Estimation of Serum Triglycerides

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Introduction

  1. Triglycerides are esters derived from glycerol and three fatty acids, serving as the primary storage form of fat in humans and animals.
  2. They are transported in the bloodstream as part of lipoprotein particles, including very low-density lipoproteins (VLDL) and chylomicrons.
  3. Accurate measurement of serum triglyceride levels is crucial for assessing an individual’s lipid profile and risk for cardiovascular and metabolic diseases.
  4. Biochemical determination of serum triglycerides involves enzymatic and colorimetric methods, which provide reliable and reproducible results.
  5. Factors such as fasting status, metabolic rate, and diet influence triglyceride levels, making it vital to standardize testing conditions for accuracy.
  6. This article explores the methods, principles, sample handling, reagents, procedures, calculations, normal reference ranges, and clinical significance of triglyceride determination.

Principle

Triglycerides are hydrolyzed by lipase into glycerol and fatty acids.

Enzymatic Reaction Sequence

Triglycerides  →  Lipase →  Glycerol  +  Fatty Acids

Then glycerol undergoes further reactions to produce hydrogen peroxide, which reacts with chromogen to form a colored compound.

H2O2  +  Chromogen  →  Peroxidase   →  Colored Complex

Measurement

  • Color intensity is proportional to triglyceride concentration
  • Measured by spectrophotometer

Reagent 

  • Reagent: Triglycerides reagent 
    • Lipase
    • Glycerol kinase
    • Glycerol phosphate oxidase
    • Peroxidase
    • Chromogen buffer
  • Triglycerides Standard: 200 mg/dl (2.25 mmol/L)

Sample Collection and Handling

  1. Sample Type:
    • Serum or plasma is collected in a plain or heparinized tube.
    • EDTA or fluoride anticoagulants are not recommended as they may interfere with enzymatic reactions.
  2. Patient Preparation:
    • A 12-hour fasting period is required to minimize postprandial lipemia.
    • Water is allowed during fasting, but no other drinks or food should be consumed.
  3. Storage:
    • Serum samples should be analyzed promptly.
    • If delayed, samples can be stored at 2–8°C for up to 48 hours or frozen at -20°C for longer storage.

Procedure

Test Standard Blank
Reagent, ml 1 ml 1 ml 1 ml
Sample, ml 0.010 ml – –
Standard, ml – 0.010 ml –
Distilled water – – 0.010ml

Mix well and incubate for 5 mins. at 37°C (or 10 mins. at 20 – 25° C). Measure the absorbance of Sample (AT) and Standard (AS) against reagent blank at 505 nm

Sample Dilutions

This method is linear up to a concentration of 1300 mg/dL.  Dilute samples above this concentration 1:1 with 0.9% saline  Repeat assay. Multiply the result by 2.

Calculation

Calculate triglyceride concentration using the formula:

Triglyceride Concentration (mg/dL) = Absorbance of Sample /Absorbance of Standard × Concentration of Standard (mg/dl)

Normal Range

The reference range for serum triglycerides varies slightly depending on the laboratory and population studied. Typical adult reference ranges are:

  • Normal: <150 mg/dL (1.7 mmol/L)
  • Borderline High: 150–199 mg/dL (1.7–2.2 mmol/L)
  • High: 200–499 mg/dL (2.3–5.6 mmol/L)
  • Very High: ≥500 mg/dL (≥5.6 mmol/L)

 

Clinical Significance

Increased Serum Triglycerides (Hypertriglyceridemia)

Elevated serum triglyceride levels are commonly seen in conditions associated with increased fat synthesis, impaired lipid utilization, or defective lipoprotein metabolism.

Common causes include:

  • Diabetes Mellitus, especially when poorly controlled, due to increased mobilization of fatty acids and reduced insulin action
  • Obesity, because excess adipose tissue increases triglyceride production
  • High carbohydrate diet, which promotes hepatic triglyceride synthesis
  • Excess alcohol intake, which stimulates fatty acid formation in the liver
  • Hypothyroidism, due to reduced lipid metabolism
  • Nephrotic syndrome, because of altered lipoprotein metabolism
  • Chronic liver disease, where fat metabolism becomes disturbed
  • Pregnancy, due to hormonal influence on lipid metabolism
  • Familial hypertriglyceridemia, an inherited disorder of lipid metabolism

Clinical importance of elevated triglycerides

  • Increased risk of Atherosclerosis due to abnormal lipoprotein accumulation
  • Higher chance of coronary artery disease and cardiovascular events
  • Increased risk of Acute Pancreatitis when triglyceride levels become markedly elevated
  • Frequently associated with metabolic syndrome and insulin resistance
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Decreased Serum Triglycerides

Low triglyceride levels are less common but may indicate reduced fat absorption or increased metabolic consumption.

