Know the danger zones

Critical lab values

The 43 tests in this reference that carry a commonly taught critical (panic) value, grouped by panel. Each row links to the full test page with reference ranges, causes, and nursing considerations. Critical results are reported to the provider immediately under your facility's policy - and every facility publishes its own thresholds, so treat these as teaching values.

Complete Blood Count (CBC)

5 tests with a critical value

Complete Blood Count (CBC): critical values and normal reference ranges for 5 tests
Test	Normal range	Critical value
Absolute Neutrophil Count (ANC)	2500-7000 cells/µL	< 500 cells/µL is severe neutropenia (high infection risk)
Hematocrit (Hct)	36-52 %	< 20% or > 60%
Hemoglobin (Hgb)	12-17.5 g/dL	< 7.0 g/dL (70 g/L) usually prompts transfusion consideration; > 20 g/dL
Platelet Count	150-400 10³/µL	< 50 × 10⁹/L (bleeding risk) - spontaneous bleeding risk rises sharply < 20; > 1,000
White Blood Cell Count (WBC)	4.5-11 10³/µL	< 2.0 or > 30.0 × 10⁹/L (severe neutropenia or marked leukocytosis)

Electrolytes & Minerals

8 tests with a critical value

Electrolytes & Minerals: critical values and normal reference ranges for 8 tests
Test	Normal range	Critical value
Bicarbonate (CO₂ content)	22-29 mEq/L	< 15 or > 40 mmol/L
Calcium, Ionized	4.6-5.3 mg/dL	< 3.2 or > 6.2 mg/dL
Calcium, Total (Ca²⁺)	8.6-10.2 mg/dL	< 6.0 or > 13.0 mg/dL
Chloride (Cl⁻)	98-106 mEq/L	< 80 or > 115 mmol/L
Magnesium (Mg²⁺)	1.6-2.6 mg/dL	< 1.0 or > 4.9 mg/dL
Phosphate (Phosphorus)	2.5-4.5 mg/dL	< 1.0 mg/dL
Potassium (K⁺)	3.5-5 mEq/L	< 2.5 or > 6.5 mmol/L (life-threatening arrhythmia risk)
Sodium (Na⁺)	135-145 mEq/L	< 120 or > 160 mmol/L (seizure and neurologic risk)

Kidney Function

3 tests with a critical value

Kidney Function: critical values and normal reference ranges for 3 tests
Test	Normal range	Critical value
Blood Urea Nitrogen (BUN)	7-20 mg/dL	> 100 mg/dL suggests serious renal impairment
Creatinine, Serum	0.6-1.3 mg/dL	> 4.0 mg/dL (or a rapid rise) indicates significant renal impairment
Estimated GFR (eGFR)	≥ 90 (normal kidney function) mL/min/1.73 m²	< 15 mL/min/1.73 m² indicates kidney failure

Glucose & Diabetes

2 tests with a critical value

Glucose & Diabetes: critical values and normal reference ranges for 2 tests
Test	Normal range	Critical value
Glucose, Fasting	70-99 mg/dL	< 50 or > 400 mg/dL
Glucose, Random	< 140 (non-fasting) mg/dL	< 50 or > 400 mg/dL

Liver Function (LFTs)

1 test with a critical value

Liver Function (LFTs): critical values and normal reference ranges for 1 test
Test	Normal range	Critical value
Bilirubin, Total	0.3-1.2 mg/dL	> 15 mg/dL in neonates (kernicterus risk)

Lipid Panel

1 test with a critical value

Lipid Panel: critical values and normal reference ranges for 1 test
Test	Normal range	Critical value
Triglycerides	< 150 normal mg/dL	> 500 mg/dL raises pancreatitis risk

Coagulation Studies

4 tests with a critical value

Coagulation Studies: critical values and normal reference ranges for 4 tests
Test	Normal range	Critical value
Activated Partial Thromboplastin Time (aPTT)	25-35 seconds	> 70 seconds (bleeding risk)
Fibrinogen	200-400 mg/dL	< 100 mg/dL (bleeding risk)
International Normalized Ratio (INR)	0.8-1.1 (off anticoagulation) ratio	> 5.0 (high spontaneous bleeding risk)
Prothrombin Time (PT)	11-13.5 seconds	> 30 seconds (marked bleeding risk)

Arterial Blood Gas (ABG)

5 tests with a critical value

Arterial Blood Gas (ABG): critical values and normal reference ranges for 5 tests
Test	Normal range	Critical value
Arterial pH	7.35-7.45 pH units	< 7.20 or > 7.60
HCO₃⁻ (Arterial Bicarbonate)	22-26 mEq/L	< 15 or > 40 mEq/L
PaCO₂ (Arterial CO₂)	35-45 mm Hg	< 20 or > 60 mm Hg
PaO₂ (Arterial O₂)	80-100 mm Hg	< 40 mm Hg (severe hypoxemia)
SaO₂ (Arterial Oxygen Saturation)	95-100 %	< 90% (hypoxemia)

Cardiac Markers

3 tests with a critical value

Cardiac Markers: critical values and normal reference ranges for 3 tests
Test	Normal range	Critical value
Creatine Kinase (CK)	30-200 U/L	Marked elevation (thousands) suggests rhabdomyolysis
Troponin I	< 0.04 (assay-dependent) ng/mL	Any elevation above the 99th percentile signals myocardial injury
Troponin T	< 0.01 (assay-dependent) ng/mL	Elevation above the assay's 99th percentile indicates myocardial injury

Therapeutic Drug Levels

9 tests with a critical value

Therapeutic Drug Levels: critical values and normal reference ranges for 9 tests
Test	Normal range	Critical value
Acetaminophen Level	10-30 (therapeutic) µg/mL	> 150 µg/mL at 4 h post-ingestion risks hepatotoxicity
Carbamazepine Level	4-12 µg/mL	> 12-15 µg/mL (ataxia, diplopia, drowsiness)
Digoxin Level	0.8-2 ng/mL	> 2.0 ng/mL is toxic (many target 0.5-0.9 in heart failure)
Lithium Level	0.6-1.2 mEq/L	> 1.5 mEq/L is toxic; > 2.0 is a medical emergency
Phenytoin Level	10-20 µg/mL	> 20 µg/mL (nystagmus, ataxia); > 30 confusion
Salicylate Level	15-30 (anti-inflammatory) mg/dL	> 40-50 mg/dL (tinnitus, tachypnea, acid-base disturbance)
Theophylline Level	10-20 µg/mL	> 20 µg/mL (nausea, tachycardia, seizures)
Valproic Acid Level	50-100 µg/mL	> 100-150 µg/mL (sedation, tremor)
Vancomycin Trough	10-20 µg/mL	> 20 µg/mL raises nephrotoxicity risk

Inflammatory & Other Chemistry

2 tests with a critical value

Inflammatory & Other Chemistry: critical values and normal reference ranges for 2 tests
Test	Normal range	Critical value
Lactate (Lactic Acid)	0.5-2.2 mmol/L	> 4 mmol/L signals significant hypoperfusion / sepsis
Osmolality, Serum	275-295 mOsm/kg	< 265 or > 320 mOsm/kg