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COMSAE Phase 1 Form 115 Practice Exam
Questions And Well Graded Solutions With
Rationales Updated 2026- 2027
Master your COMLEX Level 1 diagnostic prep with this comprehensive study guide for the COMSAE Phase 1 Form 115 exam. This document provides clear practice questions alongside bolded correct answers and detailed, italicized rationales covering core medical sciences, high-yield organ systems, and OMM/OPP concepts. Perfect for tracking diagnostic milestones, evaluating board readiness, and identifying weak areas. Score higher, study smarter, and pass your osteopathic boards with confidence!
Question 1
A 64-year-old male presents to the emergency department with severe, crushing chest pain that radiates to his left arm. An electrocardiogram (ECG) reveals ST- segment elevations in leads II, III, and aVF. Which of the following coronary arteries is most likely occluded? A) Left anterior descending artery B) Left circumflex artery C) Right coronary artery D) Left main coronary artery Rationale: ST-segment elevations in leads II, III, and aVF indicate an acute inferior wall myocardial infarction. The right coronary artery (RCA) supplies the inferior wall of the ventricles in the majority of patients (right-dominant circulation). Occlusion of the left anterior descending artery would present with changes in the anterior leads (V1-V4), while the left circumflex artery affects the lateral leads (I, aVL, V5-V6).
Question 2
A 22-year-old female presents to her gynecologist with abdominal bloating and pelvic pain. An ultrasound reveals a large, unilocular ovarian cyst filled with clear fluid. A biopsy of the tissue confirms a benign epithelial tumor lined with ciliated columnar epithelium. Which of the following is the most likely diagnosis? A) Serous cystadenoma B) Mucinous cystadenoma C) Brenner tumor D) Granulosa cell tumor
Rationale: Serous cystadenomas are the most common benign epithelial ovarian tumors and are typically filled with clear, serous fluid and lined with ciliated columnar epithelium. Mucinous cystadenomas are lined by mucus-secreting cells and filled with thick mucin. Brenner tumors contain bladder-like epithelium (transitional cells). Granulosa cell tumors are sex cord-stromal tumors that secrete estrogen and feature Call-Exner bodies.
Question 3
A 45-year-old female presents with progressive fatigue, generalized weakness, and a distinct darkening of her skin, particularly around her palmar creases and gums. Laboratory analysis reveals a serum sodium level of 128 mEq/L (normal: 135- 145 mEq/L) and a serum potassium level of 5.6 mEq/L (normal: 3.5-5.0 mEq/L). Primary adrenal insufficiency is suspected. Which of the following hormones is primarily deficient in this patient causing the electrolyte abnormalities? A) Cortisol B) Aldosterone C) Epinephrine D) ACTH Rationale: Primary adrenal insufficiency (Addison's disease) involves the destruction of all layers of the adrenal cortex. While a deficiency in cortisol causes fatigue and upregulates ACTH (leading to hyperpigmentation), the severe hyponatremia and hyperkalemia are directly caused by a lack of aldosterone. Aldosterone normally promotes sodium reabsorption and potassium excretion in the renal collecting ducts.
Question 1
A 28-year-old female presents with irregular menses, hirsutism, and acne. Ultrasound reveals multiple small follicles along the periphery of both ovaries, resembling a "string of pearls." This patient is at an increased risk for developing which of the following malignancies? A) Cervical carcinoma B) Endometrial carcinoma C) Granulosa cell tumor D) Serous cystadenocarcinoma
Rationale: Barrett's esophagus is a complication of chronic GERD characterized by intestinal metaplasia, where the normal stratified squamous epithelium of the lower esophagus transforms into simple columnar epithelium. The hallmark histological finding that confirms intestinal metaplasia is the presence of mucin-producing goblet cells.
Question 4
A 19-year-old college student presents with a high fever, severe headache, and neck stiffness. Physical examination reveals a petechial rash on his lower extremities. A lumbar puncture is performed. Gram stain of the cerebrospinal fluid reveals Gram- negative diplococci. Which of the following is the most appropriate initial empiric pharmacotherapy? A) Vancomycin B) Ceftriaxone C) Ampicillin D) Gentamicin Rationale: The presentation of fever, altered mental status, nuchal rigidity, a petechial rash, and Gram-negative diplococci is diagnostic for Neisseria meningitidis meningitis. Third-generation cephalosporins like ceftriaxone penetrate the blood- brain barrier effectively and serve as the first-line treatment.
