Normal Lab Values Cheat Sheet for Nurses

Knowing your lab values cold is one of the most practical skills a bedside nurse can develop. When a result prints at 3 a.m. and the provider is asleep, it's your recognition — that potassium is critically high, that troponin is not a trace elevation — that determines whether the next thirty minutes go smoothly or catastrophically. This guide covers every major lab panel you'll encounter in clinical practice, with normal ranges, critical thresholds, and what each abnormality actually means for your patient.

If you want to sharpen your lab value recognition through daily practice, check out the Lab Values game at DailyNurseGames.com — a timed daily game that tests normal, critical low, and critical high thresholds and gets progressively harder as values approach the borderline.

Complete Blood Count (CBC)

The CBC is ordered on nearly every patient and gives you a snapshot of the blood's cellular components. Here are the values every nurse should know:

White Blood Cell Count (WBC)

Normal: 4,500 – 11,000 cells/mcL (4.5 – 11.0 × 10³/mcL)
Critical Low: < 2,000 cells/mcL — risk of life-threatening infection; neutropenic precautions
Critical High: > 30,000 cells/mcL — possible sepsis, leukemia, or severe systemic infection
Clinical note: Always look at the differential (neutrophils, bands, lymphocytes). A left shift (elevated bands) signals active bacterial infection even when total WBC is only mildly elevated.

Red Blood Cell Count (RBC)

Normal (male): 4.5 – 5.9 × 10⁶/mcL
Normal (female): 4.0 – 5.2 × 10⁶/mcL
Clinical note: RBC count is rarely acted on in isolation — use Hgb and Hct for clinical decision-making.

Hemoglobin (Hgb)

Normal (male): 13.5 – 17.5 g/dL
Normal (female): 12.0 – 15.5 g/dL
Critical Low: < 7.0 g/dL — typically triggers transfusion consideration; < 6.0 g/dL is a notify-now value at most institutions
Critical High: > 20.0 g/dL — hyperviscosity, polycythemia vera
Clinical note: Symptomatic patients (chest pain, dyspnea, altered mental status) may require transfusion at higher thresholds than 7.0 g/dL. Always treat the patient, not the number.

Hematocrit (Hct)

Normal (male): 41 – 53%
Normal (female): 36 – 46%
Critical Low: < 21% — consistent with critical Hgb threshold
Clinical note: Hct is approximately 3× the Hgb value. A quick mental check: Hgb 9 → Hct should be ~27.

Platelets

Normal: 150,000 – 400,000 cells/mcL
Critical Low: < 50,000 — increased bleeding risk; < 20,000 — spontaneous bleeding risk, notify provider immediately
Critical High: > 1,000,000 — thrombocytosis, clotting risk
Clinical note: Patients on heparin with falling platelets — think HIT (heparin-induced thrombocytopenia). A 50% drop from baseline is clinically significant even when the absolute count is still above 150,000.

Basic Metabolic Panel (BMP)

The BMP is your window into electrolyte balance, kidney function, and glucose homeostasis. These eight values come back together, and interpreting them as a set gives you the full picture.

Sodium (Na)

Normal: 136 – 145 mEq/L
Critical Low: < 120 mEq/L — seizure risk, cerebral edema
Critical High: > 160 mEq/L — hypernatremic encephalopathy
Clinical note: Hyponatremia is the most common electrolyte disorder in hospitalized patients. Correction must be gradual — correcting faster than 8–10 mEq/L per 24 hours risks osmotic demyelination syndrome (ODS).

Potassium (K)

Normal: 3.5 – 5.0 mEq/L
Critical Low: < 2.5 mEq/L — dysrhythmia risk, muscle weakness, respiratory failure
Critical High: > 6.5 mEq/L — peaked T waves, widened QRS, ventricular fibrillation
Clinical note: Potassium is the most dangerous electrolyte in clinical practice. Before giving IV potassium, always verify urine output is adequate (> 30 mL/hr) — you cannot correct hypokalemia in an anuric patient safely. IV potassium should never be pushed — it is always given as a diluted infusion.

Chloride (Cl)

Normal: 98 – 106 mEq/L
Critical Low: < 80 mEq/L — metabolic alkalosis, respiratory compensation
Critical High: > 115 mEq/L — metabolic acidosis
Clinical note: Chloride moves inversely with bicarbonate. Hyperchloremic metabolic acidosis is seen with aggressive normal saline resuscitation.

Carbon Dioxide / Bicarbonate (CO2 / HCO3)

Normal: 22 – 29 mEq/L
Critical Low: < 10 mEq/L — severe metabolic acidosis (DKA, sepsis, toxin ingestion)
Critical High: > 40 mEq/L — severe metabolic alkalosis

Blood Urea Nitrogen (BUN)

Normal: 8 – 20 mg/dL
Critical High: > 100 mg/dL — uremic symptoms possible; dialysis may be indicated
Clinical note: BUN is elevated in dehydration, GI bleeding, and high-protein states — not just renal failure. Always interpret with creatinine. A BUN:Creatinine ratio > 20:1 suggests pre-renal azotemia.

Creatinine (Cr)

Normal (male): 0.7 – 1.2 mg/dL
Normal (female): 0.5 – 1.0 mg/dL
Critical High: > 10.0 mg/dL (baseline dependent) — severe AKI or end-stage renal disease
Clinical note: A doubling of creatinine from baseline is clinically significant even if the absolute value is "normal." A patient whose baseline is 0.6 mg/dL with a current value of 1.2 mg/dL has had a 100% increase — that's stage 2 AKI by KDIGO criteria.