Causes include:

  • Malnutrition
  • Malabsorption syndrome
  • Hyperthyroidism
  • Chronic debilitating illness
  • Low-fat diet

Clinical importance of low triglycerides

  • May indicate poor nutritional status
  • Suggests impaired intestinal absorption of fat
  • Can occur in increased metabolic states

Role in Lipid Profile Assessment

Serum triglycerides are routinely measured along with:

  • Total cholesterol
  • HDL cholesterol
  • LDL cholesterol

This combined assessment helps evaluate cardiovascular risk more accurately.

Importance in Preventive Medicine

Regular triglyceride testing is important in patients with:

  • Obesity
  • Diabetes
  • Hypertension
  • Family history of heart disease

MCQs

1. Triglycerides are chemically composed of:

A. One glycerol and one fatty acid
B. One glycerol and two fatty acids
C. One glycerol and three fatty acids
D. Three glycerol and one fatty acid

Answer: C. One glycerol and three fatty acids

2. Triglycerides are mainly stored in:

A. Muscle protein
B. Adipose tissue
C. Bone marrow
D. Plasma proteins

Answer: B. Adipose tissue

3. Serum triglycerides are mainly transported in:

A. Albumin
B. Hemoglobin
C. Lipoproteins
D. Globulins

Answer: C. Lipoproteins

4. The routine laboratory method for triglyceride estimation is:

A. Titrimetric method
B. Enzymatic colorimetric method
C. Gravimetric method
D. Electrophoresis

Answer: B. Enzymatic colorimetric method

5. The first enzyme acting in triglyceride estimation is:

A. Peroxidase
B. Lipase
C. Catalase
D. Urease

Answer: B. Lipase

6. Lipase hydrolyzes triglycerides into:

A. Cholesterol and glycerol
B. Glycerol and fatty acids
C. Glucose and fatty acids
D. Amino acids

Answer: B. Glycerol and fatty acids

7. The sample required for triglyceride estimation is:

A. Plasma only
B. Serum
C. Whole blood
D. CSF

Answer: B. Serum

8. Fasting required before triglyceride estimation is:

A. 2 hours
B. 4 hours
C. 10–12 hours
D. 24 hours

Answer: C. 10–12 hours

9. Postprandial increase in triglycerides is due to:

A. HDL increase
B. Chylomicrons
C. LDL decrease
D. Albumin increase

Answer: B. Chylomicrons

10. Normal serum triglyceride level is:

A. Less than 150 mg/dL
B. Less than 300 mg/dL
C. Less than 500 mg/dL
D. Less than 50 mg/dL

Answer: A. Less than 150 mg/dL

11. Borderline high triglycerides are:

A. 50–100 mg/dL
B. 150–199 mg/dL
C. 250–300 mg/dL
D. 400–500 mg/dL

Answer: B. 150–199 mg/dL

12. Very high triglycerides are:

A. Above 500 mg/dL
B. Above 100 mg/dL
C. Above 200 mg/dL
D. Above 300 mg/dL

Answer: A. Above 500 mg/dL

13. Elevated triglycerides increase risk of:

A. Anemia
B. Pancreatitis
C. Leukemia
D. Asthma

Answer: B. Pancreatitis

14. One major disease associated with hypertriglyceridemia is Diabetes Mellitus

A. Diabetes mellitus
B. Tuberculosis
C. Malaria
D. Typhoid

Answer: A. Diabetes mellitus

15. The colored compound in triglyceride estimation is measured by:

A. Microscope
B. Spectrophotometer
C. Centrifuge
D. pH meter

Answer: B. Spectrophotometer

16. Peroxidase acts on:

A. Fatty acid
B. Hydrogen peroxide
C. Glucose
D. Cholesterol

Answer: B. Hydrogen peroxide

17. Triglycerides are mainly synthesized in:

A. Liver
B. Kidney
C. Brain
D. Spleen

Answer: A. Liver

18. A fasting sample is preferred because:

A. Protein rises
B. Lipemia interferes
C. Hemoglobin falls
D. Urea increases

Answer: B. Lipemia interferes

19. Hypertriglyceridemia commonly occurs in:

A. Starvation
B. Obesity
C. Dehydration
D. Fever

