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Normal lab values

Adult reference ranges in the units used on the NCLEX and NP certification exams, with a one-line note on what each result usually means for the question in front of you.

Ranges differ between laboratories and assays. On an exam the range is printed beside the result, so read that one. For exam preparation only, not for patient care.

Electrolytes and chemistry

Test	Adult range	Exam note
Sodium (Na)	135–145 mEq/L	Low: confusion, seizures. Correct slowly to avoid osmotic demyelination.
Potassium (K)	3.5–5.0 mEq/L	Low or high both cause arrhythmias. Check the ECG and never give IV push.
Chloride (Cl)	98–106 mEq/L
Bicarbonate (HCO3)	22–28 mEq/L
Calcium, total	8.6–10.2 mg/dL	Low: tetany, Chvostek and Trousseau signs. High: bone pain, stones, constipation.
Magnesium (Mg)	1.5–2.5 mg/dL	On magnesium sulfate, check reflexes, respirations and urine output.
Phosphorus (Phos)	2.5–4.5 mg/dL	Rises when calcium falls, and in kidney disease.
Glucose, fasting	70–99 mg/dL	Under 70 is hypoglycemia: treat first, then investigate.
BUN	10–20 mg/dL
Creatinine	0.6–1.2 mg/dL	A better kidney marker than BUN, which also rises with dehydration and GI bleeding.
Anion gap	8–12 mEq/L	Na minus (Cl + HCO3). High gap points to lactic acidosis, DKA, uremia, toxins.
Lactate	0.5–2.0 mmol/L	Above 2 suggests poor perfusion; above 4 is a sepsis red flag.

Blood gases (arterial)

Test	Adult range	Exam note
pH	7.35–7.45
PaCO2	35–45 mmHg	Respiratory component. Up means acid, down means alkaline.
HCO3	22–26 mEq/L	Metabolic component. Up means alkaline, down means acid.
PaO2	80–100 mmHg
SaO2	95–100 %

Hematology

Test	Adult range	Exam note
Hemoglobin	Men 13.5–17.5 · Women 12.0–15.5 g/dL
Hematocrit	Men 41–50 · Women 36–44 %	Roughly three times the hemoglobin.
WBC	4,500–11,000 /mm³	Low count with fever (neutropenia) means protective isolation and urgent review.
Platelets	150,000–400,000 /mm³	Under 50,000 raises bleeding risk; under 20,000 risks spontaneous bleeding.

Coagulation

Test	Adult range	Exam note
PT	11–13.5 seconds
INR	0.8–1.1	Warfarin target is usually 2–3 (2.5–3.5 for some mechanical valves).
aPTT	25–35 seconds	Heparin target is usually 1.5–2.5 times the control value.

Cardiac

Test	Adult range	Exam note
Troponin I	Below the lab cutoff (often under 0.04) ng/mL	Assay-specific. A rising value points to myocardial injury.
BNP	Under 100 pg/mL	Elevated in heart failure.

Liver and thyroid

Test	Adult range	Exam note
AST	10–40 U/L
ALT	7–56 U/L
Total bilirubin	0.3–1.2 mg/dL
Albumin	3.5–5.0 g/dL
TSH	0.4–4.0 mIU/L	High TSH with low free T4 means primary hypothyroidism.
Free T4	0.8–1.8 ng/dL

Diabetes and lipids

Test	Adult range	Exam note
HbA1c	Normal under 5.7 · Prediabetes 5.7–6.4 · Diabetes 6.5 or higher %
Total cholesterol	Under 200 mg/dL
LDL	Under 100 (optimal) mg/dL
HDL	Above 40 men · above 50 women mg/dL
Triglycerides	Under 150 mg/dL

Drug levels (therapeutic)

Test	Adult range	Exam note
Lithium	0.6–1.2 mEq/L	Narrow window. Coarse tremor, vomiting, ataxia suggest toxicity. Sodium loss raises the level.
Digoxin	0.5–2.0 ng/mL	Low potassium makes toxicity more likely. Check apical pulse for a full minute.
Phenytoin	10–20 mcg/mL
Vancomycin trough	10–20 mcg/mL
Theophylline	10–20 mcg/mL

Urine and kidney

Test	Adult range	Exam note
Urine specific gravity	1.005–1.030	High suggests dehydration; low suggests overhydration or diabetes insipidus.
eGFR	Above 90 mL/min/1.73 m²	Under 60 for three months or more defines chronic kidney disease.

Know the number, then use it

Exam questions rarely ask for a range. They ask what you do next. Practice with free daily questions.

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