The NBME provides a lab values reference sheet during USMLE Step 1 and Step 2 CK. Mastering these normal ranges is essential for answering clinical vignette questions accurately and efficiently. This guide covers every panel tested — from complete blood count to arterial blood gases — so you walk into exam day with a solid command of what is normal, what is abnormal, and what it means clinically.
Whether you are preparing for Step 1 or Step 2 CK, bookmark this page as your go-to NBME practice test companion reference.
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.
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.
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).
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.
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.
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.
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.
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.
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.