LAB TESTS EXPLAINED
1. Kidney Function Tests (KFT)
These tests show how well the kidneys filter waste, balance electrolytes, and regulate blood composition.
Urea:
Formed when proteins are broken down. It is excreted by the kidneys.
- High: Kidney failure, dehydration, high-protein diet, gastrointestinal bleed.
- Low: Liver disease (reduced urea formation), low protein intake, over-hydration.
Sequence: If kidneys fail, urea formed in the liver cannot be excreted → accumulates in blood → high value.
Creatinine:
Produced by muscle metabolism and excreted by kidneys.
- High: Reduced kidney filtration (renal failure), obstruction, dehydration.
- Low: Low muscle mass, liver disease, pregnancy.
Sequence: Impaired glomerular filtration → creatinine retained in blood → high value.
Uric acid:
End product of purine (DNA) breakdown.
- High: Gout, kidney disease, high purine diet, chemotherapy.
- Low: Low protein diet, liver disease.
Electrolytes (Sodium, Potassium, Chloride):
They help maintain fluid balance, nerve and muscle function.
- High sodium: Dehydration, excess salt intake, Cushing’s.
- Low sodium: Vomiting, diarrhea, renal loss, SIADH.
- High potassium: Kidney failure, acidosis, cell breakdown.
- Low potassium: Diuretics, vomiting, diarrhea.
- High chloride: Dehydration, acidosis.
- Low chloride: Vomiting, metabolic alkalosis.
Calcium and Phosphorus:
Control bone metabolism and muscle contraction.
- High calcium: Hyperparathyroidism, bone destruction, cancer.
- Low calcium: Vitamin D deficiency, renal disease.
- High phosphorus: Kidney failure.
- Low phosphorus: Vitamin D deficiency, malnutrition.
When calcium ↓ and phosphorus ↑ — indicates chronic kidney disease.
2. Liver Function Tests (LFT)
These evaluate liver cell integrity, bile flow, and protein synthesis.
Bilirubin (Total, Direct, Indirect):
Formed from RBC breakdown.
- High total/direct: Liver disease or bile obstruction.
- High indirect: Excess RBC breakdown (hemolysis).
If both direct and indirect high → hepatic jaundice; if direct high alone → obstructive jaundice.
Total Protein, Albumin, Globulin, A/G Ratio:
Reflect liver synthetic capacity.
- Low albumin: Liver disease, malnutrition, kidney loss (nephrotic).
- High globulin: Chronic inflammation, autoimmune disease.
- Low A/G ratio: Chronic liver or renal disease.
SGOT (AST) and SGPT (ALT):
Enzymes released from liver cells.
- High: Hepatitis, fatty liver, alcohol toxicity.
- ALT more specific for liver; AST also rises in heart and muscle damage.
Sequence: Hepatocyte damage → enzyme leakage → rise in blood.
Alkaline phosphatase (ALP):
From bile duct and bone.
- High: Bile obstruction, bone disease, liver metastasis.
GGT:
Specific to liver and bile duct.
- High: Alcohol abuse, cholestasis, certain drugs.
Combination: ALP ↑ + GGT ↑ = biliary obstruction; ALP ↑ alone = bone cause.
3. Thyroid Function Tests (T3, T4, TSH)
Show thyroid hormone production and pituitary control.
- High T3/T4, low TSH: Hyperthyroidism (thyroid overactive).
- Low T3/T4, high TSH: Primary hypothyroidism.
- All low: Secondary hypothyroidism (pituitary failure).
Sequence: Pituitary releases TSH → thyroid produces T3, T4 → negative feedback maintains balance.*
4. Diabetic Profile
Fasting glucose:
Shows present glucose control.
- High: Diabetes, stress, hyperthyroidism.
- Low: Insulin overdose, liver disease, starvation.
HbA1c:
Reflects average blood sugar of past 3 months.