Question 5
A 55-year-old female with a history of rheumatoid arthritis presents with abdominal pain. She has been taking high-dose naproxen daily for the past six months. Laboratory findings reveal a microcytic, hypochromic anemia. Which of the following mechanisms is responsible for her primary gastrointestinal pathology? A) Direct chemical toxicity to the gastric epithelium B) Stimulation of histamine H2 receptors C) Inhibition of cyclooxygenase-1 (COX-1) D) Upregulation of mucosal prostaglandin production
Rationale: Nonsteroidal anti-inflammatory drugs (NSAIDs) like naproxen inhibit cyclooxygenase-1 (COX-1), which is responsible for synthesizing cytoprotective prostaglandins ((PGE{2}) and (PGI_{2})) in the gastric mucosa. Decreased prostaglandin levels reduce mucus and bicarbonate secretion, increasing susceptibility to peptic ulcer disease and subsequent occult bleeding._
Question 6
A 4-year-old boy is brought to the clinic due to worsening developmental delays and coarse facial features. Physical examination reveals hepatosplenomegaly and restricted joint mobility. Urinalysis shows elevated levels of dermatan sulfate and heparan sulfate. The patient is diagnosed with Hurler syndrome. Which enzyme is deficient? A) (\alpha )-L-iduronidase B) Iduronate sulfatase C) Hexosaminidase A D) Sphingomyelinase Rationale: Hurler syndrome is an autosomal recessive mucopolysaccharidosis (MPS I) caused by a deficiency in (\alpha )-L-iduronidase. This leads to the accumulation of dermatan sulfate and heparan sulfate. Hunter syndrome (MPS II) is X-linked recessive and caused by an iduronate sulfatase deficiency.
Question 7
A 62-year-old female presents with sudden-onset severe pain and redness in her left eye, accompanied by a halo around lights and nausea. On examination, the left pupil is mid-dilated and fixed. Intraxocular pressure is significantly elevated. Which of the following medications is contraindicated in this patient? A) Pilocarpine B) Acetazolamide C) Atropine D) Timolol
Rationale: The patient exhibits signs of Wernicke-Korsakoff syndrome, which comprises Wernicke encephalopathy (confusion, ataxia, ophthalmoplegia) and Korsakoff psychosis (confabulation, memory loss). This condition is caused by a severe thiamine (vitamin B1) deficiency, which impairs glucose utilization in the brain.
Question 10
A 30-year-old male presents with severe pain, swelling, and redness in his right first metatarsophalangeal (MTP) joint that started suddenly overnight. Joint aspirate under polarized light microscopy demonstrates negatively birefringent, needle- shaped crystals. Which of the following is the first-line treatment for an acute flare in this patient if he has no comorbidities? A) Allopurinol B) Febuxostat C) Indomethacin D) Probenecid Rationale: Negatively birefringent, needle-shaped crystals confirm acute gouty arthritis. Acute flares are managed with anti-inflammatory drugs like NSAIDs (e.g., indomethacin), colchicine, or glucocorticoids. Urate-lowering therapies like allopurinol or febuxostat should not be initiated during an acute flare, as sudden shifts in serum uric acid can worsen or prolong the attack.
Question 11
A 29-year-old woman at 32 weeks gestation presents with sudden-onset, painless vaginal bleeding. Ultrasound confirms that the placenta is completely covering the internal cervical os. Which of the following is the most appropriate management plan for delivery? A) Induction of labor at 37 weeks B) Vaginal delivery at term
C) Scheduled Cesarean delivery at 36-37 weeks D) Emergent Cesarean delivery immediately Rationale: This patient has placenta previa. Because the placenta obstructs the cervical os, vaginal delivery is strictly contraindicated due to the risk of catastrophic maternal and fetal hemorrhage. Stable patients are managed expectantly with pelvic rest and delivered via scheduled Cesarean section between 36 and 37 weeks.
