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Normal lab values for nurses
Every range on this page is attributed to a named, dated source — and where authoritative sources genuinely disagree, we show you that instead of picking one and pretending.
Do you have to memorise these for the NCLEX?
Not the way most study guides imply. NCSBN, which writes the NCLEX, states:
“Beginning with the launch of the Next Generation NCLEX, items that contain a numeric laboratory value will include the corresponding normal reference range.”
— NCSBN, NCLEX Frequently Asked Questions, read 2026-09-03. The Next Generation NCLEX launched 1 April 2023.
So the exam gives you the range. What it does not give you is the judgement: which direction is dangerous, which result needs action before you finish reading the chart, and what the abnormality means for this patient. That is what to study, and it is what this page is organised around.
Why there is no single “normal range”
A reference interval is the middle 95% of results from a healthy reference population, measured on one laboratory's assay — so 5% of perfectly healthy people fall outside it by design, and different laboratories legitimately publish different ranges. Always interpret a result against the range printed on that patient's own report.
This is not a technicality. For adult male hematocrit, three authoritative sources give 42–50%, 40–55% and 37–48%. For arterial pH, the reference list used by one major medical certification board gives 7.38–7.44 where nursing teaching almost universally uses 7.35–7.45. Any page that prints one number without saying where it came from is hiding that from you.
Where these numbers come from
The ranges below are transcribed from the American Board of Internal Medicine’s Laboratory Test Reference Ranges, revised January 2026, read directly on 2026-09-03. We chose it because it is free, dated, versioned, internally consistent, and is an actual examination’s published reference list.
Its limit, stated plainly: it is a physician certification board’s list, not a nursing document and not NCSBN’s. NCSBN publishes no lab-value list at all. Where other authoritative sources differ from it, the row says so.
Reference intervals
These are laboratory reference intervals — derived from a healthy population on a particular assay, and therefore laboratory-specific.
Electrolytes
| Test | Common reference range | What it measures and why it matters |
|---|---|---|
| Sodium (Na⁺) | 136–145mEq/L | Sodium concentration in serum — in practice, the balance between sodium and water.Sodium disturbances present neurologically, not as a symptom you can see in the electrolyte panel: confusion, headache and seizures. How fast it changed matters more than the number itself. |
| Potassium (K⁺) | 3.5–5.0mEq/L | Serum potassium, the dominant intracellular cation.The narrowest therapeutic window on the panel. Both directions are cardiac emergencies, and IV potassium is never given as a push.Sources differ: Serum and plasma potassium differ by roughly 0.2–0.4 mmol/L, yet most laboratories publish one range for both. |
| Chloride (Cl⁻) | 98–106mEq/L | Serum chloride, the main extracellular anion.Read alongside sodium and bicarbonate — it is most useful for working out the type of acid–base disturbance, not on its own. |
| Calcium (Ca²⁺), total | 8.6–10.2mg/dL | Total serum calcium, most of which is bound to albumin.Total calcium tracks albumin, so a low albumin lowers total calcium without the ionised (active) calcium changing at all. |
| Magnesium (Mg²⁺) | 1.6–2.6mg/dL | Serum magnesium.Low magnesium makes low potassium refractory — potassium often will not correct until the magnesium is replaced. |
Complete blood count
| Test | Common reference range | What it measures and why it matters |
|---|---|---|
| Hemoglobin (Hgb) | Female 12–16 · Male 14–18g/dL | The oxygen-carrying protein in red cells.The number that decides whether tissue is being oxygenated. Sex-partitioned in every source.Sources differ: Sources differ on the male range: ABIM gives 14–18 g/dL, MedlinePlus 13–18. WHO's anaemia cut-offs are different again — and are adjusted for altitude and smoking. |
| Hematocrit (Hct) | Female 37–47 · Male 42–50% | The proportion of blood volume occupied by red cells.Roughly three times the hemoglobin in a stable patient — a pair that diverges is worth a second look.Sources differ: The clearest example on this page that no single normal range exists. For adult males, ABIM gives 42–50%, MedlinePlus 40–55% and StatPearls 37–48% — a 22-point spread at the top end across three authoritative sources. |
| White blood cell count (WBC) | 4,000–11,000/μL | Total circulating leukocytes.A rise suggests infection or inflammation; a fall means the patient may not be able to mount a response at all, which is the more dangerous direction.Sources differ: Reported in three different unit systems across sources — /μL, /mm³ and ×10⁹/L — which look like different numbers but are the same value. |
| Platelet count | 150,000–450,000/μL | Circulating platelets.Drives bleeding precautions. The threshold for concern is a facility policy, not a universal number.Sources differ: ABIM's upper limit is 450,000/μL; several nursing sources publish 400,000. |
Renal function
| Test | Common reference range | What it measures and why it matters |
|---|---|---|
| Blood urea nitrogen (BUN) | 8–20mg/dL | Nitrogen carried in urea, a protein breakdown product cleared by the kidney.Rises with dehydration, GI bleeding and high protein intake as well as with kidney disease — it is not a kidney-specific test. |
| Creatinine | Female 0.50–1.10 · Male 0.70–1.30mg/dL | A muscle breakdown product cleared almost entirely by the kidney.More specific for kidney function than BUN, but it depends on muscle mass — a frail older adult can have significant kidney impairment with a creatinine that still reads normal.Sources differ: MedlinePlus contradicts itself here: its basic-metabolic-panel article gives 0.8–1.2 mg/dL with no sex split, while its dedicated creatinine article gives female 0.5–0.95 and male 0.7–1.3. |
Liver function
| Test | Common reference range | What it measures and why it matters |
