100+ Free NBME CBSE Practice Questions

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A teenager has severe hypertension, hypokalemia, metabolic alkalosis, low renin, and low aldosterone. Symptoms improve with amiloride. Which molecular abnormality is most likely?

Loss of 11-beta-hydroxylase activity

Defective Na+-Cl- cotransporter in the distal tubule

Autoantibodies to the aldosterone receptor

Activating mutation of epithelial sodium channels

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Practice Questions100 questions

2026 Statistics

Key Facts: NBME CBSE Exam

200

Official Items

NBME Timing Chart

5h 15m

Exam Length

NBME Timing Chart

12-16%

Reproductive & Endocrine

NBME Content Outline

11-15%

Respiratory & Renal

NBME Content Outline

$61

Local Fee Through Jun 2026

NBME Fee Page

$151

Prometric Fee Through Jun 2026

NBME Fee Page

CBSE is a 200-item, 5-hour-15-minute NBME comprehensive basic science exam used by medical schools and programs to assess progress and readiness for USMLE Step 1. There is no universal passing score; interpretation depends on the sponsoring institution. Preparation should emphasize integrated mechanisms across pathology, physiology, pharmacology, microbiology, immunology, biochemistry, genetics, anatomy, behavioral science, and biostatistics.

Sample NBME CBSE Practice Questions

Try these sample questions to test your NBME CBSE exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1A newborn has truncus arteriosus, hypocalcemic tetany, recurrent viral infections, and an absent thymic shadow. Failure of migration of which embryologic cell population best explains the cardiovascular abnormality?

A.Neural crest cells

B.Paraxial mesoderm

C.Endoderm of the third pharyngeal pouch

D.Intermediate mesoderm

Explanation: Neural crest cells contribute to conotruncal septation of the cardiac outflow tract. Abnormal neural crest migration in 22q11.2 deletion can produce truncus arteriosus along with thymic and parathyroid hypoplasia.

2A fetus is noted on ultrasound to have persistent soft tissue webbing between the digits. Which cellular process normally removes this tissue during limb development?

A.Coagulative necrosis

B.Caspase-mediated apoptosis

C.Autophagy due to nutrient deprivation

D.Liquefactive necrosis

Explanation: Programmed cell death through caspase-mediated apoptosis sculpts the digits by removing interdigital tissue. The process preserves membrane integrity and avoids prominent inflammation.

3A 7-month-old infant has fasting hypoglycemia, lactic acidosis, hyperuricemia, and massive hepatomegaly. A liver biopsy shows excess glycogen with normal structure. Which enzyme is most likely deficient?

A.Muscle glycogen phosphorylase

B.Debranching enzyme

C.Glucose-6-phosphatase

D.Lysosomal alpha-1,4-glucosidase

Explanation: Glucose-6-phosphatase deficiency causes von Gierke disease. Inability to convert glucose-6-phosphate to free glucose leads to severe fasting hypoglycemia, lactic acidosis, hyperuricemia, and hepatomegaly from glycogen accumulation.

4A 3-year-old boy has developmental delay, self-injurious biting, orange crystals in his diaper, and choreoathetosis. Accumulation of which metabolite is most directly responsible for the crystal finding?

A.Orotic acid

B.Homogentisic acid

C.Uric acid

D.Phenylpyruvic acid

Explanation: Lesch-Nyhan syndrome is due to HGPRT deficiency, which impairs purine salvage and increases de novo purine synthesis. Excess purine degradation produces hyperuricemia and orange uric acid crystals.

5A sailor develops swollen gums, perifollicular hemorrhages, poor wound healing, and corkscrew hairs after months at sea. Which posttranslational modification is impaired?

A.Hydroxylation of proline and lysine residues

B.Gamma-carboxylation of glutamate residues

C.Glycosylation of lysosomal enzymes

D.Phosphorylation of serine residues

Explanation: Vitamin C is required for hydroxylation of proline and lysine during collagen synthesis. Deficiency weakens collagen triple helix stability, causing bleeding gums, petechiae, and impaired wound healing.

6A vegan patient develops macrocytic anemia, paresthesias, impaired vibration sense, and elevated methylmalonic acid. Which reaction is impaired by this vitamin deficiency?

A.Homocysteine to cystathionine

B.Methylmalonyl-CoA to succinyl-CoA

C.Pyruvate to oxaloacetate

D.Phenylalanine to tyrosine

Explanation: Vitamin B12 is a cofactor for methylmalonyl-CoA mutase, which converts methylmalonyl-CoA to succinyl-CoA. B12 deficiency causes elevated methylmalonic acid and neurologic dysfunction.

7A woman with exercise intolerance, lactic acidosis, and ragged-red fibers has three children. All inherited the same mitochondrial DNA mutation, but their symptoms vary widely. Which concept best explains this variable severity?

A.Genomic imprinting

B.Heteroplasmy

C.Loss of heterozygosity

D.Uniparental disomy

Explanation: Heteroplasmy is the presence of both normal and mutant mitochondrial DNA in cells. Different tissue burdens of mutant mitochondria cause variable expression among people with the same maternally inherited mutation.

8A man with early cataracts, frontal balding, distal muscle weakness, and difficulty releasing his grip has a daughter with more severe symptoms at a younger age. Which genetic mechanism explains this pattern?

