding?
A. Fibrotic collagen deposition
B. Loss of elastic tissue recoil
C. Smooth muscle hypertrophy
D. Pulmonary vascular congestion
