LAB TESTS EXPLAINED

LAB TESTS EXPLAINED

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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.

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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.

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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.*

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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.*

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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.

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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.

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7. ESR (Erythrocyte Sedimentation Rate)

Non-specific marker of inflammation.

• High: Chronic infections, autoimmune diseases, anemia.
• Low: Polycythemia, heart failure.

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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.

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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.

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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.

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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

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