Understanding Reference Ranges: A reference range is a set of values that includes 95% of the normal, healthy population. A result outside this range doesn't automatically mean disease, and a result within it doesn't guarantee health. All test results must be interpreted in the context of the individual patient's clinical presentation.
Full Blood Count (FBC)
Red Blood Cells (RBCs)
| Test | Normal Range | Clinical Significance |
|---|---|---|
| Haemoglobin (Hb) | Men: 130-180 g/L Women: 115-165 g/L | Measures oxygen-carrying capacity. Decreased in anemia. Increased in polycythemia or dehydration. |
| Haematocrit (Hct) | Men: 40-50% Women: 36-47% | Percentage of blood volume occupied by RBCs. Parallels Hb levels. |
| Mean Corpuscular Volume (MCV) | 80-98 fL | Average size of one RBC. Used to classify anemia as microcytic (<80), normocytic (80-98), or macrocytic (>98). |
| Mean Corpuscular Haemoglobin (MCH) | 27-32 pg | Average weight of Hb in each RBC. |
| Mean Corpuscular Haemoglobin Concentration (MCHC) | 300-350 g/L | Concentration of Hb in RBCs. Used to classify anemia as hypochromic (low) or normochromic (normal). |
White Blood Cells (WBCs)
| Test | Normal Range | Clinical Significance |
|---|---|---|
| Total WCC | 4-10 x 10⁹/L | Measures total number of leukocytes. High (leukocytosis) suggests infection/inflammation. Low (leukopenia) suggests bone marrow suppression. |
| Neutrophils | 2.5-7.5 x 10⁹/L (40-75%) | Increased (neutrophilia) in bacterial infections and tissue damage. |
| Lymphocytes | 1.0-3.5 x 10⁹/L (20-45%) | Increased (lymphocytosis) in viral infections. |
| Monocytes | 0.2-0.8 x 10⁹/L (2-10%) | Increased in chronic bacterial infections (e.g., TB) and autoimmune diseases. |
| Eosinophils | 0.04-0.4 x 10⁹/L (1-6%) | Increased (eosinophilia) in allergic reactions and parasitic infections. |
| Basophils | 0.01-0.1 x 10⁹/L (0-1%) | Increased in some allergic reactions. |
Platelets
| Test | Normal Range | Clinical Significance |
|---|---|---|
| Platelet Count | 150-400 x 10⁹/L | Measures platelets (thrombocytes). Low (thrombocytopenia) increases bleeding risk. High (thrombocytosis) can increase thrombosis risk. |
Inflammatory Markers
| Test | Normal Range | Clinical Significance |
|---|---|---|
| Erythrocyte Sedimentation Rate (ESR) | < 16 mm/hour | A non-specific marker of inflammation. Elevated in infections, autoimmune diseases, and malignancy. |
| C-reactive Protein (CRP) | < 5 mg/L | A more sensitive and specific marker of acute inflammation. Rises quickly in response to infection and tissue injury. |
Iron Studies
| Test | Normal Range | Clinical Significance |
|---|---|---|
| Serum Iron | 10-30 µmol/L | Measures iron bound to transferrin. Highly variable and of little value alone. |
| Serum Ferritin | 15-300 µg/L | Measures the body's iron stores. Best indicator of iron deficiency (low levels). |
| Transferrin / TIBC | 1.7-3.0 g/L / 45-80 µmol/L | Transferrin is the main iron transport protein. Both increase in iron deficiency. |
| Transferrin Saturation | 15-45% | Percentage of transferrin saturated with iron. Decreased in iron deficiency, increased in iron overload. |
Glucose Tests
| Test | Normal / Desirable Range | Clinical Significance |
|---|---|---|
| Fasting Blood Glucose | 3.0-5.5 mmol/L | > 7.0 mmol/L is diagnostic for diabetes mellitus. |
| Random Blood Glucose | 3.3-7.7 mmol/L | Used for opportunistic screening. |
| Oral Glucose Tolerance Test (OGTT) | 2-hour level < 7.7 mmol/L | Used to diagnose diabetes when fasting glucose is borderline. A 2-hour level > 11.1 mmol/L is diagnostic. |
| Glycosylated Haemoglobin (HbA1c) | 3.5-6.0% (15-42 mmol/mol) | Reflects average blood glucose over ~3 months. Used to monitor long-term control in diabetics (target < 7.0%). |
Lipid Profile
| Test | Desirable Level | Clinical Significance |
|---|---|---|
| Total Cholesterol (TC) | < 5.5 mmol/L (Ideal < 4.0) | Total amount of cholesterol. High levels are a risk factor for atherosclerosis. |
| LDL Cholesterol ("Bad") | < 3.0 mmol/L | Transports cholesterol to tissues. High levels are a major risk factor for atherosclerosis. |
| HDL Cholesterol ("Good") | > 1.0 mmol/L | Transports excess cholesterol back to the liver. High levels are protective. |
| Triglycerides (TG) | < 1.7 mmol/L | A type of fat in blood. High levels can be an independent risk factor for atherosclerosis. |