Question 12
A 68-year-old male presents with worsening urinary urgency, frequency, and nocturia over the past year. Rectal examination reveals a smooth, symmetrically enlarged prostate without nodules. Serum PSA is mildly elevated. Biopsy of the prostate tissue would most likely show hyperplasia of which region? A) Transition zone B) Peripheral zone C) Central zone D) Anterior fibromuscular stroma Rationale: Benign Prostatic Hyperplasia (BPH) predominantly affects the transition zone of the prostate, which surrounds the urethra. Hyperplasia in this area causes compression of the prostatic urethra, leading to obstructive lower urinary tract symptoms. Prostate adenocarcinoma, by contrast, arises most commonly in the peripheral zone.
Question 13
A 3-year-old girl is brought to the physician due to chronic, recurrent respiratory infections and bulky, foul-smelling stools. A sweat chloride test returns a value of 75 mEq/L (normal: <40 mEq/L). The primary genetic mutation involved in this disease alters a channel that transports which of the following ions? A) Sodium B) Potassium
C) Auer rods within myeloblasts D) Reed-Sternberg cells Rationale: The clinical picture of bone pain, hypercalcemia, renal insufficiency, and an M-spike on SPEP points to Multiple Myeloma. Multiple Myeloma is a neoplastic proliferation of a single clone of plasma cells in the bone marrow. Diagnostic criteria include a bone marrow biopsy showing (\geq 10%) clonal plasma cells.
Question 16
A 24-year-old graduate student presents with a 2-month history of bloody diarrhea, lower abdominal cramping, and weight loss. Colonoscopy reveals continuous mucosal inflammation and superficial ulcerations extending from the rectum up to the mid-descending colon. Biopsy shows crypt abscesses. What is the most likely diagnosis? A) Crohn's disease B) Ulcerative colitis C) Celiac disease D) Ischemic colitis Rationale: Ulcerative colitis is characterized by continuous mucosal and submucosal inflammation that always starts in the rectum and extends proximally. Crypt abscesses containing neutrophils are a classic histological finding. Crohn's disease, conversely, features transmural inflammation, skip lesions, and non-caseating granulomas.
Question 17
A 14-year-old boy presents to his pediatrician with a 3-week history of worsening pain just below his right knee. He notes the pain is exacerbated by running and jumping during basketball practice. Examination reveals exquisite tenderness and swelling over the tibial tubercle. What is the most likely underlying pathology?
A) Traction apophysitis of the tibial tubercle B) Avascular necrosis of the femoral head C) Inflammation of the patellar tendon insertion on the patella D) Microfractures of the distal femur Rationale: Osgood-Schlatter disease is a traction apophysitis of the tibial tubercle caused by repetitive strain from the quadriceps femoris muscle action on the patellar tendon. It is highly common in adolescent athletes undergoing rapid growth spurts.
Question 18
A 53-year-old postmenopausal female presents with vaginal bleeding. Endometrial biopsy confirms well-differentiated endometrial adenocarcinoma. Immunohistochemical staining confirms high expression of estrogen receptors. Which of the following cell types is the primary source of excess estrogen production in a postmenopausal woman? A) Ovarian granulosa cells B) Adrenal cortex fasciculata cells C) Adipose tissue stromal cells D) Endometrial glandular cells Rationale: In postmenopausal women, the ovaries cease follicular estrogen production. Peripheral aromatization of adrenal androgens (specifically androstenedione) into estrone by the enzyme aromatase in adipose tissue becomes the primary source of estrogen. Obesity significantly upregulates this pathway.
Question 19
A 38-year-old male injection drug user presents with a fever, chills, and a new murmur. Echocardiography reveals a large, mobile vegetation on the tricuspid valve. Blood cultures grow Gram-positive, catalase-positive, coagulase-positive cocci in clusters. Which organism is responsible?
A) Postsynaptic acetylcholine receptors B) Presynaptic voltage-gated calcium channels C) Myelin sheath proteins D) Acetylcholinesterase enzyme Rationale: Myasthenia gravis is an autoimmune disorder caused by antibodies against the postsynaptic nicotinic acetylcholine receptors at the neuromuscular junction. It features fatigable skeletal muscle weakness. Edrophonium prevents acetylcholine breakdown, temporarily overcoming the competitive antibody blockade.
