NCLEX Lab Values Cheat Sheet: Every Critical Value You Must Know
Lab values are a fundamental part of nursing practice, and they're a favorite topic on the NCLEX. You need to know not just the normal ranges, but also what to do when a value is abnormal. This cheat sheet covers every critical lab value you need to know for the NCLEX, organized by category for easy reference.
Electrolytes
| Lab | Normal Range | Critical Value | Nursing Action |
|---|---|---|---|
| Sodium (Na+) | 135-145 mEq/L | <120 or >155 mEq/L | Low (Hyponatremia): Neurological changes (confusion, seizures). Monitor neuro status, restrict fluids if indicated. High (Hypernatremia): Thirst, agitation. Administer hypotonic fluids slowly. |
| Potassium (K+) | 3.5-5.0 mEq/L | <3.0 or >6.0 mEq/L | Low (Hypokalemia): Muscle weakness, cardiac arrhythmias. Administer potassium supplements, monitor ECG. High (Hyperkalemia): Cardiac arrest risk! Hold potassium, administer calcium gluconate, insulin+glucose, kayexalate. Monitor ECG. |
| Calcium (Ca2+) | 8.5-10.5 mg/dL | <6.5 or >13 mg/dL | Low (Hypocalcemia): Chvostek's/Trousseau's signs, tetany. Administer calcium supplements, seizure precautions. High (Hypercalcemia): "Stones, bones, groans, psychiatric overtones." Hydrate, administer loop diuretics. |
| Magnesium (Mg2+) | 1.5-2.5 mEq/L | <1.0 or >4.0 mEq/L | Low (Hypomagnesemia): Similar to hypocalcemia. Administer magnesium supplements. High (Hypermagnesemia): Loss of deep tendon reflexes, respiratory depression. Hold magnesium, administer calcium gluconate. |
Complete Blood Count (CBC)
| Lab | Normal Range | Critical Value | Nursing Action |
|---|---|---|---|
| Hemoglobin (Hgb) | M: 13.5-17.5 g/dL F: 12.0-15.5 g/dL |
<7.0 g/dL | Assess for anemia symptoms (fatigue, pallor). Prepare for possible blood transfusion. |
| Hematocrit (Hct) | M: 41-53% F: 36-46% |
<21% or >60% | Low: Anemia. High: Polycythemia, dehydration. |
| White Blood Cells (WBC) | 5,000-10,000/mm³ | <2,000 or >30,000/mm³ | Low: Neutropenia (infection risk). Implement neutropenic precautions. High: Infection, inflammation, leukemia. |
| Platelets | 150,000-400,000/mm³ | <20,000/mm³ | High risk of bleeding. Implement bleeding precautions (soft toothbrush, electric razor, avoid IM injections). |
Coagulation Studies
| Lab | Normal Range | Critical Value | Nursing Action |
|---|---|---|---|
| Prothrombin Time (PT) | 11-13.5 seconds | >20 seconds | Monitor for bleeding. Often used to monitor warfarin therapy. |
| International Normalized Ratio (INR) | 0.8-1.2 | >3.0-4.5 (therapeutic for warfarin) | Therapeutic range for warfarin is usually 2.0-3.0 (2.5-3.5 for mechanical heart valves). >5.0 = high bleeding risk. |
| Partial Thromboplastin Time (PTT) | 25-35 seconds | >70 seconds | Monitor for bleeding. Used to monitor heparin therapy. |
Arterial Blood Gases (ABGs)
Normal Values: pH: 7.35-7.45 | PaCO2: 35-45 mmHg | HCO3: 22-26 mEq/L | PaO2: 80-100 mmHg
Step-by-Step Interpretation:
- Look at pH: <7.35 = acidosis, >7.45 = alkalosis
- Look at PaCO2: >45 = respiratory acidosis, <35 = respiratory alkalosis
- Look at HCO3: >26 = metabolic alkalosis, <22 = metabolic acidosis
- Determine if compensation is present: If pH is abnormal but moving toward normal, it's compensated.
How to Use This Cheat Sheet
Memorize the normal ranges and critical values for the most common labs. For more detailed information on specific lab values and their clinical significance, check out our comprehensive NCLEX Lab Values Guide.
The best way to learn lab values is to see them in context. On NCLEX PrePro, we incorporate lab values into our practice questions so you can learn how to interpret them in real clinical scenarios.
Ready to master lab values for the NCLEX? Take a free practice test and see how our questions can help you prepare. Or, get lifetime access to our entire platform for just $29.