NCLEX Lab Values to Know: A Nursing Cheat Sheet
A printable NCLEX-RN lab values cheat sheet — normal adult ranges for electrolytes, renal, hematology, ABGs, and therapeutic drug levels, with the nursing action each one points to.
By the Clesial Editorial Team
Updated June 30, 2026 · 6 min read
Lab values show up all over the NCLEX-RN, and the exam rarely asks you to just recall a number. It asks what you'd do about it. This cheat sheet pairs the normal adult ranges you need to memorize with the nursing action each one points to.
Read this first
These are typical adult reference ranges; exact cutoffs vary by lab and source, so always defer to your facility's values and your current review materials. Use this to build pattern recognition, not as a clinical reference.
Electrolytes
| Test | Normal (adult) | What the NCLEX wants |
|---|---|---|
| Sodium (Na+) | 135-145 mEq/L | Low → confusion/seizures; high → thirst, dry mucosa. Watch neuro changes. |
| Potassium (K+) | 3.5-5.0 mEq/L | Narrow + lethal. Both low and high cause dysrhythmias — get an ECG, never IV push K+. |
| Calcium (Ca2+) | 9.0-10.5 mg/dL | Low → tetany, Chvostek/Trousseau; high → weakness, stones. Inverse with phosphorus. |
| Magnesium (Mg2+) | 1.5-2.5 mg/dL | Low → torsades, hyperreflexia; high → loss of reflexes (check patellar reflex on Mg drips). |
| Phosphorus | 3.0-4.5 mg/dL | Moves inverse to calcium. Watch in renal failure and refeeding. |
| Chloride (Cl-) | 98-106 mEq/L | Tracks sodium and acid-base; rarely the standalone answer. |
Renal & metabolic
| Test | Normal (adult) | What the NCLEX wants |
|---|---|---|
| BUN | 10-20 mg/dL | Rises with dehydration, GI bleed, high protein, kidney injury. |
| Creatinine | 0.6-1.2 mg/dL | Best single kidney marker. A rise = hold nephrotoxins, recheck dosing. |
| Fasting glucose | 70-100 mg/dL | < 70 → treat the low first (15 g fast carbs). Hypo beats hyper for urgency. |
| HbA1c | < 5.7% (goal < 7% if diabetic) | Reflects ~3-month control, not the moment. |
Hematology & coagulation
| Test | Normal (adult) | What the NCLEX wants |
|---|---|---|
| Hemoglobin (Hgb) | Men 14-18 / Women 12-16 g/dL | Low → fatigue, pallor, tachycardia; assess for bleeding. |
| Hematocrit (Hct) | Men 42-52% / Women 37-47% | Roughly 3× the hemoglobin. |
| WBC | 5,000-10,000 /mm3 | Low → neutropenic precautions; high → infection. A low WBC on chemo is the emergency. |
| Platelets | 150,000-400,000 /mm3 | < 50,000 → bleeding precautions; < 20,000 → spontaneous bleeding risk. |
| INR | 0.8-1.1 (warfarin goal 2-3) | High → hold warfarin, bleeding risk; vitamin K is the antidote. |
| aPTT | 30-40 sec (heparin goal 1.5-2.5× control) | High → hold heparin; protamine sulfate is the antidote. |
Arterial blood gases (ABGs)
Read ABGs in order: pH first (acidosis or alkalosis?), then match the cause. If PaCO2 moves opposite the pH, it's respiratory; if HCO3 moves with the pH, it's metabolic.
| Test | Normal (adult) | What the NCLEX wants |
|---|---|---|
| pH | 7.35-7.45 | < 7.35 acidosis, > 7.45 alkalosis. Anchor every ABG here first. |
| PaCO2 | 35-45 mmHg | The respiratory number. Moves opposite pH in respiratory problems. |
| HCO3- | 22-26 mEq/L | The metabolic number. Moves with pH in metabolic problems. |
| PaO2 | 80-100 mmHg | Oxygenation. < 60 is the danger zone. |
Therapeutic drug levels
These drugs have a narrow window, so the exam loves them. Know the ceiling and the first signs of toxicity.
| Test | Normal (adult) | What the NCLEX wants |
|---|---|---|
| Digoxin | 0.5-2.0 ng/mL | Toxic > 2. Hold for apical HR < 60; nausea + visual halos = toxicity. |
| Lithium | 0.6-1.2 mEq/L | Toxic > 1.5. Low sodium/dehydration raises the level. Tremor, vomiting, confusion. |
| Phenytoin | 10-20 mcg/mL | Toxic → nystagmus, ataxia, slurred speech. |
| Theophylline | 10-20 mcg/mL | Narrow window; watch for tachycardia, nausea, seizures. |
| Vancomycin (trough) | 10-20 mcg/mL | Monitor trough + renal function; watch for ototoxicity. |
How the NCLEX actually tests lab values
- It wants the action, not the number.Expect "which finding do you report first?" — pick the value that signals the biggest immediate risk (potassium and pH are common answers).
- Treat the low glucose before the high. Hypoglycemia is the faster killer.
- A new or rising creatinine should make you hold nephrotoxic drugs and re-check dosing.
- For drug levels, link the toxicity sign to the drug (digoxin → halos, lithium → tremor, phenytoin → nystagmus).
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Bottom line
Memorize the ranges, but study the action beside each one. The exam tests whether a value should make you intervene, report, or hold a drug, not whether you can recite a number.
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