Are the NBME lab values the same for Step 1 and Step 2 CK?

Yes. The NBME provides the same standardized reference sheet for both USMLE Step 1 and Step 2 CK. The panels include CBC, comprehensive metabolic panel, liver function tests, cardiac markers, thyroid studies, coagulation studies, and arterial blood gas values. Memorizing these ranges before either exam gives you a significant time advantage since you will not need to consult the reference sheet for routine values.

Which lab values are most commonly tested on USMLE Step 1?

The highest-yield values for Step 1 are hemoglobin and hematocrit (anemia and polycythemia), serum electrolytes (especially sodium, potassium, and bicarbonate for acid-base disorders), creatinine and BUN (renal function), and arterial blood gas parameters for acid-base interpretation. Thyroid function — particularly TSH — and liver enzymes are also frequently tested in the context of biochemistry and pathophysiology questions.

What is the normal anion gap, and when does it become elevated?

The normal anion gap is 8-12 mEq/L, calculated as sodium minus the sum of chloride and bicarbonate. An elevated anion gap above 12 mEq/L indicates the presence of an unmeasured anion and points to causes summarized by the MUDPILES mnemonic: Methanol, Uremia, Diabetic ketoacidosis, Propylene glycol or Paraldehyde, Isoniazid or Iron, Lactic acidosis, Ethylene glycol, and Salicylates. A normal anion gap metabolic acidosis suggests GI bicarbonate loss (diarrhea) or renal tubular acidosis.

How do I interpret a troponin result on USMLE vignettes?

On USMLE exams, a Troponin I above 0.1 ng/mL is abnormal. However, the pattern of troponin change is as important as the absolute value. Troponin begins rising 3-6 hours after myocardial injury, peaks at 12-24 hours, and can remain elevated for up to 10-14 days. A single elevated troponin without a clinical history of chest pain could represent demand ischemia (Type 2 MI), myocarditis, or pulmonary embolism rather than acute STEMI. Always interpret troponin in context.

What is the difference between PT and PTT on the NBME reference sheet?

Prothrombin time (PT, normal 11-15 seconds) measures the extrinsic coagulation pathway involving factors II, V, VII, and X. Warfarin, vitamin K deficiency, and liver disease predominantly prolong PT. Partial thromboplastin time (PTT, normal 25-40 seconds) measures the intrinsic pathway involving factors VIII, IX, XI, and XII. Heparin therapy and hemophilia A (factor VIII deficiency) or hemophilia B (factor IX deficiency) prolong PTT. Both PT and PTT are prolonged in DIC and severe liver disease.

Is the NBME lab values reference sheet available during all USMLE steps?

The laboratory reference sheet is provided during USMLE Step 1 and Step 2 CK. It is accessible through the exam interface and lists normal ranges for all major panels. For Step 3, a similar resource is available. The purpose of providing the sheet is to allow candidates to focus on clinical reasoning rather than rote memorization of exact cutoffs — however, knowing the values by heart prevents the time cost of switching to the reference screen during time-sensitive blocks.

How should I study NBME lab values to maximize my score?

The most effective strategy is to learn lab values in clinical context rather than as a list. Practice interpreting CBC findings in anemia workups, metabolic panels in acid-base disorders, and liver function patterns in hepatitis versus cholestasis. Use NBME-style practice questions that present abnormal values in vignettes and require you to identify the diagnosis. Reviewing the values daily for two weeks before the exam ensures they become automatic, freeing cognitive resources for the harder reasoning steps the USMLE actually tests.

NBME Lab Values 2026 — Medical Reference Ranges for USMLE Prep

NBME lab values 2026: complete reference guide to laboratory normal values tested on USMLE Step 1 and Step 2 CK covering blood counts, metabolic panels, cardiac markers, and ABG interpretation.

NBME - National Board of Medical ExaminersApr 22, 20267 min read

NBME Lab Values 2026 — Medical Reference Ranges for USMLE Prep

Why NBME Lab Values Matter on the USMLE

The USMLE is a clinically oriented exam. Every Step 1 and Step 2 CK vignette places a patient in a scenario where laboratory data drives diagnosis, management, or both. The NBME supplies a standardized lab values sheet precisely because test-makers expect you to apply these numbers — not memorize them from scratch on exam day.

That said, relying entirely on the reference sheet is a trap. High-yield questions are written so that you must recognize a value as abnormal within seconds, then pivot immediately to a clinical interpretation. Candidates who have internalized these ranges move faster and make fewer errors under time pressure.

The panels below match the NBME reference sheet format used for current USMLE administrations. Values are presented with the units and sex-based distinctions exactly as they appear on the official sheet.

