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NBME 18 – Questions and Answers | Complete Step 1 Practice Exam with Explanations (2025/2026 Edition)

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This document contains the complete set of NBME 18 questions and verified answers, updated for 2025/2026. It serves as a comprehensive review tool for USMLE Step 1 preparation, covering all key systems and disciplines including physiology, pathology, pharmacology, microbiology, biochemistry, and behavioral science. Each question includes the correct answer and clear explanation to strengthen understanding of high-yield Step 1 concepts and test-taking strategies. Ideal for medical students seeking an authentic NBME-style practice experience.

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NBME 18
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NBME 18

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Subido en
3 de noviembre de 2025
Número de páginas
15
Escrito en
2025/2026
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NBME 18 Questions and Answers
1. Block 1 part 1

1. 56-year-old man comes with vague right-sided flank pain and 7-lb weight loss over past 6 weeks. No recent trauma or back strain. Urine is darker than usual over 2 weeks.
Renal ultrasound shows 1.5-cm solid mass in upper portion of right kidney. Urine shows 50 erythrocytes, 6 leukocytes, no bacteria. Dx?
- Renal cell carcinoma

2. 22-year-old man who is a professional cyclist undergoes extensive physiologic testing as part of his training regimen. His resting pulse is 33/min, and blood pressure is110/62
mm Hg. Echocardiography shows dilated ventricles with normal function and a left ventricular ejection fraction of 75%. Which of the following best describes the findings in this
patient?
- Eccentric hypertrophy

3. During a clinical study of calcium and phosphorus metabolism, a 50-year-old man undergoes series of lab studies. His serum Ca, PO4 and PTH are normal. He is given
infusion 2 g Calcium chloride over 2 hours. His serum Ca concentration now is 11.5mg/dl. Compared with pre infusion levels, the serum concentration of which of the following
substances is likely to be increased at this time?
- 24,25-Dihydroxycholecalciferol

4. 70-year-old man comes with skin blistering for 1 week. No oral lesions. Physical shows tense bullae in joint folds of upper and lower extremities. Biopsy shows subepidermal
blister formation. Immunofluorescence microscopy shows antibodies against proteins at the dermal-epidermal junction. Target by antibodies?
- Hemidesmosome

5. 63-year-old man with abnormal blood pressure. 6 months ago, bp was 135/85. Today bp 170/98. Bruit heard over left renal artery. CT angio shows left arterial stenosis.
Labs?
- Total peripheral resistance increased, plasma renin activity increased, serum aldosterone concentration increased

6. 35-year-old woman with 3-month progressive shortness of breath with exertion. RR 26. Physical shows jvd and prominent a wave. Lungs clear. Cardiac exam shows loud
pulmonic component of S2 and right-sided S4 gallop. Increased pulmonary expression of what?
- Endothelin-1

7. 30-year-old woman with 2-years of numbness, blanching, and bluish color to ears, fingers and toes after emotional upset or cold exposure. Vitals and PE normal. Avoid taking
which drug?
- Phenylephrine

8. 35-year-old woman with 2-day history of blistering lesions on sun-exposed face, arms and hands. Recurrent episodes of skin lesions over several years. Taking oral
contraceptives for 15y. PE shows fluid-filled vesicles and bullae. Labs: AST increased, ALT increased, total porphyrin increased, urine uroporphyrin III increased. Precursor to
uroporphyrin?
- Succinyl CoA

9. 65-year-old with sudden onset generalized tonic-clonic seizures. Personality change last 6 months; used to be mild mannered and now verbally abusive. CT shows single
mass enhances with contrast in right frontal lobe and crosses to left hemisphere through corpus callosum. Dx?
- High-grade fibrillary astrocytoma

10. 3-week-old male newborn with recurrent vomiting after feeding since birth, and eager to feed after vomiting. Abdominal exam shows firm, mobile mass in epigastrum to right
of midline. Dx description?
- Single primary development defect

11. 39-year-old man with 1-week of red spots on shins, joint pain and fatigue. PE shows purpura over lower extremities. Liver palpated 4 cm below costal margin. Labs: WBC
10,000, AST 142, ALT 154, hepatitis C virus RNA positive, anti-hepatitis C virus antibody positive, cryoglobulins positive, C4 120 (N=350-600), urine protein 4+, urine RBC
numerous. Hypersensitivity reaction?
- Type III (immune complex-mediated)

12. 45-year-old man with hypertension not compliant with medications. bp 160/100. Cardiac exam shows apical impulse displaced laterally, loud S2 and S4 gallop. Echo shows
thickening of left ventricular wall. Mechanism of change in cardiac muscle?
- Transcription factor c-Jun: increased, beta-myosin heave chain: increased, endothelin: increased

