Common Lab Values to Know

By VeriScorePrep Team · 6 min

Memorizing common reference ranges accelerates interpretation and lets you identify urgent abnormalities.

Sodium: 135–145 mEq/L

Low: SIADH, heart failure, diuretics, GI loss. High: dehydration, diabetes insipidus, high sodium intake.

Potassium: 3.5–5.0 mEq/L

Both extremes threaten the heart. Hypokalemia: diuretics. Hyperkalemia: renal failure, ACE inhibitors, potassium-sparing diuretics.

BUN: 7–20 mg/dL; Creatinine: 0.6–1.2 mg/dL

Kidney markers. BUN/Cr ratio >20:1 suggests pre-renal causes (dehydration, heart failure).

Glucose: 70–100 mg/dL (fasting)

Below 70 with symptoms: hypoglycemia — treat with fast carbohydrates. Above 200 with acidosis: DKA pattern.

White blood cells: 4,500–11,000/mm³

Below: infection risk, marrow suppression. Above: infection, inflammation, leukemia. Differentiate by differential — bands suggest bacterial infection.

Hemoglobin: 13.5–17.5 g/dL (men), 12–15.5 g/dL (women)

Low: anemia, bleeding. High: dehydration, polycythemia, high altitude.

Platelets: 150,000–400,000/mm³

Below 150,000: thrombocytopenia — watch for bleeding.

PT/INR: INR 1.0; therapeutic 2–3 (varies)

Monitors warfarin. Critical to keep stable for patients on anticoagulation.

aPTT: 30–40 sec

Monitors heparin.

Magnesium: 1.5–2.5 mEq/L

Low: arrhythmias, hypokalemia that resists correction.

Calcium: 8.5–10.5 mg/dL

Low: tetany, post-thyroidectomy. High: hyperparathyroidism, malignancy.

Reference ranges vary slightly by lab; always confirm against your facility's values.