Question 22
A 44-year-old male with a history of mechanical aortic valve replacement presents for a routine checkup. He is taking warfarin for anticoagulation. His international normalized ratio (INR) is therapeutic at 2.5. Which of the following coagulation factors has its synthesis blocked earliest after starting warfarin therapy due to having the shortest half-life? A) Factor II B) Factor VII C) Factor IX D) Factor X Rationale: Warfarin acts by inhibiting vitamin K epoxide reductase, blocking the (\gamma )-carboxylation of factors II, VII, IX, and X, as well as proteins C and S. Factor VII has the shortest half-life (approximately 6 hours) among the vitamin K- dependent factors, making it the earliest factor depleted.
Question 23
A 9-month-old male infant is brought to the clinic due to persistent skin infections and recurrent otitis media. Laboratory workup reveals profoundly low levels of serum IgG, IgA, and IgM. B-cell counts are virtually undetectable in peripheral blood, while T-cell levels are completely normal. What is the inheritance pattern of this disease?
A) Autosomal recessive B) Autosomal dominant C) X-linked recessive D) X-linked dominant Rationale: This patient has X-linked (Bruton) agammaglobulinemia, caused by a mutation in the Bruton tyrosine kinase (BTK) gene. This defect halts B-cell maturation in the bone marrow, leading to an absence of peripheral B cells and all immunoglobulin classes. The condition follows an X-linked recessive inheritance pattern.
Question 24
A 45-year-old male presents with progressive shortness of breath and a dry cough. A chest X-ray shows bilateral interstitial infiltrates and calcified pleural plaques along the diaphragm. He mentions he worked in ship demolition and insulation installation for over twenty years. This patient is at the highest absolute risk of developing which malignancy? A) Bronchogenic carcinoma B) Mesothelioma C) Laryngeal carcinoma D) Renal cell carcinoma Rationale: Asbestos exposure causes pleural plaques and interstitial fibrosis. While asbestos exposure is the only major risk factor for mesothelioma, the absolute risk of developing bronchogenic (lung) carcinoma is significantly higher than that of mesothelioma in asbestos-exposed individuals, especially if they smoke.
Question 25
A 60-year-old male with a history of hyperlipidemia presents with sudden, severe chest pain that radiates to his back between his scapulae, described as a "tearing" sensation. His blood pressure is 185/105 mmHg. A chest X-ray shows widening of the mediastinum. What is the primary underlying pathological process?
A) Villous atrophy and crypt hyperplasia B) Transmural inflammation with non-caseating granulomas C) Macrophages filled with PAS-positive bacilli D) Normal villi with eosinophilic infiltrates Rationale: This patient has Celiac disease, suggested by the malabsorptive symptoms, dermatitis herpetiformis (the vesicular rash), and anti-tTG antibodies. The characteristic duodenal biopsy findings include blunting/atrophy of the intestinal villi, crypt hyperplasia, and increased intraepithelial lymphocytes.
Question 28
A 58-year-old male presents with generalized weakness and darkening of his skin. Laboratory results show fasting plasma glucose of 180 mg/dL and markedly elevated serum ferritin and transferrin saturation. A liver biopsy stains positive with Prussian blue. Which of the following complications is this patient at highest risk for developing? A) Cholelithiasis B) Hepatocellular carcinoma C) Hepatic adenoma D) Budd-Chiari syndrome Rationale: The triad of hyperpigmentation ("bronze skin"), diabetes mellitus, and iron overload (elevated ferritin) signifies hereditary hemochromatosis. Prussian blue stains iron deposits blue. Hereditary hemochromatosis leads to micronodular cirrhosis, significantly escalating the risk for hepatocellular carcinoma.
Question 29
A 22-year-old female medical student undergoes a routine wellness exam. A CBC reveals a mild microcytic anemia with a hemoglobin of 10.5 g/dL and a mean corpuscular volume (MCV) of 68 fL. Her red blood cell count is elevated at (5. \times 10^{12}/\text{L}). Hemoglobin electrophoresis shows an elevated HbA2 level of 5.5% (normal: 1.5-3.5%). What is the diagnosis?