Glucose

Normal (fasting): 70 – 99 mg/dL
Critical Low: < 40 mg/dL — symptomatic hypoglycemia; immediate treatment required
Critical High: > 500 mg/dL — hyperosmolar hyperglycemic state (HHS) or severe DKA
Clinical note: In the hospital, most glucose protocols target 140–180 mg/dL for non-ICU patients. Any glucose below 70 mg/dL requires immediate intervention per most institutional protocols, regardless of symptoms.

Liver Function Tests (LFTs)

Alanine Aminotransferase (ALT)

Normal: 7 – 56 U/L
Elevated: > 3× upper limit of normal is clinically significant; > 1,000 U/L suggests acute hepatocellular injury (hepatitis, ischemic hepatitis, acetaminophen toxicity)
Clinical note: ALT is more liver-specific than AST. Markedly elevated ALT with a history of APAP use should prompt immediate toxicology evaluation.

Aspartate Aminotransferase (AST)

Normal: 10 – 40 U/L
Clinical note: AST is less specific than ALT — it's also elevated in muscle injury, MI, and hemolysis. An AST:ALT ratio > 2:1 is suggestive of alcoholic liver disease.

Alkaline Phosphatase (ALP)

Normal: 44 – 147 U/L (varies by age)
Elevated: Suggests cholestasis, biliary obstruction, or bone disease. Isolated ALP elevation with normal AST/ALT points away from hepatocellular injury.

Total Bilirubin

Normal: 0.2 – 1.2 mg/dL
Clinical note: Jaundice typically becomes visible when total bilirubin exceeds 2.5–3.0 mg/dL. Distinguish direct (conjugated, suggests hepatic/post-hepatic disease) from indirect (unconjugated, suggests hemolysis or Gilbert's syndrome).

Coagulation Studies

Prothrombin Time / INR (PT/INR)

Normal PT: 11 – 13 seconds
Normal INR: 0.8 – 1.1 (therapeutic range for anticoagulation: 2.0 – 3.0)
Critical High INR: > 5.0 — significant bleeding risk; provider notification required
Clinical note: INR > 1.5 is considered a coagulopathy risk for most procedures. Warfarin patients with INR > 4.0 and any bleeding symptom need urgent evaluation.

Partial Thromboplastin Time (PTT / aPTT)

Normal: 25 – 35 seconds
Therapeutic (heparin drip): 60 – 100 seconds (1.5–2.5× normal)
Critical High: > 120 seconds — bleeding risk

Fibrinogen

Normal: 200 – 400 mg/dL
Critical Low: < 100 mg/dL — DIC, massive hemorrhage, severe liver failure

Cardiac Markers

Troponin (Troponin I or Troponin T)

Normal: < 0.04 ng/mL (high-sensitivity troponin assays have lower thresholds — check your institution's reference range)
Elevated: Any value above the 99th percentile upper reference limit is abnormal
Clinical note: A rising or falling troponin pattern (serial troponins over 3–6 hours) is more diagnostically significant than a single value. Troponin can be elevated in non-ACS causes: PE, myocarditis, demand ischemia, sepsis, and renal failure. The pattern and clinical context matter.

B-Type Natriuretic Peptide (BNP)

Normal: < 100 pg/mL
Heart failure likely: > 400 pg/mL
Critical High: > 1,000 pg/mL — severe heart failure or decompensation
Clinical note: BNP rises when ventricular wall stress increases. Obesity lowers BNP; renal failure raises it. NT-proBNP has different reference ranges — do not interchange the two.

Arterial Blood Gas (ABG)

ABG interpretation is one of the most important skills in critical care nursing. A systematic approach — pH first, then primary disorder, then compensation — prevents errors.

pH

Normal: 7.35 – 7.45
Critical Low: < 7.20 — severe acidosis; cardiovascular instability
Critical High: > 7.60 — severe alkalosis; dysrhythmia and seizure risk

PaO2 (Partial Pressure of Oxygen)

Normal: 75 – 100 mmHg (on room air)
Hypoxemic: < 60 mmHg — supplemental oxygen indicated
Critical Low: < 40 mmHg — severe hypoxemia, immediate intervention required

PaCO2 (Partial Pressure of Carbon Dioxide)

Normal: 35 – 45 mmHg
Low: < 35 mmHg — respiratory alkalosis (hyperventilation)
High: > 45 mmHg — respiratory acidosis (hypoventilation, COPD, respiratory failure)
Critical High: > 70 mmHg — impending respiratory failure

HCO3 (Bicarbonate)

Normal: 22 – 26 mEq/L
Low: Metabolic acidosis (DKA, lactic acidosis, renal failure)
High: Metabolic alkalosis (prolonged vomiting, diuretic use, over-resuscitation with bicarb)

Quick ABG Interpretation Framework

Look at pH — acidotic (<7.35) or alkalotic (>7.45)?
Look at PaCO2 — if it matches the pH direction (high CO2 + low pH), it's a respiratory problem
Look at HCO3 — if it matches the pH direction (low bicarb + low pH), it's a metabolic problem
Is there compensation? Partial or full?
Look at PaO2 — is oxygenation adequate?

Mastering lab values takes repetition. Knowing the difference between a potassium of 5.8 and 6.5 — and what each demands of you — is the kind of reflexive knowledge that comes from practicing these thresholds regularly. The more automatic your recognition, the faster you act when it matters.