Reference
Normal values
Common adult reference intervals with the context that makes each test worth ordering. Real laboratories publish their own intervals; always interpret against the reporting lab's ranges.
Electrolytes
| Test | Reference interval | Context |
|---|---|---|
| Sodium (Na) | 135–145 mmol/L | Water balance relative to solute; disorders are usually water problems, not salt problems. |
| Potassium (K) | 3.5–5 mmol/L | The membrane potential electrolyte; extremes threaten cardiac conduction. |
| Chloride (Cl) | 98–106 mmol/L | Follows sodium and acid-base; needed for the anion gap. |
| Bicarbonate (HCO3) | 22–28 mmol/L | The metabolic side of acid-base balance. |
| Calcium (corrected) (Ca) | 2.12–2.62 mmol/L | Interpret with albumin; symptoms track the ionized fraction. |
| Magnesium (Mg) | 0.7–1 mmol/L | The forgotten electrolyte; low magnesium keeps potassium low. |
| Phosphate (PO4) | 0.8–1.45 mmol/L | Cell energy currency; watch it in refeeding and DKA treatment. |
Endocrine
| Test | Reference interval | Context |
|---|---|---|
| Glucose (random) (Glu) | 4–7.8 mmol/L | Interpret against fasting state; extremes are emergencies. |
| TSH (TSH) | 0.4–4 mIU/L | The screening test of thyroid function; interpret with free T4 when abnormal. |
| Free T4 (fT4) | 10–20 pmol/L | Confirms and grades what the TSH suggests. |
| HbA1c (A1c) | 4–5.9 % | Three months of average glycemia in one number. |
Renal
| Test | Reference interval | Context |
|---|---|---|
| Creatinine (Cr) | 60–110 µmol/L | Filtration marker; the trend matters more than any single value. |
| Urea (Urea) | 2.5–8 mmol/L | Rises with hypoperfusion, GI bleed, and catabolism, out of proportion in prerenal states. |
| Urate (Urate) | 150–420 µmol/L | Purines' end product; climbs when cells lyse en masse and precipitates in tubules and joints. |
Hematology
| Test | Reference interval | Context |
|---|---|---|
| Hemoglobin (Hb) | 120–160 g/L | Oxygen-carrying capacity; interpret with the MCV and the reticulocytes. |
| White cell count (WBC) | 4–11 ×10⁹/L | Inflammation and infection marker; the differential tells you which arm. |
| Neutrophils (Neut) | 2–7.5 ×10⁹/L | The count that defines neutropenia; below 0.5 with a fever is an emergency on its own. |
| Platelets (Plt) | 150–400 ×10⁹/L | Bleeding risk climbs as counts fall; always confirm a surprise low count. |
| Mean corpuscular volume (MCV) | 80–100 fL | The first branch point of every anemia workup. |
| Reticulocytes (absolute) (Retic) | 20–100 ×10⁹/L | Is the marrow responding? High means loss or destruction; low means underproduction. |
| Lactate dehydrogenase (LDH) | 125–220 U/L | Cell turnover and lysis; part of the hemolysis screen. |
| Haptoglobin (Hapto) | 0.3–2 g/L | Consumed by free hemoglobin; low in hemolysis. |
Iron studies
| Test | Reference interval | Context |
|---|---|---|
| Ferritin (Ferr) | 30–300 µg/L | Iron stores, but also an acute-phase reactant; low is specific, normal excludes little when inflamed. |
| Serum iron (Fe) | 10–30 µmol/L | Fluctuates by the hour; never interpret alone. |
| Total iron binding capacity (TIBC) | 45–70 µmol/L | Rises in iron deficiency, falls in inflammation. |
| Transferrin saturation (TSat) | 20–50 % | Iron over TIBC; low in deficiency, high in overload. |
Liver
| Test | Reference interval | Context |
|---|---|---|
| Alanine aminotransferase (ALT) | 7–40 U/L | The more liver-specific transaminase; hepatocellular injury marker. |
| Aspartate aminotransferase (AST) | 10–40 U/L | Also in muscle and red cells; an AST-dominant pattern has its own differential. |
| Alkaline phosphatase (ALP) | 40–120 U/L | Cholestasis and bone; confirm hepatic origin with GGT. |
| Gamma-glutamyl transferase (GGT) | 8–60 U/L | Confirms a hepatic source for a raised ALP. |
| Total bilirubin (Bili) | 3–21 µmol/L | Fractionate when raised: unconjugated points to hemolysis or Gilbert, conjugated to the liver or the ducts. |
| Lipase (Lip) | 13–60 U/L | The pancreatic enzyme; three times the upper limit supports pancreatitis, but the height does not grade severity. |
| Albumin (Alb) | 35–50 g/L | Synthetic function and nutrition, and the correction factor for calcium and the anion gap. |
Coagulation
| Test | Reference interval | Context |
|---|---|---|
| INR (INR) | 0.9–1.1 | Extrinsic pathway; the liver's fastest synthetic read-out. |
| aPTT (aPTT) | 25–35 s | Intrinsic pathway; heparin effect and factor deficiencies. |
| Fibrinogen (Fib) | 1.5–4 g/L | An acute-phase clotting substrate; the number that falls when coagulation is being consumed. |
Cardiac
| Test | Reference interval | Context |
|---|---|---|
| High-sensitivity troponin (Trop) | 0–14 ng/L | Myocardial injury, not infarction by itself; the delta and the clinical picture make the diagnosis. |
| NT-proBNP (NT-proBNP) | 0–125 ng/L | Ventricular wall stress; strong negative predictive value for heart failure when low. |
| Creatine kinase (CK) | 30–200 U/L | Muscle injury at any scale; in rhabdomyolysis it counts the damage and predicts the kidney's risk. |
Inflammation
| Test | Reference interval | Context |
|---|---|---|
| C-reactive protein (CRP) | 0–5 mg/L | Fast-moving acute-phase reactant; trends track treatment response. |
Nutritional
| Test | Reference interval | Context |
|---|---|---|
| Vitamin B12 (B12) | 150–600 pmol/L | Macrocytosis, neuropathy, and cytopenias when deficient. |
Gases & perfusion
| Test | Reference interval | Context |
|---|---|---|
| Lactate (Lact) | 0.5–2.2 mmol/L | Tissue perfusion read-out; clearance is the resuscitation end point. |