LabVals

Know the danger zones

Critical and threshold lab values

The 43 tests in this reference that carry a commonly taught threshold, grouped by panel. 25 of them are true critical (panic) values - results reported to the provider immediately under your facility's policy. The other 18 are labelled for what they actually state: a staging boundary, a drug toxicity level, a marker of injury or downstream risk, or simply a threshold where the taught wording does not settle which. Each row links to the full test page with reference ranges, causes, and nursing considerations, and every facility publishes its own thresholds, so treat these as teaching values.

Complete Blood Count (CBC)

5 tests with a taught threshold

Complete Blood Count (CBC): taught thresholds, the kind of threshold each one states, and normal reference ranges for 5 tests
TestNormal rangeThresholdKind
Absolute Neutrophil Count (ANC)2500-7000 cells/µL< 500 cells/µL is severe neutropenia (high infection risk)Threshold
Hematocrit (Hct)36-52 %< 20% or > 60%Critical value
Hemoglobin (Hgb)12-17.5 g/dL< 7.0 g/dL (70 g/L) usually prompts transfusion consideration; > 20 g/dLCritical value
Platelet Count150-400 10³/µL< 50 × 10⁹/L (bleeding risk) - spontaneous bleeding risk rises sharply < 20; > 1,000Critical value
White Blood Cell Count (WBC)4.5-11 10³/µL< 2.0 or > 30.0 × 10⁹/L (severe leukopenia or marked leukocytosis)Critical value

Electrolytes & Minerals

8 tests with a taught threshold

Electrolytes & Minerals: taught thresholds, the kind of threshold each one states, and normal reference ranges for 8 tests
TestNormal rangeThresholdKind
Bicarbonate (CO₂ content)22-29 mEq/L< 15 or > 40 mmol/LCritical value
Calcium, Ionized4.6-5.3 mg/dL< 3.2 or > 6.2 mg/dLCritical value
Calcium, Total (Ca²⁺)8.6-10.2 mg/dL< 6.0 or > 13.0 mg/dLCritical value
Chloride (Cl⁻)98-106 mEq/L< 80 or > 115 mmol/LCritical value
Magnesium (Mg²⁺)1.6-2.6 mg/dL< 1.0 or > 4.9 mg/dLCritical value
Phosphate (Phosphorus)2.5-4.5 mg/dL< 1.0 mg/dLCritical value
Potassium (K⁺)3.5-5 mEq/L< 2.5 or > 6.5 mmol/L (life-threatening arrhythmia risk)Critical value
Sodium (Na⁺)135-145 mEq/L< 120 or > 160 mmol/L (seizure and neurologic risk)Critical value

Kidney Function

3 tests with a taught threshold

Kidney Function: taught thresholds, the kind of threshold each one states, and normal reference ranges for 3 tests
TestNormal rangeThresholdKind
Blood Urea Nitrogen (BUN)7-20 mg/dL> 100 mg/dL suggests serious renal impairmentThreshold
Creatinine, Serum0.6-1.3 mg/dL> 4.0 mg/dL (or a rapid rise) indicates significant renal impairmentThreshold
Estimated GFR (eGFR)≥ 90 (normal kidney function) mL/min/1.73 m²< 15 mL/min/1.73 m² indicates kidney failureStaging threshold

Glucose & Diabetes

2 tests with a taught threshold

Glucose & Diabetes: taught thresholds, the kind of threshold each one states, and normal reference ranges for 2 tests
TestNormal rangeThresholdKind
Glucose, Fasting70-99 mg/dL< 50 or > 400 mg/dLCritical value
Glucose, Random< 140 (non-fasting) mg/dL< 50 or > 400 mg/dLCritical value

Liver Function (LFTs)

1 test with a taught threshold

Liver Function (LFTs): taught thresholds, the kind of threshold each one states, and normal reference ranges for 1 test
TestNormal rangeThresholdKind
Bilirubin, Total0.3-1.2 mg/dL> 15 mg/dL in neonates (kernicterus risk)Critical value