Why Nbme Lab Values Matter on the Usmle - NBME - National Board of Medical Examiners certification study resource

NBME Lab Values Quick Reference

Complete Blood Count (CBC)CBC

Step 1Step 2 CKHigh Yield

WBC: 4.5-11.0 x10^3/mcL
RBC (Male): 4.5-5.9 x10^6/mcL
RBC (Female): 4.1-5.3 x10^6/mcL
Hemoglobin (Male): 13.5-17.5 g/dL
Hemoglobin (Female): 12.0-16.0 g/dL
Hematocrit (Male): 41-53%
Hematocrit (Female): 36-46%
MCV: 80-100 fL
Platelets: 150-400 x10^3/mcL

Basic Metabolic Panel (BMP)BMP

Step 1Step 2 CKHigh Yield

Sodium (Na+): 136-145 mEq/L
Potassium (K+): 3.5-5.0 mEq/L
Chloride (Cl-): 98-106 mEq/L
Bicarbonate (HCO3-): 22-26 mEq/L
BUN: 7-20 mg/dL
Creatinine: 0.6-1.2 mg/dL
Glucose (fasting): 70-110 mg/dL
Calcium (Ca2+): 8.5-10.2 mg/dL

Liver Function and Cardiac MarkersLFT + Cardiac

Step 1Step 2 CK

AST: 10-40 U/L
ALT: 7-45 U/L
Alkaline Phosphatase: 45-115 U/L
Total Bilirubin: 0.1-1.0 mg/dL
Direct Bilirubin: 0.0-0.3 mg/dL
Albumin: 3.5-5.5 g/dL
Total Protein: 6.0-8.3 g/dL
Troponin I: <0.1 ng/mL
BNP: <100 pg/mL
CK-MB: 0-4% of total CK

Coagulation and ThyroidCoag + Thyroid

Step 1Step 2 CK

PT: 11-15 seconds
PTT: 25-40 seconds
INR: 0.8-1.2
TSH: 0.5-5.0 mIU/L
Free T4: 0.8-1.8 ng/dL
Free T3: 2.3-4.2 pg/mL

Arterial Blood Gas (ABG) Reference Values

The ABG panel is one of the most tested sections on Step 1 and Step 2 CK. You will need to recognize primary acid-base disorders and compensatory responses instantly.

pH: 7.35-7.45 — below 7.35 is acidosis; above 7.45 is alkalosis
PaCO2: 35-45 mmHg — the respiratory component; elevated in respiratory acidosis, decreased in respiratory alkalosis
PaO2: 75-100 mmHg — below 60 mmHg defines hypoxemia
HCO3-: 22-26 mEq/L — the metabolic component; decreased in metabolic acidosis, elevated in metabolic alkalosis
O2 Saturation: 95-100% — critical threshold at 90% (corresponds to PaO2 of ~60 mmHg on the oxyhemoglobin dissociation curve)

When analyzing an ABG on the exam, follow this sequence: check pH first, determine primary disorder, assess compensation, then calculate the anion gap if metabolic acidosis is present (normal anion gap = 8-12 mEq/L).

Nbme Lab Values Quick Reference - NBME - National Board of Medical Examiners certification study resource

Common Pitfalls When Interpreting NBME Lab Values

Understanding normal ranges is only half the battle. The USMLE is designed to test whether you can correctly apply those ranges in context. Below are the most frequently tested pitfalls that trip up even well-prepared candidates.

Ignoring the Direction of Change

Many vignettes do not ask whether a value is abnormal in isolation — they ask which direction it shifts in a specific disease. For example, both diarrhea (metabolic acidosis) and vomiting (metabolic alkalosis) alter HCO3-, but in opposite directions. Knowing the range is not enough; you must know what drives values up or down in common clinical presentations.

Forgetting Sex-Specific Hemoglobin Cutoffs

A hemoglobin of 12.5 g/dL is normal in a woman but anemia in a man. This distinction is explicitly tested. Always check patient sex before labeling any CBC value as normal or abnormal.

Misinterpreting Compensated vs. Uncompensated Disorders

A compensated respiratory acidosis will show elevated PaCO2 and elevated HCO3-, with a pH that may be close to — but not quite — normal. Candidates sometimes call this a mixed disorder when it is actually a primary problem with appropriate metabolic compensation.

Over-relying on a Single Marker

Troponin alone does not diagnose MI on the USMLE. Look for the clinical context: chest pain, ECG changes, and a rising-then-falling troponin trend together confirm the diagnosis. Similarly, an elevated AST alone does not tell you the organ of origin without the ALT ratio and alkaline phosphatase.

Missing the Reference Sheet Cutoffs for Creatinine

The NBME creatinine normal range tops out at 1.2 mg/dL. A value of 1.4 in a muscular male athlete may be physiologic in real life but is abnormal by NBME standards. Follow the reference sheet, not clinical intuition.

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NBME Lab Values — Frequently Asked Questions

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