Cardiac Markers
| Marker | Normal Range | Clinical Significance |
|---|---|---|
| Cardiac Troponin (cTnT, cTnI) | Undetectable | The most sensitive and specific markers for myocardial necrosis (MI). Rise within 3-6 hours of an MI. |
| Creatine Kinase (CK-MB) | Essentially 0% of total CK | An isoenzyme found mainly in the heart. Rises in MI but is less specific than troponins. |
| Myoglobin | Variable | An early but non-specific marker of muscle injury (cardiac or skeletal). |
Liver Function Tests (LFTs)
| Test | Normal Range | Clinical Significance |
|---|---|---|
| Bilirubin | Variable (Total < 21 µmol/L) | Increased levels cause jaundice. Helps differentiate hepatocellular vs. cholestatic liver disease. |
| ALT (Alanine Aminotransferase) | < 40 IU/L | A specific marker for hepatocellular injury (e.g., viral hepatitis, toxic damage). |
| AST (Aspartate Aminotransferase) | < 40 IU/L | Less specific than ALT (also in heart/muscle), but a sensitive marker of liver cell damage. |
| ALP (Alkaline Phosphatase) | 30-120 IU/L | Elevated in cholestasis (bile duct obstruction) and certain bone diseases. |
| GGT (Gamma-Glutamyl Transferase) | < 50 IU/L | A sensitive marker of liver cell damage and cholestasis. Elevated by alcohol consumption. |
| Albumin | 35-50 g/L | A true test of liver *synthetic function*. Low levels suggest chronic liver disease or malnutrition. |
Tests of Haemostasis
| Test | Normal / Desirable Range | Clinical Significance |
|---|---|---|
| Prothrombin Time (PT) / INR | 11-13 sec / INR ~1.0 | Measures extrinsic/common pathways. Prolonged in liver disease, vit K deficiency. Used to monitor warfarin (target INR 2-3). |
| Activated Partial Thromboplastin Time (aPTT) | 25-35 sec | Measures intrinsic/common pathways. Prolonged in haemophilias. Used to monitor heparin. |
Kidney Function Tests
| Test | Normal Range | Clinical Significance |
|---|---|---|
| Urea | 3-8 mmol/L | Waste product of protein metabolism. Increases with impaired renal function or dehydration. |
| Creatinine | < 0.12 mmol/L | Waste product of muscle metabolism. A more reliable indicator of renal function than urea. |
| eGFR (Estimated GFR) | > 90 mL/min/1.73m² | Best overall indicator of kidney function. A value < 60 suggests chronic kidney disease. |
Electrolytes
| Test | Normal Range | Clinical Significance |
|---|---|---|
| Sodium (Na⁺) | 135-145 mmol/L | Major extracellular cation. Regulates osmotic pressure. Imbalances often reflect water balance issues. |
| Potassium (K⁺) | 3.5-5.3 mmol/L | Major intracellular cation. Crucial for nerve and muscle function. Imbalances can cause life-threatening cardiac arrhythmias. |
| Calcium (Ca²⁺) | 2.1-2.6 mmol/L (total) | Crucial for muscle contraction, nerve function, and blood clotting. Imbalances affect neuromuscular excitability. |
| Chloride (Cl⁻) | 96-106 mmol/L | Major extracellular anion. Levels generally follow sodium. |
Arterial Blood Gas (ABG) Analysis
| Parameter | Normal Range | Significance |
|---|---|---|
| pH | 7.35 - 7.45 | Measures acidity/alkalinity. < 7.35 = Acidosis, > 7.45 = Alkalosis. |
| PaCO₂ | 35 - 45 mmHg | The respiratory component. High in respiratory acidosis (hypoventilation), low in respiratory alkalosis (hyperventilation). |
| HCO₃⁻ | 22 - 26 mmol/L | The metabolic component. Low in metabolic acidosis, high in metabolic alkalosis. |
| PaO₂ | 80 - 100 mmHg | Measures adequacy of blood oxygenation. |
| Oxygen Saturation (SaO₂) | > 95% | Percentage of haemoglobin saturated with oxygen. |
Urine Tests (Urinalysis)
| Test | Normal Finding | Abnormal Finding Suggests |
|---|---|---|
| Specific Gravity (SG) | 1.010 - 1.025 | Hydration status. High SG = dehydration, Low SG = overhydration or diabetes insipidus. |
| pH | 4.6 - 8.0 | Can indicate systemic acid-base disorders or urinary tract infections. |
| Glucose | Negative | Diabetes mellitus. |
| Ketones | Negative | Diabetic ketoacidosis, starvation. |
| Protein | Negative/Trace | Kidney disease (e.g., glomerulonephritis, nephrotic syndrome). |
| Blood | Negative | UTI, kidney stones, glomerulonephritis, malignancy. |
| Leukocytes | Negative | Urinary tract infection (UTI). |
| Nitrites | Negative | Bacterial UTI (many common bacteria convert nitrates to nitrites). |