Introduction
- Triglycerides are the major form of stored fat in the human body.
- They are composed of glycerol and three fatty acid molecules.
- Triglycerides are obtained from dietary fats and are also synthesized in the liver from carbohydrates.
- They serve as an important energy source for the body.
- Excess triglycerides are stored in adipose tissue.
- Serum triglyceride estimation is an important part of lipid profile analysis.
- It helps assess lipid metabolism and cardiovascular risk.
- Increased serum triglycerides are associated with hyperlipidemia, diabetes mellitus, obesity, and cardiovascular disease.
- Very high triglyceride levels may increase the risk of pancreatitis.
Principle
- Serum triglycerides are estimated by enzymatic GPO-POD method.
- The reaction occurs in several enzymatic steps.
First Reaction
- Triglycerides are hydrolyzed by lipoprotein lipase (LPL).
- Glycerol and free fatty acids are produced.
- Triglycerides + H₂O → Glycerol + Free fatty acids
Second Reaction
- Glycerol reacts with ATP in presence of glycerol kinase (GK).
- Glycerol-3-phosphate is formed.
- Glycerol + ATP → Glycerol-3-phosphate + ADP
Third Reaction
- Glycerol-3-phosphate is oxidized by glycerol phosphate oxidase (GPO).
- Hydrogen peroxide is formed.
- Glycerol-3-phosphate + O₂ → Dihydroxyacetone phosphate + H₂O₂
Fourth Reaction
- Hydrogen peroxide reacts with 4-aminoantipyrine and 4-chlorophenol in presence of peroxidase (POD).
- A red colored quinoneimine dye is formed.
- H₂O₂ + 4-AAP + 4-Chlorophenol → Quinoneimine dye + H₂O
Principle of Measurement
- Intensity of red color formed is directly proportional to triglyceride concentration.
- Absorbance is measured at 505 nm.
Specimen
Sample Type
- Serum is preferred specimen
- Plasma can also be used
- EDTA plasma acceptable
- Heparin plasma acceptable
Precautions
- Use non-hemolyzed sample
- Fresh fasting sample preferred
- Avoid contaminated specimen
Stability
- 2 days at 20–25°C
- 7 days at 4–8°C
- 1 year at −20°C
Reagents
Reagent 1
- Good’s buffer (pH 7.2)
- 4-Chlorophenol
- Magnesium ions
- ATP
- Glycerol kinase
- Peroxidase
- Lipoprotein lipase
- Glycerol-3-phosphate oxidase
- 4-Aminoantipyrine
Materials Required
- Test tubes
- Micropipette
- Pipette tips
- Colorimeter / semi-auto analyzer
- Cuvette
- Timer
- Triglyceride reagent kit
Procedure
| Components | Blank | Standard | Test |
|---|---|---|---|
| Reagent | 1.0 ml | 1.0 ml | 1.0 ml |
| Distilled water | 10 µL | — | — |
| Standard | — | 10 µL | — |
| Sample | — | — | 10 µL |
Incubation
- Mix properly
- Incubate at 37°C for 5–10 minutes
Reading
- Measure absorbance of test and standard against blank
- Read at 505 nm
Calculation
Formula
Triglycerides (mg/dL) = Absorbance of Test / Absorbance of Standard × Standard concentration
Unit Conversion
- mg/dL × 0.0113 = mmol/L
Normal Reference Values
| Category | Value |
|---|---|
| Normal | < 150 mg/dL |
| Borderline High | 150 – 199 mg/dL |
| High | 200 – 499 mg/dL |
| Very High | > 499 mg/dL |
Clinical Significance
Increased Triglycerides (Hypertriglyceridemia)
- Hypertriglyceridemia means increased serum triglyceride level above normal range.
- Persistent elevation increases cardiovascular risk and may cause serious metabolic complications.
Hyperlipidemia
- Triglycerides rise in different types of hyperlipidemia.
- Excess lipoproteins circulate in blood causing lipid imbalance.
Clinical Importance
- common finding in dyslipidemia
- requires lipid profile monitoring
Diabetes Mellitus
- Diabetes is a major cause of increased triglycerides.
- Insulin deficiency or insulin resistance reduces lipid metabolism.
- More triglycerides remain in circulation.
Clinical Importance
- poor diabetic control often causes hypertriglyceridemia
- increases cardiovascular complications
Obesity
- Obesity increases triglyceride synthesis in the liver.
- Excess calorie intake converts into triglycerides.
Clinical Importance
- common in metabolic syndrome
- associated with insulin resistance
Cardiovascular Disease
- High triglycerides are recognized as an important cardiovascular risk factor.
- Elevated triglycerides contribute to atherosclerosis.
May Lead To
- coronary artery disease
- myocardial infarction
- stroke
Clinical Importance
- triglyceride monitoring helps assess cardiac risk
Atherosclerosis
- Excess triglyceride-rich lipoproteins contribute to plaque formation in arteries.
Effects
- narrowing of blood vessels
- reduced blood flow
- vascular damage
Nephrotic Syndrome
- Nephrotic syndrome causes marked triglyceride elevation.
- Liver increases lipoprotein production because of protein loss.
Clinical Importance
- common biochemical finding in nephrotic syndrome
Hypothyroidism
- Reduced thyroid hormone decreases lipid metabolism.
- Triglycerides accumulate in blood.
Clinical Importance
- often associated with raised cholesterol also
Liver Disease
- Some liver disorders alter triglyceride metabolism.
Seen In
- fatty liver
- alcoholic liver disease
Pancreatitis
- Very high triglycerides may cause acute pancreatitis.
- Usually seen when triglycerides are markedly elevated.
Clinical Importance
- medical emergency when very high
Alcohol Consumption
- Alcohol increases hepatic triglyceride synthesis.
Clinical Importance
- chronic alcohol intake causes hypertriglyceridemia
Familial Hypertriglyceridemia
- Genetic disorders may produce persistent high triglycerides.
Clinical Importance
- early cardiovascular risk
- family screening may be required
Drug-Induced Hypertriglyceridemia
Drugs Causing Increase
- corticosteroids
- oral contraceptives
- beta blockers
Decreased Triglycerides
- Low triglycerides are less common but may indicate nutritional or metabolic problems.
Malnutrition
- Poor nutritional intake reduces fat availability.
Hyperthyroidism
- Increased metabolism lowers triglyceride concentration.
Malabsorption Syndrome
- Fat absorption decreases in intestinal disease.
Clinical Importance
- low triglycerides may suggest absorption defect
Diagnostic Importance
- Serum triglycerides are essential in lipid profile interpretation.
Clinical Uses
- assesses lipid metabolism
- evaluates cardiovascular risk
- detects metabolic syndrome
- monitors lipid lowering therapy
Monitoring Importance
- Follow-up of hyperlipidemia treatment
- Monitoring diabetic patients
- Assessing dietary control
- Monitoring cardiovascular prevention
Relation with Other Lipid Parameters
- Triglycerides should always be interpreted with:
- total cholesterol
- HDL cholesterol
- LDL cholesterol
Clinical Importance
- combined lipid abnormality increases cardiovascular risk
Prognostic Importance
- Persistent high triglycerides suggest increased long-term metabolic and cardiovascular risk
