The lab ranges nurses reach for most, condensed onto one printable page — CBC, electrolytes and renal, liver function, coagulation, ABG, and the critical values that need reporting straight away. Ranges vary by laboratory, so treat this as a study and orientation sheet and read real results against the report in front of you.
| Test | Normal range |
|---|---|
| WBC | 4,500–11,000 /µL |
| Haemoglobin (M / F) | 13.5–17.5 / 12.0–15.5 g/dL |
| Haematocrit (M / F) | 41–50% / 36–44% |
| Platelets | 150,000–400,000 /µL |
| MCV | 80–100 fL |
| Test | Normal range |
|---|---|
| Sodium | 135–145 mEq/L |
| Potassium | 3.5–5.0 mEq/L |
| Chloride | 98–106 mEq/L |
| Bicarbonate | 22–28 mEq/L |
| BUN | 10–20 mg/dL |
| Creatinine (M / F) | 0.6–1.2 / 0.5–1.1 mg/dL |
| Glucose (fasting) | 70–100 mg/dL |
| Calcium | 8.5–10.5 mg/dL |
| Magnesium | 1.5–2.5 mEq/L |
| Phosphate | 2.5–4.5 mg/dL |
| Test | Normal range |
|---|---|
| ALT / AST | 7–56 / 10–40 U/L |
| Alkaline phosphatase | 44–147 U/L |
| Total bilirubin | 0.1–1.2 mg/dL |
| Albumin | 3.5–5.0 g/dL |
| PT | 11–13.5 sec |
| INR | 0.8–1.1 (2.0–3.0 on warfarin) |
| aPTT | 30–40 sec |
PT/INR goes with warfarin; aPTT goes with heparin.
| Value | Normal |
|---|---|
| pH | 7.35–7.45 |
| PaCO₂ | 35–45 mmHg |
| PaO₂ | 80–100 mmHg |
| HCO₃⁻ | 22–26 mEq/L |
| SaO₂ | 95–100% |
ROME: Respiratory Opposite (pH and CO₂ move apart), Metabolic Equal (pH and HCO₃ move together).
| Test | Critical low | Critical high |
|---|---|---|
| Sodium | < 120 | > 160 mEq/L |
| Potassium | < 2.5 | > 6.5 mEq/L |
| Glucose | < 50 | > 400 mg/dL |
| Calcium | < 6.0 | > 13.0 mg/dL |
| Haemoglobin | < 7.0 g/dL | — |
| Platelets | < 50,000 /µL | > 1,000,000 /µL |
| INR | — | > 5.0 |
| pH | < 7.20 | > 7.60 |
Thresholds are set by each laboratory — follow your local critical value list. Look at the patient before the textbook: a high potassium in a well patient is often a haemolysed sample.
A normal serum potassium is 3.5 to 5.0 mEq/L. Below 3.5 is hypokalaemia and above 5.0 is hyperkalaemia. Because potassium drives cardiac conduction, a result outside the range should prompt a look at the ECG as well as the number.
Results far enough outside the normal range to suggest immediate risk, requiring escalation to the responsible clinician straight away. Typical adult examples include potassium below 2.5 or above 6.5 mEq/L, sodium below 120 or above 160, glucose below 50 or above 400 mg/dL, and haemoglobin below 7 g/dL. Each laboratory sets its own thresholds.
Each laboratory establishes its own ranges using its analysers, methods and local population, so small differences are normal. Always interpret a result against the range printed on that laboratory's own report.