Lipid Panel

1 test with a taught threshold

Lipid Panel: taught thresholds, the kind of threshold each one states, and normal reference ranges for 1 test
TestNormal rangeThresholdKind
Triglycerides< 150 normal mg/dL> 500 mg/dL raises pancreatitis riskRisk threshold

Coagulation Studies

4 tests with a taught threshold

Coagulation Studies: taught thresholds, the kind of threshold each one states, and normal reference ranges for 4 tests
TestNormal rangeThresholdKind
Activated Partial Thromboplastin Time (aPTT)25-35 seconds> 70 seconds (bleeding risk)Critical value
Fibrinogen200-400 mg/dL< 100 mg/dL (bleeding risk)Critical value
International Normalized Ratio (INR)0.8-1.1 (off anticoagulation) ratio> 5.0 (high spontaneous bleeding risk)Critical value
Prothrombin Time (PT)11-13.5 seconds> 30 seconds (marked bleeding risk)Critical value

Arterial Blood Gas (ABG)

5 tests with a taught threshold

Arterial Blood Gas (ABG): taught thresholds, the kind of threshold each one states, and normal reference ranges for 5 tests
TestNormal rangeThresholdKind
Arterial pH7.35-7.45 pH units< 7.20 or > 7.60Critical value
HCO₃⁻ (Arterial Bicarbonate)22-26 mEq/L< 15 or > 40 mEq/LCritical value
PaCO₂ (Arterial CO₂)35-45 mm Hg< 20 or > 60 mm HgCritical value
PaO₂ (Arterial O₂)80-100 mm Hg< 40 mm Hg (severe hypoxemia)Critical value
SaO₂ (Arterial Oxygen Saturation)95-100 %< 90% (hypoxemia)Critical value

Cardiac Markers

3 tests with a taught threshold

Cardiac Markers: taught thresholds, the kind of threshold each one states, and normal reference ranges for 3 tests
TestNormal rangeThresholdKind
Creatine Kinase (CK)30-200 U/LMarked elevation (thousands) suggests rhabdomyolysisThreshold
Troponin I< 0.04 (assay-dependent) ng/mLAny elevation above the 99th percentile signals myocardial injuryInjury threshold
Troponin T< 0.01 (assay-dependent) ng/mLElevation above the assay's 99th percentile indicates myocardial injuryInjury threshold

Therapeutic Drug Levels

9 tests with a taught threshold

Therapeutic Drug Levels: taught thresholds, the kind of threshold each one states, and normal reference ranges for 9 tests
TestNormal rangeThresholdKind
Acetaminophen Level10-30 (therapeutic) µg/mL> 150 µg/mL at 4 h post-ingestion risks hepatotoxicityToxicity threshold
Carbamazepine Level4-12 µg/mL> 12-15 µg/mL (ataxia, diplopia, drowsiness)Toxicity threshold
Digoxin Level0.8-2 ng/mL> 2.0 ng/mL is toxic (many target 0.5-0.9 in heart failure)Toxicity threshold
Lithium Level0.6-1.2 mEq/L> 1.5 mEq/L is toxic; > 2.0 is a medical emergencyToxicity threshold
Phenytoin Level10-20 µg/mL> 20 µg/mL (nystagmus, ataxia); > 30 confusionToxicity threshold
Salicylate Level15-30 (anti-inflammatory) mg/dL> 40-50 mg/dL (tinnitus, tachypnea, acid-base disturbance)Toxicity threshold
Theophylline Level10-20 µg/mL> 20 µg/mL (nausea, tachycardia, seizures)Toxicity threshold
Valproic Acid Level50-100 µg/mL> 100-150 µg/mL (sedation, tremor)Toxicity threshold
Vancomycin Trough10-20 µg/mL> 20 µg/mL raises nephrotoxicity riskToxicity threshold

Inflammatory & Other Chemistry

2 tests with a taught threshold

Inflammatory & Other Chemistry: taught thresholds, the kind of threshold each one states, and normal reference ranges for 2 tests
TestNormal rangeThresholdKind
Lactate (Lactic Acid)0.5-2.2 mmol/L> 4 mmol/L signals significant hypoperfusion / sepsisThreshold
Osmolality, Serum275-295 mOsm/kg< 265 or > 320 mOsm/kgCritical value