Reference ranges differ a little from one laboratory and one textbook to another. These are the ranges most often taught for adults. On the exam and in practice, read a value against the client: a hemoglobin of 10 means one thing after surgery and another in chronic kidney disease.
Electrolytes
| Test | Adult range | What it means for the nurse |
|---|
| Sodium | 135–145 mEq/L | Low: confusion, seizures. High: thirst, agitation. Correct slowly either way. |
| Potassium | 3.5–5.0 mEq/L | Either direction affects the heart. Check before loop diuretics and digoxin; watch the ECG. |
| Chloride | 98–106 mEq/L | Moves with sodium and with acid–base balance. |
| Calcium (total) | 8.5–10.5 mg/dL | Low: tingling, Chvostek and Trousseau signs, tetany. High: weakness, kidney stones. |
| Magnesium | 1.3–2.1 mEq/L | Low magnesium makes low potassium hard to correct. Watch reflexes during magnesium infusions. |
Kidney function and glucose
| Test | Adult range | What it means for the nurse |
|---|
| BUN | 10–20 mg/dL | Rises with dehydration, bleeding into the gut and kidney injury. |
| Creatinine | 0.6–1.2 mg/dL | The better marker of kidney function. Check before contrast and nephrotoxic drugs. |
| Glucose (fasting) | 70–99 mg/dL | Below 70: treat hypoglycemia first, then find the cause. |
| Hemoglobin A1c | Below 5.7% | Reflects about three months of glucose control. |
Blood counts
| Test | Adult range | What it means for the nurse |
|---|
| Hemoglobin | Women 12–16 g/dL · Men 14–18 g/dL | Falling values after surgery or with anticoagulants suggest bleeding. |
| Hematocrit | Women 37–47% · Men 42–52% | Rises with dehydration, falls with fluid overload and bleeding. |
| White blood cells | 5,000–10,000/mm³ | Low counts call for neutropenic precautions. |
| Platelets | 150,000–400,000/mm³ | Below about 50,000, bleeding risk rises: no injections where avoidable, soft toothbrush. |
Coagulation
| Test | Adult range | What it means for the nurse |
|---|
| PT / INR | INR about 0.8–1.1 | On warfarin the target is usually 2–3. Reversal: vitamin K. |
| aPTT | About 30–40 seconds | On heparin the target is usually 1.5–2.5 times control. Reversal: protamine. |
Arterial blood gases
| Test | Adult range | What it means for the nurse |
|---|
| pH | 7.35–7.45 | Below: acidosis. Above: alkalosis. |
| PaCO₂ | 35–45 mm Hg | The respiratory side. Moves opposite to pH in a respiratory problem. |
| HCO₃⁻ | 22–26 mEq/L | The metabolic side. Moves with pH in a metabolic problem. |
| PaO₂ | 80–100 mm Hg | Oxygenation, read with the SpO₂ and the client. |
Therapeutic drug levels
| Test | Adult range | What it means for the nurse |
|---|
| Digoxin | 0.5–2.0 ng/mL | Toxicity can occur within the range in older adults and with low potassium. |
| Lithium | 0.6–1.2 mEq/L | Narrow range. Dehydration and low sodium raise the level. |
How lab questions are asked
Most lab questions are not about the number itself. They ask which value needs action first, which finding goes with the value, or what to do before giving a medication. Learn the range, then learn the one sign you would see if the value were dangerous. Reduction of Risk Potential is the category where most of these appear.
For what each test measures and what results mean, the National Library of Medicine’s MedlinePlus lab test guide is free and written in plain language.