Every nurse ends up building a mental map of these numbers, usually the hard way — squinting at a results screen at 3am trying to remember whether a potassium of 5.4 is worth waking someone over. This page collects the adult reference ranges you'll meet most often, panel by panel, in both conventional and SI units, along with the critical values that need reporting immediately. One caveat before the tables: reference ranges are set by each individual laboratory, so treat these as a study and orientation guide, and read real results against the range printed on that lab's own report.
The most frequently ordered panel in nursing. It gives you oxygen-carrying capacity, immune status, and clotting potential in one draw.
| Test | Normal range | SI units |
|---|---|---|
| White blood cells (WBC) | 4,500–11,000 /µL | 4.5–11.0 × 10⁹/L |
| Red blood cells (RBC), male | 4.5–5.5 million/µL | 4.5–5.5 × 10¹²/L |
| Red blood cells (RBC), female | 4.0–4.9 million/µL | 4.0–4.9 × 10¹²/L |
| Haemoglobin (Hgb), male | 13.5–17.5 g/dL | 135–175 g/L |
| Haemoglobin (Hgb), female | 12.0–15.5 g/dL | 120–155 g/L |
| Haematocrit (Hct), male | 41–50% | 0.41–0.50 |
| Haematocrit (Hct), female | 36–44% | 0.36–0.44 |
| Platelets | 150,000–400,000 /µL | 150–400 × 10⁹/L |
| MCV | 80–100 fL | 80–100 fL |
A raised WBC usually points to infection, inflammation, or physiological stress (there's a plain-English explainer on what a high white blood cell count means for patients asking about their own results) — though remember it can also simply reflect steroids or a stress response, and an elderly or immunosuppressed patient can be seriously infected with a perfectly normal count. Low haemoglobin and haematocrit mean anaemia; low platelets mean bleeding risk, and that's the number to check before any procedure.
Electrolytes, kidney function, and glucose. The CMP adds liver tests to the same list.
| Test | Normal range | SI units |
|---|---|---|
| Sodium (Na⁺) | 135–145 mEq/L | 135–145 mmol/L |
| Potassium (K⁺) | 3.5–5.0 mEq/L | 3.5–5.0 mmol/L |
| Chloride (Cl⁻) | 98–106 mEq/L | 98–106 mmol/L |
| Bicarbonate (HCO₃⁻ / CO₂) | 22–28 mEq/L | 22–28 mmol/L |
| Blood urea nitrogen (BUN) | 10–20 mg/dL | 3.6–7.1 mmol/L |
| Creatinine, male | 0.6–1.2 mg/dL | 53–106 µmol/L |
| Creatinine, female | 0.5–1.1 mg/dL | 44–97 µmol/L |
| Glucose (fasting) | 70–100 mg/dL | 3.9–5.6 mmol/L |
| Calcium (total) | 8.5–10.5 mg/dL | 2.12–2.62 mmol/L |
| Magnesium | 1.5–2.5 mEq/L | 0.75–1.25 mmol/L |
| Phosphate | 2.5–4.5 mg/dL | 0.81–1.45 mmol/L |
Potassium is the one that bites. It governs cardiac conduction, and both ends of the range can throw life-threatening dysrhythmias — hyperkalaemia classically gives peaked T waves, hypokalaemia flattened T waves and U waves. If potassium is off, look at the ECG, not just the printout. Sodium tells a neurological story: low sodium swells cells and produces headache, confusion, and eventually seizures; high sodium dehydrates them, producing lethargy, irritability, and thirst.
BUN and creatinine together describe kidney function, and the ratio matters — a BUN rising faster than creatinine often points to dehydration rather than intrinsic kidney disease. If you need the actual clearance figure, the creatinine clearance calculator works it out from the creatinine here.
| Test | Normal range | SI units |
|---|---|---|
| ALT | 7–56 U/L | 7–56 U/L |
| AST | 10–40 U/L | 10–40 U/L |
| Alkaline phosphatase (ALP) | 44–147 U/L | 44–147 U/L |
| Total bilirubin | 0.1–1.2 mg/dL | 2–21 µmol/L |
| Albumin | 3.5–5.0 g/dL | 35–50 g/L |
| Total protein | 6.0–8.3 g/dL | 60–83 g/L |
ALT and AST rise when liver cells are damaged; ALP and bilirubin tend to rise with obstruction of the biliary tract. Albumin is worth a second glance for a reason that catches people out — it binds drugs, so a low albumin means more free drug circulating and a stronger effect from the same dose. It also drops in malnutrition and chronic illness, making it a rough marker of general condition.