A) Iron deficiency anemia B) (\beta )-thalassemia minor C) (\alpha )-thalassemia trait D) Anemia of chronic disease Rationale: (\beta )-thalassemia minor is caused by a heterozygous mutation in the (\beta )-globin gene, resulting in mild microcytic anemia, a normal or elevated RBC count, and a compensatory increase in (\text{HbA}{2}) ((\alpha_2\delta_2)) on hemoglobin electrophoresis._
Question 30
A 68-year-old male with a long history of heavy smoking presents with unintentional weight loss, a persistent cough, and hemoptysis. Laboratory evaluation reveals a serum calcium level of 12.2 mg/dL with a suppressed parathyroid hormone (PTH) level. A chest CT demonstrates a central hilar mass. What is the most likely histological diagnosis? A) Adenocarcinoma B) Squamous cell carcinoma C) Small cell carcinoma D) Large cell carcinoma Rationale: Squamous cell carcinoma of the lung is classically associated with smoking, located centrally near the hilum, and can produce parathyroid hormone- related protein (PTHrP). PTHrP mimics PTH action, causing hypercalcemia while suppressing endogenous PTH production.
Question 31
A 4-year-old child presents with a high fever for 6 days, bilateral non-exudative conjunctivitis, a polymorphous maculopapular rash on his trunk, and erythema and swelling of his hands and feet. His tongue appears bright red and bumpy. What is the most serious potential complication if this condition is left untreated?
A) Acute appendicitis B) Acute diverticulitis C) Acute mesenteric ischemia D) Ruptured abdominal aortic aneurysm Rationale: Acute mesenteric ischemia is caused by an embolic occlusion of the mesenteric arteries, frequently originating from the left atrium in patients with atrial fibrillation. The classic clinical presentation is severe, poorly localized abdominal pain out of proportion to physical exam findings.
Question 34
A 35-year-old male undergoes an appendectomy. During the procedure, the surgeon identifies a small, well-circumscribed, yellow tumor at the tip of the appendix. Histology confirms a neuroendocrine tumor that stains positive for chromogranin and synaptophysin. If this tumor metastasizes to the liver, which substance's metabolites in the urine would confirm carcinoid syndrome? A) 5-HIAA B) VMA C) Metanephrine D) Homovanillic acid Rationale: Carcinoid tumors are neuroendocrine malignancies that secrete serotonin. Serotonin is metabolized by monoamine oxidase in the liver into 5- hydroxyindoleacetic acid (5-HIAA), which is excreted in urine. 24-hour urinary 5- HIAA measurement is used to diagnose carcinoid syndrome.
Question 35
A 63-year-old male presents with worsening dyspnea on exertion and a chronic cough. Pulmonary function testing demonstrates an (\text{FEV}1/\text{FVC}) ratio of 55% (predicted: >70%). His diffusion capacity for carbon monoxide ((\text{DL}{CO})) is decreased. Which of the following processes best describes the structural remodeling in this patient's lungs?
A) Reversible bronchoconstriction with eosinophilic infiltrates B) Destruction of alveolar walls and permanent airspace enlargement C) Hyperplasia of mucus-secreting goblet cells in large airways D) Fibrotic obliteration of alveolar septa with honeycombing Rationale: An (\text{FEV}1/\text{FVC}) ratio (< 70%) establishes obstructive lung disease. A reduction in (\text{DL}{CO}) differentiates emphysema from chronic bronchitis, reflecting the permanent destruction of alveolar walls and loss of gas- exchange surface area.
Question 36
A 22-year-old male college student presents with a 3-week history of low-grade fever, a nonproductive cough, and a mild headache. A chest X-ray reveals diffuse interstitial infiltrates that look significantly worse than his mild clinical appearance suggests. Cold agglutinin titers are elevated. Which of the following is the most likely causative pathogen? A) Streptococcus pneumoniae B) Mycoplasma pneumoniae C) Legionella pneumophila D) Chlamydia psittaci Rationale: Mycoplasma pneumoniae is the classic cause of "walking pneumonia" in young adults, where chest X-ray findings appear more severe than clinical symptoms. The infection stimulates production of IgM antibodies that agglutinate red blood cells at cold temperatures (cold agglutinins).
Question 37
A 45-year-old female presents with a painless lump in her right breast. Mammography reveals a stellate, radiodense mass with microcalcifications. A core needle biopsy demonstrates cords and nests of malignant epithelial cells embedded within a dense, fibrous stroma. What is the most likely diagnosis?
