📌 Biochemistry Tests – Interpretation for Clinical Diagnosis
Biochemistry tests analyze enzymes, proteins, electrolytes, and metabolic markers to diagnose and monitor diseases. These tests are crucial in internal medicine, pediatrics, nephrology, cardiology, and endocrinology.
🔹 Key Biochemistry Tests & Clinical Interpretation
1️⃣ Liver Function Tests (LFTs)
| Test | Normal Range | Clinical Interpretation |
|---|---|---|
| Total Bilirubin | 0.2 – 1.2 mg/dL | ↑ in liver disease, hemolysis |
| Direct Bilirubin | 0.1 – 0.4 mg/dL | ↑ in obstructive jaundice |
| ALT (Alanine Aminotransferase) | 7 – 55 U/L | ↑ in liver damage (viral hepatitis, fatty liver) |
| AST (Aspartate Aminotransferase) | 10 – 40 U/L | ↑ in liver & muscle damage (alcoholic hepatitis, MI) |
| ALP (Alkaline Phosphatase) | 44 – 147 U/L | ↑ in bile obstruction, bone disease |
| GGT (Gamma-Glutamyl Transferase) | 9 – 48 U/L | ↑ in alcohol-related liver disease |
| Albumin | 3.5 – 5.5 g/dL | ↓ in chronic liver disease, nephrotic syndrome |
| Prothrombin Time (PT/INR) | INR < 1.2 | ↑ in liver failure, vitamin K deficiency |
📌 Liver Injury Patterns
- Hepatocellular injury (↑ ALT & AST) → Hepatitis, NAFLD
- Cholestasis (↑ ALP & GGT) → Biliary obstruction
- Synthetic failure (↓ Albumin, ↑ PT/INR) → Chronic liver disease
2️⃣ Kidney Function Tests (KFTs)
| Test | Normal Range | Clinical Interpretation |
|---|---|---|
| Creatinine | 0.6 – 1.2 mg/dL | ↑ in kidney dysfunction |
| Blood Urea Nitrogen (BUN) | 6 – 20 mg/dL | ↑ in dehydration, renal failure |
| BUN/Creatinine Ratio | 10:1 – 20:1 | ↑ in prerenal AKI (dehydration), ↓ in intrinsic renal disease |
| eGFR (Estimated Glomerular Filtration Rate) | >90 mL/min | ↓ in CKD stages (1-5) |
| Uric Acid | 3.5 – 7.2 mg/dL | ↑ in gout, kidney stones |
| Urine Protein (Dipstick/24hr) | <150 mg/day | ↑ in nephrotic syndrome (>3.5g/day) |
📌 Acute vs Chronic Kidney Disease
- AKI (Acute Kidney Injury): Rapid ↑ creatinine, BUN, electrolyte imbalance
- CKD (Chronic Kidney Disease): Persistent eGFR decline, anemia, hyperkalemia
3️⃣ Electrolyte Panel
| Test | Normal Range | Clinical Interpretation |
|---|---|---|
| Sodium (Na⁺) | 135 – 145 mmol/L | ↓ in SIADH, CHF; ↑ in dehydration |
| Potassium (K⁺) | 3.5 – 5.0 mmol/L | ↑ in renal failure, ACE inhibitors; ↓ in diarrhea, diuretics |
| Chloride (Cl⁻) | 96 – 106 mmol/L | ↑ in dehydration, metabolic acidosis |
| Bicarbonate (HCO₃⁻) | 22 – 28 mmol/L | ↓ in metabolic acidosis |
| Calcium (Ca²⁺) | 8.5 – 10.5 mg/dL | ↓ in hypoparathyroidism, CKD; ↑ in hyperparathyroidism |
| Magnesium (Mg²⁺) | 1.5 – 2.5 mg/dL | ↓ in alcoholism, ↑ in renal failure |
📌 Common Electrolyte Disorders:
- Hyponatremia (↓ Na⁺): SIADH, heart failure, cirrhosis
- Hyperkalemia (↑ K⁺): CKD, ACE inhibitors, Addison’s disease
4️⃣ Diabetes & Lipid Profile
| Test | Normal Range | Clinical Interpretation |
|---|---|---|
| Fasting Blood Glucose (FBG) | 70 – 100 mg/dL | ≥126 mg/dL = Diabetes |
| Postprandial Glucose (PPG) | <140 mg/dL | ≥200 mg/dL = Diabetes |
| HbA1c (Glycated Hemoglobin) | <5.7% | ≥6.5% = Diabetes |
| Total Cholesterol | <200 mg/dL | ↑ in hyperlipidemia, CVD |
| LDL (Bad Cholesterol) | <100 mg/dL | ↑ in atherosclerosis |
| HDL (Good Cholesterol) | >40 mg/dL (M), >50 mg/dL (F) | ↓ in metabolic syndrome |
| Triglycerides | <150 mg/dL | ↑ in pancreatitis, diabetes |
📌 Diabetes Diagnosis Criteria:
- Fasting Glucose ≥126 mg/dL OR HbA1c ≥6.5%
- 2-hour OGTT Glucose ≥200 mg/dL
📌 Lipid Disorders:
- High LDL + Low HDL = Atherosclerosis Risk
- Triglycerides >500 mg/dL → Risk of pancreatitis
5️⃣ Cardiac Biomarkers
| Test | Normal Range | Clinical Interpretation |
|---|---|---|
| Troponin I/T | <0.01 ng/mL | ↑ in acute MI (peaks 12-24h) |
| CK-MB (Creatine Kinase-MB) | <5 ng/mL | ↑ in myocardial injury |
| BNP (Brain Natriuretic Peptide) | <100 pg/mL | ↑ in heart failure |
| D-Dimer | <0.5 µg/mL | ↑ in DVT, PE, DIC |
📌 Acute Myocardial Infarction (MI) Diagnosis:
- Troponin I >0.1 ng/mL + ST Elevation → STEMI
- Normal ECG + ↑ Troponins → NSTEMI
📍 Sample Clinical Cases for Biochemistry Tests
🔹 Case 1: Diabetic Ketoacidosis (DKA)
- Patient: 20-year-old male, Type 1 DM, confusion, dehydration
- Findings:
- Glucose: 500 mg/dL
- pH: 7.2 (Acidosis)
- HCO₃⁻: 12 mmol/L (↓ Metabolic Acidosis)
- Ketones: Positive
- Diagnosis: DKA
- Treatment: IV Insulin, Fluids, Potassium correction
🔹 Case 2: Myocardial Infarction (MI)
- Patient: 55-year-old male, chest pain, sweating
- Findings:
- Troponin I: 0.5 ng/mL (↑)
- CK-MB: 10 ng/mL (↑)
- ECG: ST Elevation in leads II, III, aVF
- Diagnosis: STEMI
- Treatment: Immediate PCI, Aspirin, Heparin