- <5.7%: Normal
- 5.7–6.4%: Prediabetes
- ≥6.5%: Diabetes
Combination: Normal fasting glucose but high HbA1c = past poor control; both high = current and chronic hyperglycemia.*
5. Lipid Profile
Indicates fat metabolism and cardiovascular risk.
Total Cholesterol:
Sum of all cholesterol fractions.
- High: Atherosclerosis risk, hypothyroidism, high-fat diet.
Triglycerides:
Energy source from fat.
- High: Diabetes, obesity, alcohol intake, high-carb diet.
- Low: Malnutrition, hyperthyroidism.
HDL (good cholesterol):
Removes cholesterol from tissues.
- High: Protective.
- Low: Risk for heart disease.
LDL (bad cholesterol):
Carries cholesterol to tissues and arteries.
- High: Major risk for atherosclerosis.
- Low: Liver or malabsorption issues.
VLDL:
Transports triglycerides.
- High: Seen in obesity and metabolic syndrome.
Clinical combinations:
- High LDL + High Triglycerides + Low HDL = Metabolic syndrome or diabetes-related dyslipidemia.
- High cholesterol + High ALP + High GGT = liver origin of lipid disturbance.
6. Complete Blood Count (CBC)
Evaluates red cells, white cells, and platelets.
Haemoglobin, RBC, PCV:
Show oxygen-carrying capacity.
- Low: Anaemia (blood loss, iron/B12 deficiency).
- High: Polycythemia, dehydration.
MCV, MCH, MCHC:
Indices to classify anaemia:
- Low MCV: Microcytic (iron deficiency).
- High MCV: Macrocytic (B12/folate deficiency).
WBC Count and Differential:
Defend against infection.
- High WBC: Infection, inflammation.
- Low: Viral infection, bone marrow suppression.
- Neutrophil dominance: Bacterial infection.
- Lymphocyte dominance: Viral infection.
Platelet count:
- Low: Bleeding tendency.
- High: Chronic inflammation, post-surgery.
7. ESR (Erythrocyte Sedimentation Rate)
Non-specific marker of inflammation.
- High: Chronic infections, autoimmune diseases, anemia.
- Low: Polycythemia, heart failure.
8. Iron Studies
Serum Iron: Circulating iron.
TIBC: Ability of transferrin to carry iron.
Transferrin Saturation: Percent of transferrin bound with iron.
UIBC: Portion of transferrin still free to bind iron.
- Low iron + High TIBC + Low saturation = Iron deficiency.
- High iron + Low TIBC = Hemolysis, liver disease.
9. Vitamin Tests
Vitamin B12: Needed for RBC formation and nerve function.
- Low: Pernicious anaemia, malabsorption, chronic gastritis, metformin use.
- High: Liver disease, supplementation.
Vitamin D (25-OH): Regulates calcium and bone health.
- Low: Rickets, osteomalacia, weak bones.
- High: Over-supplementation or excessive sun exposure.
10. Urine Routine
Assesses kidney and metabolic health.
Normal results indicate normal filtration, no infection, and balanced hydration.
- Protein present: Glomerular leak.
- Sugar present: Diabetes.
- Blood present: Infection, stones.
- High specific gravity: Dehydration.
- Low specific gravity: Renal tubular dysfunction.
Common Combination Patterns and Their Meaning
| Pattern | Likely Condition |
|---|---|
| Urea ↑ + Creatinine ↑ | Renal failure or dehydration |
| SGPT ↑ + SGOT ↑ + ALP normal | Hepatocellular damage (Hepatitis) |
| ALP ↑ + GGT ↑ | Obstructive jaundice or biliary disease |
T3/T4 low + TSH high |
Hypothyroidism |
Glucose ↑ + HbA1c ↑ |
Poor diabetic control |
Iron ↓ + TIBC ↑ |
Iron deficiency anaemia |
Cholesterol ↑ + LDL ↑ + HDL ↓ |
High cardiac risk |
Vitamin D ↓ + Calcium ↓ + Phosphorus ↑ |
Chronic kidney disease |