13. 70-year-old man with early morning awakening, decreased energy, difficulty concentrating, anhedonia, psychomotor retardation, depressed mood for 3 months. He had
myocardial infarction and nonsustained ventricular tachycardia 2 years ago. Tx?
- Paroxetine

14. 5-year-old boy with motion sickness. Planning vacation to Australia, and wants diphenhydramine for motion sickness. Mechanism of action for motion sickness?
- Antagonist at muscarinic-3 (M3) receptors

15. Newborn is found to have a cervical rib. Transformation of seventh cervical segment to thoracic identity. Which is true of HOX gene alteration?
- Expression of a HOX gene normally expressed only caudal to C7

16. 28-year-old man with ulcerative colitis, history of partial colectomy, and improved rectal bleeding and diarrhea since then. Meds include mesalamine, hydrocodone and
acetaminophen. He says, "I've been taking so much of my opiate prescription that I ran out and stole some from my job." Next step?
- Discuss treatment options and a referral for detoxification program

17. 66-year-old man dies 7 days after myocardial infarction. Gross of heart shown (perforated interventricular wall). Histology?
- Erythrocytes, cellular debris, macrophages, and early granulation tissue

18. 16-year-old boy who frequently thinks about sex, daydreams about girls before going to sleep, and masturbates one to two times daily. After counseling about safe sex, best
next step?
- Schedule next routine examination

19. 18-year-old man comes with cracked lips and peeling sunburned skin. Works as lifeguard. PE shows desquamation of sunburned skin. Lips are dry and cracked. Petrolatum
to lips may reduce lip symptoms by which of following effects of the compound?
- Barrier

20. 29-year-old woman comes to the physician because of irregular menstrual periods since menarche at the age of 12. She is 5.3Ft and weighs 86kgs. BMI 34. She is
evaluated and a diagnosis of PCOS is made. After explaining the diagnosis, the physician discusses behavioral changes, including dietary modification and exercise as part of
her treatment. Which of the following will ensure adherence?
- Provide follow ups to monitor progress in attaining her goal

21. 30-year-old man in bicycle collision and hits right shoulder forcefully. Unable to flex right elbow with decreased sensation to pinprick over right lateral forearm. Brachial
plexus lesion?
- E (musculocutaneous nerve)

22. 67-year-old man with 1 year progressive difficulty writing and walking. Pt is stooped and talks slowly. PE shows bland facial expression, fine resting tremor in both hands, no
tremor when moves, walks with difficulty starting and stopping, cogwheel rigidity. Brain tissue histology shown as well as gross cross sections of midbrain both normal and
diseased. Substance referred to by arrow?
- Alpha-synuclein
Dr G Bhanu Prakash

, 23. 25-year-old woman with polycystic kidneys and 3-month history of weakness, fatigue, headaches, hypertension, loss of appetite and itching. Cr 4. Labs?
- bicarb (HCO3-) decreased, inorganic phosphorous (PO4) increased, parathyroid hormone increased

24. 32-year-old woman brought in after 10-foot fall from ladder. PE suggests severe hemorrhage and shock. Xray shows fracture of left ninth and tenth ribs. Organ injured?
- Spleen

25. 26-year-old man comes in 2 hours after injuring arm skiing. Sensation to pinprick absent over lateral aspect of shoulder. Xray of right shoulder shown (fracture of surgical
neck of humerus). Nerve damaged?
- Axillary


Block 1 Part 2

26. 50-year-old woman with COPD comes with 3 months of progressive shortness of breath. Physical shows JVD, loud pulmonary component of S2. Pulmonary function tests
show FEV1:FVC ratio of 20% and decreased diffusing capacity for carbon monoxide. Which is decreased in pulmonary vascular smooth muscle?
- Endothelial nitric oxide synthase production

27. An experimental animal is created that has a defect in an innate gastrointestinal defense mechanism. Organism is found to have decreased HCl prod. After 2 months on
biopsy gastric fundus and body show decreased mucosal thickness and hyperplasia of enterochromaffin like cells. This closely resembles?
- Chronic gastritis

28. 63-year-old woman with 2-week history of daily episodes of severe, lancinating, left-sided facial pain. Pain lasts 30 to 60 seconds and shoots down ear along jawline.
Precipitated by chewing or brushing teeth. Dx?
- Trigeminal neuralgia

29. 45-year-old homeless man found unconscious. Breath smells of alcohol. Vitals stable. PE shows bronzed skin and spider angiomata on chest. Labs: hemoglobin 10,
hematocrit 30%, MCV 110, WBC 9000, platelets 160,000, ferritin 200, b12 500, folate 20. Blood smear shows hypersegmented neutrophils and 3+ oval macrocytes. Labs?
- Methylmalonic acid: normal, Homocysteine: increased