A.Anticipation from trinucleotide repeat expansion

B.Balanced Robertsonian translocation

C.Mitochondrial heteroplasmy

D.New missense mutation with incomplete penetrance

Explanation: Myotonic dystrophy is caused by a trinucleotide repeat expansion and shows anticipation, with larger repeat sizes and earlier, more severe disease in later generations.

9A population study finds that 1 in 10,000 newborns has an autosomal recessive enzyme deficiency. Assuming Hardy-Weinberg equilibrium, what is the approximate carrier frequency?

A.1 in 100

B.1 in 50

C.1 in 25

D.1 in 10

Explanation: For an autosomal recessive disease, q squared is 1/10,000, so q is 1/100. The carrier frequency is approximately 2q, or 1/50.

10A teenager with sickle cell disease develops severe pain after dehydration during basketball practice. Which molecular event initiates the red cell sickling in deoxygenated blood?

A.Reduced ankyrin binding to spectrin

B.Polymerization of mutant hemoglobin

C.Failure of heme synthesis in erythroblasts

D.Oxidation of ferrous iron to ferric iron

Explanation: Deoxygenated hemoglobin S polymerizes because a valine substitution creates a hydrophobic interaction between hemoglobin molecules. Polymerization distorts red cells, promoting vaso-occlusion and hemolysis.

About the NBME CBSE Exam

The NBME Comprehensive Basic Science Examination is a secure, integrated achievement test covering material typically learned during basic science medical education, with somewhat greater emphasis on second-year content in traditional curricula. NBME states that CBSE reflects USMLE Step 1 content coverage and uses the same item formats. The official outline distributes foundational science across organ systems and includes medical knowledge, diagnosis, communication, and practice-based learning competencies.

Questions

200 scored questions

Time Limit

5 hours, 15 minutes, including a 15-minute optional break

Passing Score

Institution-specific; no universal national passing score

Exam Fee

$61 local / $151 Prometric through June 30, 2026 (NBME (National Board of Medical Examiners))

NBME CBSE Exam Content Outline

1-3%

Human Development

Normal age-related findings, embryology, development, and care of the well patient.

9-13%

Blood & Lymphoreticular/Immune Systems

Anemias, hemostasis, immune function, primary immunodeficiencies, hypersensitivity, and lymphoreticular pathology.

10-14%

Behavioral Health & Nervous Systems/Special Senses

Neuroanatomy, neurologic disease mechanisms, psychiatry, behavioral science, eye, ear, and related pharmacology.

8-12%

Musculoskeletal, Skin & Subcutaneous Tissue

Bone, muscle, joint, connective tissue, skin pathology, inflammation, and repair.

7-11%

Cardiovascular System

Cardiac physiology, vascular biology, congenital lesions, valvular disease, shock, and cardiovascular pharmacology.

11-15%

Respiratory & Renal/Urinary Systems

Pulmonary mechanics, oxygenation, renal transport, electrolyte disorders, acid-base physiology, and kidney pathology.

6-10%

Gastrointestinal System

GI physiology, malabsorption, liver disease, pancreas, nutrition, and GI infectious or immune mechanisms.

12-16%

Reproductive & Endocrine Systems

Hormone signaling, reproductive development, pregnancy, adrenal and thyroid physiology, diabetes, and endocrine tumors.

8-12%

Multisystem Processes & Disorders

Inflammation, shock, infection, neoplasia, immune complex disease, granulomatous disease, and systemic pathology.

4-6%

Biostatistics & Epidemiology/Population Health

Screening, diagnostic test performance, bias, study design, statistical interpretation, and population health.

6-9%

Social Sciences: Communication and Interpersonal Skills

Ethics, communication, professionalism, health behavior, and patient-centered decision-making.

How to Pass the NBME CBSE Exam

What You Need to Know

Passing score: Institution-specific; no universal national passing score
Exam length: 200 questions
Time limit: 5 hours, 15 minutes, including a 15-minute optional break
Exam fee: $61 local / $151 Prometric through June 30, 2026

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

NBME CBSE Study Tips from Top Performers

1Practice mixed organ-system questions rather than isolated facts; CBSE rewards transfer across disciplines.

2For every missed question, identify the mechanism: receptor, enzyme, immune pathway, anatomic lesion, hemodynamic change, or study-design rule.

3Use timed blocks to build the pacing needed for 200-item NBME-style testing.

4Track misses by the official system categories so remediation follows the NBME score-report language.

5Do not memorize recalled items; use original practice and official sample materials to learn the style ethically.

Frequently Asked Questions

What is the NBME CBSE?

The Comprehensive Basic Science Examination is an NBME comprehensive subject exam used by schools and programs to assess integrated basic science knowledge and readiness for USMLE Step 1.

How many questions are on CBSE?

The NBME timing chart lists Comprehensive Basic Science as a 200-item examination with a 5-hour, 15-minute exam length that includes a 15-minute optional break.

Does CBSE have a national passing score?

No universal passing score is published for CBSE. Schools and programs set their own score standards and use NBME reports to guide readiness decisions.

Is CBSE the same as USMLE Step 1?

No. CBSE is an NBME subject examination, but NBME states that it reflects Step 1 content coverage and uses the same item formats.

Can individuals buy the official CBSE as a practice test?

The official CBSE is ordered and administered by schools or sponsoring organizations in secure settings. Individuals typically use NBME self-assessments and other practice resources for independent preparation.

100+ Free NBME CBSE Practice Questions

NBME CBSE