| Test | Normal range | Notes |
|---|---|---|
| Prothrombin time (PT) | 11–13.5 seconds | Extrinsic pathway |
| INR | 0.8–1.1 | 2.0–3.0 therapeutic on warfarin |
| aPTT | 30–40 seconds | Intrinsic pathway; heparin monitoring |
| Fibrinogen | 200–400 mg/dL | 2.0–4.0 g/L |
The pairing worth memorising: PT/INR goes with warfarin, aPTT goes with heparin. An INR of 2.5 is alarming in someone not on anticoagulation and exactly on target for someone who is, which is a good reminder that a lab value only means something next to the patient's medication list.
| Test | Normal range |
|---|---|
| pH | 7.35–7.45 |
| PaCO₂ | 35–45 mmHg |
| PaO₂ | 80–100 mmHg |
| HCO₃⁻ | 22–26 mEq/L |
| SaO₂ | 95–100% |
| Base excess | −2 to +2 mEq/L |
The quick way through an ABG: look at the pH first to see which way it's gone, then check whether CO₂ or bicarbonate explains it — CO₂ moving the same direction as the disturbance means it's respiratory, bicarbonate means metabolic. Our ABG interpreter walks through the full sequence including compensation.
| Test | Desirable range | SI units |
|---|---|---|
| Total cholesterol | < 200 mg/dL | < 5.2 mmol/L |
| LDL cholesterol | < 100 mg/dL | < 2.6 mmol/L |
| HDL cholesterol | > 40 mg/dL (M) / > 50 (F) | > 1.0 / > 1.3 mmol/L |
| Triglycerides | < 150 mg/dL | < 1.7 mmol/L |
| HbA1c (normal) | < 5.7% | < 39 mmol/mol |
| HbA1c (prediabetes) | 5.7–6.4% | 39–47 mmol/mol |
| HbA1c (diabetes) | ≥ 6.5% | ≥ 48 mmol/mol |
HbA1c reflects roughly the previous three months of glucose control rather than this morning's reading, which is why it's the number used to diagnose and track diabetes. To move between mg/dL and mmol/L on a single glucose reading, the blood sugar converter does it instantly.
These are results that suggest immediate risk and need escalating to the responsible clinician straight away, not at the end of the round. The exact thresholds are set by each laboratory, so follow your local critical value list — but these are typical adult figures.
| Test | Critical low | Critical high |
|---|---|---|
| Sodium | < 120 mEq/L | > 160 mEq/L |
| Potassium | < 2.5 mEq/L | > 6.5 mEq/L |
| Glucose | < 50 mg/dL | > 400 mg/dL |
| Calcium | < 6.0 mg/dL | > 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 |
| PaO₂ | < 55 mmHg | — |
One practical habit worth building: when a critical value lands, look at the patient before you look anything else up. A potassium of 7.0 in someone alert and well is often a haemolysed sample and worth repeating; the same number in a breathless patient with a wide QRS is an emergency. Both need escalating — but they need different urgency in the next sixty seconds.
3.5 to 5.0 mEq/L. Below 3.5 is hypokalaemia, above 5.0 is hyperkalaemia. Potassium drives cardiac conduction, so a result outside the range should send you to the ECG as well as the number.
135 to 145 mEq/L. Low sodium swells cells and shows up neurologically — headache, confusion, and in severe cases seizures. High sodium dehydrates them, producing lethargy, irritability, and thirst.
Results far enough outside normal to suggest immediate risk, requiring escalation to the responsible clinician straight away. Typical examples: potassium below 2.5 or above 6.5 mEq/L, sodium below 120 or above 160, glucose below 50 or above 400 mg/dL, haemoglobin below 7 g/dL, platelets below 50,000/µL. Each laboratory sets its own thresholds, so follow your local list.
Each laboratory establishes its own ranges using its analysers, methods, and local population, so small differences are normal and expected. Always interpret a result against the range printed on that lab's own report rather than a general chart.