Answer: B. Obesity

20. Low triglycerides may occur in:

A. Hyperlipidemia
B. Malnutrition
C. Diabetes
D. Obesity

Answer: B. Malnutrition

21. Triglycerides are neutral:

A. Carbohydrates
B. Proteins
C. Fats
D. Vitamins

Answer: C. Fats

22. Standard solution is used for:

A. Hemolysis
B. Calibration
C. Centrifugation
D. Dilution

Answer: B. Calibration

23. Glycerol kinase converts glycerol into:

A. Glycerol phosphate
B. Fatty acid
C. Acetone
D. Cholesterol

Answer: A. Glycerol phosphate

24. Triglycerides are major source of:

A. Protein
B. Energy
C. Vitamins
D. Minerals

Answer: B. Energy

25. Excess alcohol causes:

A. Low triglycerides
B. High triglycerides
C. No effect
D. Low cholesterol

Answer: B. High triglycerides

26. Triglycerides are part of:

A. Lipid profile
B. CBC
C. LFT
D. KFT

Answer: A. Lipid profile

27. High triglycerides are associated with:

A. Atherosclerosis
B. Cataract
C. Anemia
D. Jaundice

Answer: A. Atherosclerosis

28. Enzymatic estimation is based on:

A. Color intensity
B. Weight
C. Smell
D. Conductivity

Answer: A. Color intensity

29. Triglycerides are transported mainly in:

A. HDL
B. LDL
C. VLDL
D. Albumin

Answer: C. VLDL

30. A milky serum sample suggests:

A. Hypoglycemia
B. Lipemia
C. Hemolysis
D. Dehydration

Answer: B. Lipemia

31. The end product measured is:

A. Blue color
B. Colored complex
C. Gas formation
D. Precipitate

Answer: B. Colored complex

32. Increased triglycerides may cause:

A. Fatty liver
B. Anemia
C. Leukopenia
D. Hypotension

Answer: A. Fatty liver

33. Triglycerides are esters of:

A. Glycerol
B. Cholesterol
C. Protein
D. Amino acid

Answer: A. Glycerol

34. Severe hypertriglyceridemia may cause Acute Pancreatitis

A. Acute pancreatitis
B. Gastritis
C. Arthritis
D. Hepatitis

Answer: A. Acute pancreatitis

35. Hypothyroidism causes:

A. Low triglycerides
B. High triglycerides
C. No change
D. Low protein

Answer: B. High triglycerides

36. Spectrophotometric reading depends on:

A. Light absorption
B. Smell
C. Heat
D. pH

Answer: A. Light absorption

37. The best sample condition is:

A. Hemolyzed
B. Fasting
C. Lipemic
D. Clotted

Answer: B. Fasting

38. Triglycerides belong to:

A. Protein metabolism
B. Lipid metabolism
C. Mineral metabolism
D. Vitamin metabolism

Answer: B. Lipid metabolism

39. Elevated triglycerides commonly occur in metabolic syndrome:

A. True
B. False

Answer: A. True

40. Glycerol phosphate oxidase produces:

A. Oxygen
B. Hydrogen peroxide
C. Carbon dioxide
D. Nitrogen

Answer: B. Hydrogen peroxide

41. Hypertriglyceridemia may be familial:

A. True
B. False

Answer: A. True

42. Triglycerides are affected by recent meal:

A. True
B. False

Answer: A. True

43. Lipase is:

A. Protein enzyme
B. Lipid enzyme
C. Fat hydrolyzing enzyme
D. Carbohydrate enzyme

Answer: C. Fat hydrolyzing enzyme

44. Triglycerides increase during pregnancy:

A. True
B. False

Answer: A. True

45. Low triglycerides occur in hyperthyroidism:

A. True
B. False

Answer: A. True

46. Serum triglycerides help assess cardiovascular risk:

A. True
B. False

Answer: A. True

47. Triglycerides are measured in:

A. mg/dL
B. g/L
C. mmol only
D. IU

Answer: A. mg/dL

48. High carbohydrate intake increases triglycerides:

A. True
B. False

Answer: A. True

49. Lipemic serum interferes with:

A. Accuracy
B. Taste
C. Smell
D. Shape

Answer: A. Accuracy

50. Triglycerides are important in preventive medicine:

A. True
B. False

Answer: A. True

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