Organ function tests are essential diagnostic tools used to assess how well major organs like the kidney and liver are working. These tests help detect diseases early, guide treatment and monitor the progress of therapy. This chapter explains the functions of the kidney and liver, routine laboratory tests and their clinical significance in simple language.
ACTUAL NOTES:
Organ Function Tests: Kidney Tests, Liver Tests and Lipid Profile
Organ function tests are essential diagnostic tools used to assess how well major organs like the kidney and liver are working. These tests help detect diseases early, guide treatment and monitor the progress of therapy. This chapter explains the functions of the kidney and liver, routine laboratory tests and their clinical significance in simple language.
Kidney Function and Routine Kidney Function Tests (KFT)
Functions of the Kidney
The kidneys are vital organs responsible for filtering blood and maintaining internal balance. Their major functions include:
- Excretion of waste products: Removes urea, creatinine and uric acid.
- Regulation of water and electrolyte balance: Controls sodium, potassium and water levels.
- Acid–base balance: Maintains body pH by excreting hydrogen ions.
- Hormone production: Produces erythropoietin (RBC formation), renin (blood pressure control) and activates vitamin D.
- Regulation of blood pressure: Through renin–angiotensin system.
Routinely Performed Kidney Function Tests
1. Serum Urea
- Normal range: 15–40 mg/dL
- High levels indicate: Kidney failure, dehydration, high protein breakdown.
2. Serum Creatinine
- Normal range: 0.6–1.3 mg/dL
- Most reliable indicator of kidney function.
- High creatinine = reduced kidney filtration (renal impairment).
3. Blood Urea Nitrogen (BUN)
- Normal range: 7–20 mg/dL
- High BUN suggests kidney dysfunction or dehydration.
4. Creatinine Clearance Test
Measures how well the kidneys filter creatinine. Helps estimate glomerular filtration rate (GFR).
5. Estimated GFR (eGFR)
- Normal: > 90 mL/min
- Reduced GFR indicates stages of chronic kidney disease (CKD).
6. Urine Routine and Microscopy
- Checks protein, glucose, ketones, RBCs, WBCs.
- Protein in urine (proteinuria) suggests kidney damage.
Clinical Significance of Kidney Function Tests
- Diagnose acute and chronic kidney disease.
- Detect dehydration, urinary tract obstruction and kidney infections.
- Monitor patients on nephrotoxic drugs (aminoglycosides, NSAIDs).
- Evaluate hypertension and diabetes complications.
Liver Function and Routine Liver Function Tests (LFT)
Functions of the Liver
The liver is the largest metabolic organ in the body with essential functions:
- Metabolism: Carbohydrates, proteins and fats.
- Detoxification: Converts toxins and drugs into harmless forms.
- Bile production: Needed for fat digestion.
- Storage: Stores vitamins A, D, B12, iron and glycogen.
- Protein synthesis: Produces albumin and clotting factors.
Routinely Performed Liver Function Tests
1. Serum Bilirubin (Total, Direct, Indirect)
- Total normal: 0.3–1.2 mg/dL
- High bilirubin indicates jaundice, liver dysfunction or bile obstruction.
2. Serum Enzymes
- ALT (Alanine transaminase): Elevated in liver cell injury.
- AST (Aspartate transaminase): Increased in liver disease and muscle injury.
- ALP (Alkaline phosphatase): High in bile duct obstruction, bone disorders.
- GGT (Gamma-glutamyl transferase): High in alcohol-related liver damage.
3. Serum Albumin
- Normal: 3.5–5.5 g/dL
- Low albumin suggests chronic liver disease or malnutrition.
4. Prothrombin Time (PT/INR)
- Liver makes clotting factors; prolonged PT indicates liver failure.
Clinical Significance of Liver Function Tests
- Diagnose hepatitis, liver cirrhosis and jaundice.
- Detect bile duct obstruction and alcohol-induced liver injury.
- Monitor drug toxicity (e.g., paracetamol overdose).
- Assess progression of chronic liver disease.
Lipid Profile Tests
Lipid profile measures different types of fats in the blood to assess risk of heart disease.
Components of Lipid Profile
1. Total Cholesterol
- Normal: Less than 200 mg/dL
2. LDL Cholesterol (“Bad Cholesterol”)
- Optimal: Less than 100 mg/dL
- High LDL increases risk of atherosclerosis and heart attack.
3. HDL Cholesterol (“Good Cholesterol”)
- Normal: 40–60 mg/dL
- High HDL protects against heart disease.
4. Triglycerides
- Normal: Less than 150 mg/dL
- High levels associated with pancreatitis and metabolic syndrome.
5. VLDL (Very Low-Density Lipoprotein)
Transports triglycerides in the blood. High levels correlate with obesity and diabetes.
Clinical Significance of Lipid Profile
- Assesses risk of heart disease, stroke and atherosclerosis.
- Monitors patients on lipid-lowering medications (statins).
- Helps diagnose metabolic syndrome and diabetes-related complications.
- Guides dietary and lifestyle interventions.
