Reference — Lab
Critical Lab Values Reference
Critical (panic) values for electrolytes, hematology, coagulation, metabolic, cardiac, and ABG labs — thresholds, clinical risks, and required nursing actions.
Educational use only. Critical value thresholds and notification requirements vary by institution. Always use your facility's defined critical values and notification policy. Most facilities require provider notification within 30 minutes. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
Critical Value Notification Protocol
- Assess the patient immediately — determine urgency and safety
- Notify the primary provider or on-call provider using SBAR
- Receive and read back any new orders
- Implement ordered interventions
- Document: time value received, time provider notified, provider name, information communicated, response and orders received, action taken, patient status
Electrolytes
| Lab Test | Critical Low | Critical High | Risk | Required Action |
|---|---|---|---|---|
| Sodium (Na⁺) | < 120 mEq/L | > 160 mEq/L | Seizures, coma, herniation (low); cerebral dehydration, intracranial hemorrhage (high) | Notify provider; neurological assessment; seizure precautions; controlled correction ≤ 10–12 mEq/L per 24h |
| Potassium (K⁺) | < 2.5 mEq/L | > 6.5 mEq/L | Lethal dysrhythmia, paralysis (low); peaked T waves, VF, cardiac arrest (high) | Continuous ECG monitoring; notify provider immediately; have emergency medications ready; never IV push K⁺ |
| Calcium (Ca²⁺) | < 7.0 mg/dL | > 13.0 mg/dL | Tetany, laryngospasm, seizures, cardiac arrest (low); dysrhythmia, renal failure, coma (high) | IV calcium gluconate for critical low; saline hydration + furosemide for high; cardiac monitoring |
| Magnesium (Mg²⁺) | < 1.0 mEq/L | > 5.0 mEq/L | Seizures, dysrhythmias, torsades (low); respiratory depression, cardiac arrest (high) | IV MgSO4 for low; stop all Mg sources for high; calcium gluconate as antidote; monitor DTRs |
Hematology
| Lab Test | Critical Low | Critical High | Risk | Required Action |
|---|---|---|---|---|
| Hemoglobin | < 7 g/dL | > 20 g/dL | Tissue hypoxia, cardiovascular stress (low); hyperviscosity, thrombosis (high) | Assess for active bleeding; transfusion readiness; symptomatic assessment (pallor, tachycardia, dyspnea) |
| WBC | < 2,000 cells/μL | > 30,000 cells/μL | Severe infection risk (low); leukemia, sepsis, severe infection (high) | Reverse isolation for critically low; assess for infection signs; report fever ≥ 38°C (100.4°F) immediately |
| Platelets | < 20,000/μL | > 1,000,000/μL | Spontaneous bleeding risk (low); thrombosis risk (high) | Spontaneous bleeding precautions; hold all invasive procedures and injections; avoid antiplatelet drugs |
Coagulation
| Lab Test | Critical Low | Critical High | Risk | Required Action |
|---|---|---|---|---|
| INR (Warfarin patient) | — | > 3.5 | Major bleeding risk — intracranial hemorrhage, GI hemorrhage | Hold warfarin; notify provider; assess for active bleeding; prepare reversal (vitamin K, PCC); assess neuro status |
| aPTT (Heparin patient) | — | > 100 seconds | Major bleeding risk from excessive anticoagulation | Hold heparin infusion; notify provider; assess for bleeding; prepare protamine sulfate |
Metabolic / Renal
| Lab Test | Critical Low | Critical High | Risk | Required Action |
|---|---|---|---|---|
| Glucose | < 50 mg/dL | > 500 mg/dL | Seizures, loss of consciousness, death (low); DKA/HHS, cerebral edema (high) | Treat hypoglycemia immediately: D50W IV or glucagon IM; notify provider for both critical low and high |
| Creatinine | — | > 10 mg/dL | Severe renal failure — uremia, fluid overload, electrolyte crisis | Notify provider; assess fluid status; review medications for renal dose adjustment; consult nephrology |
Cardiac
| Lab Test | Critical Low | Critical High | Risk | Required Action |
|---|---|---|---|---|
| Troponin (any elevation) | — | Any value above the 99th percentile URL | Myocardial injury — ACS, PE, myocarditis, demand ischemia | Notify provider; serial ECGs; serial troponin; assess for chest pain, ischemic symptoms; cardiac monitoring |
Arterial Blood Gas
| Lab Test | Critical Low | Critical High | Risk | Required Action |
|---|---|---|---|---|
| pH | < 7.20 | > 7.60 | Cardiac dysrhythmia, hemodynamic instability, organ failure | Notify provider; assess respiratory status and airway; prepare for ventilatory support or bicarb administration |
| PaO₂ | < 50 mmHg | — | Severe hypoxia — tissue damage, cardiac arrest | Increase oxygen delivery immediately; notify provider; prepare for escalation (BiPAP, intubation) |
NCLEX Focus Points
Priority action for critical values: Assess the patient first, then notify the provider. On NCLEX, both steps are required — notifying without assessing, or assessing without notifying, are both incomplete answers.
Potassium is the most tested critical value: Hypokalemia → ECG first (U waves, flat T waves, prolonged QT). Hyperkalemia → ECG first (peaked T waves). Both: notify, monitor continuously, treat emergently.
Documentation timing matters: Facilities require notification within a defined timeframe (often 30 minutes). Document the exact time of notification — not just “provider notified.”
Glucose < 50 mg/dL = treat first: This is a medical emergency — give D50W or glucagon and THEN notify (simultaneously if possible). Do not wait for a provider order to treat severe symptomatic hypoglycemia.
Troponin elevations: Any troponin above the 99th percentile URL (upper reference limit) for that assay is considered critical — especially when trending upward over serial draws.
Related Resources
Standards & sources
Fact-checked Jun 21, 2026This page is written to align with Standard laboratory reference ranges · Clinical & Laboratory Standards Institute (CLSI). It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →