Lipoprotein – Part 5 – Triglycerides (TG)

Sample

1. This is done ideally on the fasting serum of the patient. Venous blood is taken.
2. Fasting for 12 to 14 hours is required.
3. Plasma with EDTA can be used.
4. The sample is stable at 4 °C for 7 days and at -20 °C for 3 months.
5. If plasma is used then multiply the result by 1.03.

Precautions

1. Patients must have at least fasting for 12 hours.
2. If TG in male > 160  mg/dL and female > 135 mg/dL then two more samples should be done in next 6 to 8 weeks.
3. Intake of the fatty meal may increase the TG.
4. Alcohol intake increases TG.
5. In pregnancy, the TG level is raised.
6. Take H/O drubs like oral contraceptives and estrogen to increase the TG level.
7. Take H/O ascorbic acid, clofibrate, and colestipol to decrease the TG level.

Indication

1. This is done to evaluate the causes of atherosclerosis (Coronary artery disease).
2. This is done to evaluate the turbid serum (milky).
3. Triglyceride is part of the lipid profile.
4. Triglyceride advised in a patient with suspected fat metabolism disorder.

Pathophysiology                                                                                                                                                                                    

1. TG consists of three fatty acids + one molecule of glycerol by ester bond, so-called as Triglycerides.
   1.  Glycerol and fatty acids building block for TG.
   2. Three fatty acids  + one molecule of glycerol (ester bond)  =  Triglyceride
   3. TG is present in the blood and transported by the VLDL and LDL.

1. 2. Glucose must be present in the cells for the formation of TG.
   3. There is Triglyceride formation by the glycolytic pathway in the glucose catabolism.
   4. This triglyceride formation may be absent in case of:
      1. Fasting.
      2. Starvation.
      3. Uncontrolled diabetes mellitus.

2. TG when catabolized forms a small fraction of free fatty acid which appears in plasma bound to albumin.
   1. These nonesterified fatty acids after oxidation enter the Acetyl CoA cycle.
   2. The end result is water, CO2, and ATP which is the source of energy.
      

      Triglycerides catabolism

      

      Triglycerides and Its Fate

3. TG is the fat in the bloodstream.
   1. TG accounts for more than 90 % of the food intake and is 95% of the fat stored.
   2. TG is insoluble in water and these are the main glycerol ester.
4. TG is stored in adipose tissue as :
   1. Glycerol.
   2. Fatty acids.
   3. Monoglyceride.
5. The liver is the factory to converts all the above into triglycerides.
   

   Metabolism of Triglyceride in hepatocyte

6. One of the sources gives the following ratio of triglycerides in various fats.
   

   Composition of Triglyceride

7. TG are Transported and present in :
   1. 80 % are in VLDL.
   2. 15 % are in LDL.

8. TG is the source of energy.
9. When TG is high then starts depositing in fatty tissue.
10. Source of Triglyceride:
    1. Plants contain polyunsaturated fatty acids.
       1. Corn.
       2. Sunflower.
       3. Safflower.
    2. The animal source contains mostly saturated fatty acids and solid at room temperature.
11. The Fredrickson-levy classification method for hyperlipidemia:  Keep the plasma at 4 C refrigerate for 16 hours and then made an observation of the creamy layer at the top of turbidity.
    1. This can be completed by doing a lipid profile.

Normal Triglycerides

Source 1

Age	Male mg/dL	Female mg/dL
Cord blood	13 to 95	11 to 76
0 to 9 year	30 to 100	35 to 110
10 to 14 year	32 to 125	37 to 131
15 to 19 year	37 to 148	39 to 124
20 to 24 year	44 to 201	36 to 131
25 to 29 year	46 to 249	37 to 144
30 to 34 year	50 to 266	39 to 150
35 to 39 year	54 to 321	40 to 176
40 to 44 year	55 to 320	45 to 191
45 to 49 year	58 to 327	46 to 214
50 to 54 year	58 to 320	52 to 233
55 to 59 year	58  to 286	55 to 262
60 to 64 year	58 to 291	56 to 239
>65 year	55 to 260	60 to 240

• To convert into SI unit x 0.0113 = mmol/L
• Recommended cutoff point for evaluating triglyceridemia status:
  • Normal = <250 mg/dL
  • Borderline high = 250 to 500 mg/dL
  • Hypertriglyceridemic = >500 mg/dL
  • High risk for pancreatitis = >1000 mg/dL

Source 2

• Male Adult  = 40 to 160 mg /dL.
• Female Adult  = 35 to 135 mg /dL.

Children	Male  mg/dL	Female mg/dL
0 to 5 years	30 to 86	32 to 99
6 to 11 years	33 to 108	35 to 114
12 to 15 years	36 to 138	41 to 138
16 to 19 years	40 to 163	40 to 128 mg

Critical values are:

• Desirable = < 150 mg /dL.
• Borderline high = 150 to 199 mg /dL.
• High = 200 to 499 mg /dL.
• Very high = > 500 mg /dL.
• Critical value  >400 mg/dL

Triglycerides concentration according to the National cholesterol education program adult treatment panel (NECP-ATP II).

Concentration	Serum Triglyceride mg/dL
Normal	<200
Borderline	200 to 400
High	400 to 1000
Very high	>1000

Increased Triglycerides values are seen in:

1. Hyperlipidemia.
2. Hyperlipoproteinemia.
3. Nephrotic syndrome.
4. Liver diseases.
5. Alcoholism (alcoholic cirrhosis).
6. Diabetes Mellitus, uncontrolled.
7. Glycogen storage disease (Von Gierke disease).
8. Familial hypertriglyceridemia.
9. Hypothyroidism.
10. Gout.
11. Anorexia nervosa.
12. Down’s syndrome.
13. Myocardial infarction.

Decreased Triglycerides level is seen in:

1. Malnutrition.
2. Hyperthyroidism.
3. Congenital α-β- lipoproteinemia.
4. Malabsorption.

Management of Hypertriglyceridemia:

1. If Triglycerides is < 200 mg/dL then the person needs diet control and he should be advised to repeat triglyceride once a year.
2. If Triglycerides is 200 to 500 mg/dL then evaluate the patient with risk factors like:
   1. Diabetes mellitus
   2. Alcoholism
   3. Hypothyroidism
   4. Hypertension
   5. Hyperuricemia
   6. Medication like beta-blockers, Estrogen, corticosteroids, oral contraceptives.
   7. Diseases like kidney, pancreatitis.
      1. No above risk factors in a person need only diet control
      2. Positive above risk factors and family history in a person needs diet and medication
3. Critical value If triglyceride is >500 mg/dL in a person then these patients need diet control and medication.

Table showing the summary of characteristics of the lipoproteins

Characteristics	Chylomicron	HDL	LDL	VLDL
Size (diameter nm)	>70.0	4 to 10	19.6 to 22.7	25 to 70
Electrophoretic mobility	Origin	α – region	β – region	Pre – β region
Molecular weight	0.4 to 30 x 109	3.6 x 109	2.75 x 109	5 to 10 x 109
Synthesized in	Intestine	Intestine and liver	Intravascular	Liver and intestine
Composition by weight in %
Cholesterol esterified	5	38	49	11 to 14
Cholesterol unesterified	2	10	13	5 to 8
Triglycerides	84	9	11	44 to 60
Phospholipids	7	22	27	20 to 23
Proteins	2	21	23	4 to 11

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