30. 68-year-old man with creatinine 2.3 due to chronically increased hydrostatic pressure in Bowman space. Cause?
- Benign prostatic hyperplasia

31. 70-year-old woman comes to the physician because of increasingly severe pain in the right knee over the past 3 months. She has fallen repeatedly. She has a 10 year
history of symptomatic osteitis deformans. She has bowed tibia and tenderness of the proximal right tibia. an X ray shows a fracture of the proximal tibia with elevated
periostium and sunburst pattern. an xray of lungs shows pulmonary nodules of various sizes. which of the following findings is most likely on biopsy.
- Pleomorphic neoplastic cells producing new woven bone

32. 30-year-old woman with a long-standing history of pelvic inflammatory disease has surgical resection of a scarred segment of a fallopian tube. Which of the following
inflammatory cells is most likely to be found in the resected specimen?
- Macrophages

33. 67-year-old woman with atrial fibrillation with sudden onset severe abdominal pain. Ex-lap shows embolus in superior mesenteric artery with complete occlusion of middle
colic artery. Ischemic changes where?
- Small intestine, ascending colon, and part of the transverse colon

34. 68-year-old man with alcoholism comes for fever, chills and productive cough of purulent sputum for 3 days. Blood cultures positive. Gram stain: gram-positive, lancet-
shaped diplococci. Vaccine is against which bacterial component?
- Capsular polysaccharide

35. Patient making sexual advances towards physician. Appropriate measure?
- Have a chaperone join them

36. Cholera toxin catalyzes transfer of ADP-ribose to an arginine residue in stimulatory G protein resulting in inhibition of GTPase activity. Which increases in cells as a result?
- Concentration of cAMP

37. 8-year-old boy with pain on back and head since he fell off swing. Tender 2.5cm swollen mass over right occiput. CT shows osteolytic and soft-tissue mass in skull with
inward displacement of dura. Biopsy shows sheet-like infiltrate of pale eosinophilic cells with bean-shaped nuclei. Cells positive for CD1a. Electron microscopy of cells shows
Birbeck granules. Abnormal cell type?
- Langerhans cells

38. 60-year-old man 1 day of fever, chills, confusion and memory loss. Returned from Gulf coast where he walked barefoot. Hx of severe ci rrhosis and portal hypertension. T
39C (102.2 F), RR 22, bp 90/48. Physical shows early blister formation on right lower extremity. Blood culture: gram-negative, lactose-fermenting organism. Bug?
- Vibrio vulnificus

39. 20-year-old woman at 27 weeks' gestation is admitted to the hospital because of a 12-hour history of intense uterine contractions occurring every 8 minutes. Her
membranes ruptured 32 hours ago. Her temperature is 39.1°C(102.4°F), and pulse is 115/min. Physical examination shows tenderness of the uterus. Pelvic examination shows
a closed cervix that is not effaced. The fetal heart rate is 210/min. Which of the following is the primary stimulus for her uterine muscle contractions?
- Inflamed maternal decidua release of prostaglandin

40. Child with XXY karyotype, genetic studies showed he received the extra "x" from his father. An error of chromosome segregation occurred during anaphase at which of the
following stages of spermatogenesis in the patient's father?
- Primary spermatocyte

41. 10-year-old boy with 4 days nosebleeds and easy bruising. Three weeks ago, upper respiratory tract infection. PE ecchymoses on upper and lower extremities. Labs shows
hemoglobin and leukocyte count normal, and decreased platelet count. Bone marrow smear shows increased megakaryocytes. Mechanism of dz?
- Antibodies against glycoprotein (Gp) IIb/IIIa complex

42. 34-year-old man with a 3 month history of a progressive rash on his feet. Rash is not itchy or painful. A photograph of feet is shown. HIV+. In addition to HAART, which of
the following pharmacotherapy is most appropriate?
- Antineoplastic

43. 55-year-old man with elevated LDL cholesterol is prescribed lovastatin. This treatment would result in which adaptive responses at the cellular level?
- Increased transcription of HMG-CoA reductase

44. A new antiplatelet agent is developed for the prevention of recurrence of stroke. In a large randomized clinical trial with equal numbers of men and women, the rates of
stroke are lower in patients receiving the new agent than in patients receiving the standard treatment. Results are shown:
Recurrent Stroke Rates per 1000 Person-Years
Standard Treatment vs. New Antiplatelet Drug
Women .12 .04
Men .24 .08
Overall .18 .06
Based on these results, which of the following is the relative risk reduction in women?
- 67%




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