|---|---|---|
| Albumin | 3.5–5.5g/dL | The main protein made by the liver.Reflects longer-term nutritional and hepatic status, and drags total calcium down with it when low. |
| Bilirubin, total | 0.3–1.0mg/dL | Haem breakdown product processed by the liver.Visible jaundice appears well above the upper limit, so a raised bilirubin precedes anything you can see. |
| Aspartate aminotransferase (AST) | 10–40U/L | An enzyme released from injured cells.Found in heart and skeletal muscle as well as liver, so a rise is not automatically hepatic. |
| Alkaline phosphatase (ALP) | 30–120U/L | An enzyme concentrated in bile ducts and bone.Raised in biliary obstruction and in bone disease — the pairing with bilirubin usually tells you which. |
Arterial blood gases
| Test | Common reference range | What it measures and why it matters |
|---|---|---|
| pH, arterial | 7.38–7.44 | Blood acidity, on room air.The first thing to read on a gas: it tells you whether the disturbance has been compensated, and in which direction.Sources differ: This is the value most worth understanding. ABIM's exam sheet gives 7.38–7.44; nursing teaching almost universally uses 7.35–7.45. Neither is wrong — they are different reference populations and methods — but a student taught 7.35 as a hard boundary will mis-read an item built on the narrower range. |
| PaCO₂, arterial | 38–42mm Hg | Dissolved carbon dioxide — the respiratory half of acid–base balance.Moves in the opposite direction to pH in a respiratory problem, and the same direction in compensation.Sources differ: ABIM gives 38–42 mm Hg; nursing convention teaches 35–45. |
| PaO₂, arterial | 75–100mm Hg | Dissolved oxygen in arterial blood, breathing room air.The measured partner to pulse oximetry, which estimates saturation rather than measuring dissolved oxygen. |
| Bicarbonate (HCO₃⁻), arterial | 23–26mEq/L | The metabolic half of acid–base balance.Moves with pH in a metabolic problem and against it when the kidney is compensating for a respiratory one.Sources differ: ABIM lists arterial bicarbonate as 23–26 mEq/L and serum bicarbonate separately — legitimately, because they are different specimens and methods. A single 'bicarbonate' row that ignores the specimen is hiding a real distinction. |
| Oxygen saturation, arterial | ≥95% | The percentage of hemoglobin carrying oxygen.Target saturations are condition-specific — a patient with chronic CO₂ retention is managed to a lower target on purpose. |
Coagulation
| Test | Common reference range | What it measures and why it matters |
|---|---|---|
| Prothrombin time (PT) | 11–13seconds | Speed of clotting through the extrinsic pathway.The raw seconds are laboratory-specific, which is exactly why the INR exists. |
| Activated partial thromboplastin time (aPTT) | 25–35seconds | Speed of clotting through the intrinsic pathway.Monitors unfractionated heparin; the therapeutic target is a multiple of the laboratory's own control, not a fixed number. |
Cardiac markers
| Test | Common reference range | What it measures and why it matters |
|---|---|---|
| Troponin I, cardiac | ≤0.04ng/mL | A protein released when cardiac muscle is injured.Highly specific to cardiac muscle injury, and the trend across serial draws carries more information than any single result.Sources differ: Troponin has no universal normal value and CARE will not publish one as if it did. There is no primary reference material for cardiac troponin I, so assays cannot be standardised against each other: three high-sensitivity assays measured on one reference population produced 99th-percentile limits of roughly 10, 17 and 17 ng/L, and another comparison gave 21, 31 and 28. Your laboratory's own limit is the only one that applies, and modern limits are sex-specific. |
Glucose
| Test | Common reference range | What it measures and why it matters |
|---|---|---|
| Hemoglobin A1c | 4.0–5.6% | The proportion of hemoglobin that is glycated — average glycaemia over roughly three months.The least laboratory-variable value on this page, because NGSP certifies methods as traceable to a single standard. That is why a fixed diagnostic cut-point is defensible for A1c and not for troponin. |
Endocrine
| Test | Common reference range | What it measures and why it matters |
|---|---|---|
| Thyroid-stimulating hormone (TSH) | 0.5–4.0μU/mL | The pituitary signal driving thyroid hormone production.Moves opposite to thyroid hormone — a high TSH means an underactive thyroid, which is the reverse of most students' first instinct. |
Guideline thresholds — a different kind of number
These are not reference intervals and are kept apart on purpose. They are decision points chosen by guideline committees from outcome risk. They do not vary between laboratories — but they do change when the committee changes them, so they carry the body and the year.
Hemoglobin A1c — diagnostic cut-points
- Normal
- below 5.7%
- Prediabetes
- 5.7% to 6.4%
- Diabetes
- 6.5% or above
These are diagnostic decision points chosen by a guideline committee, not a laboratory reference interval. They do not vary by laboratory — but they do change when the committee changes them. Set by American Diabetes Association, restated by NIDDK — NIDDK, Diabetes Tests & Diagnosis, read 2026-09-03.
Fasting plasma glucose — diagnostic cut-points
- Normal
- 99 mg/dL or below
- Prediabetes
- 100 to 125 mg/dL
- Diabetes
- 126 mg/dL or above
A diagnostic threshold, not a reference range. The fasting requirement is part of the definition — a random glucose is interpreted against different criteria. Set by American Diabetes Association, restated by NIDDK — NIDDK, Diabetes Tests & Diagnosis, read 2026-09-03.
Test yourself
Reading a reference table is not the same as recognising an abnormal result under time pressure. Our free quiz draws from the real question bank — including items where interpreting a value is the whole question.
This page is educational exam-preparation material. It is not clinical guidance and must not be used to interpret a real patient’s results — interpret those against the reference range printed on that patient’s own report, alongside their clinical picture.