Cholesterol (Serum Cholesterol)

Sample

1. The best sample is after 12 hours of fast and that is the morning sample.
2. The best sample is serum and separated within 2 hours of the collection.
3. This test may be done on Serum or Plasma (EDTA) but not oxalate, citrate, or fluoride.
4. The serum is stable at 4 °C for 5 to 7 days and 3 months at -20 °C.
5. Avoid freezing and thawing.
6. The result with EDTA plasma is 3% lower than serum.
7. Sample with Cholesterol above 500 mg/dL should be diluted.

Precautions

1. Try to separate serum or plasma from the cells within 2 hours.
2. The best sample is after 12 to 14 hours of fast.
3. Pregnancy may give a high level.
4. Drugs that may increase the level are anabolic steroids, corticosteroids, oral contraceptives, vitamin D, phenytoin, thiazide diuretics, and cyclosporin.
5. Drugs that may decrease the level are captopril, colchicine, erythromycin, isoniazid (INH), lovastatin, neomycin, bile salt binding agents, androgens, niacin, and nitrates.

Purpose of the test

1. Cholesterol level is estimated to determine the coronary artery disease risk.
2. This test may be needed to rule out hyperlipidemia.

Pathophysiology

1. Cholesterol is steroid alcohol with 27 carbon atoms.
   1. Cholesterol is present virtually in all cells and body fluids.
2. Cholesterol is absorbed in the diet and synthesized in the liver and gut.
   1. t is a precursor of steroid hormone, bile acids, sex hormones, and cellular membranes.
3. Cholesterol is present in the diet, mostly comes from the animal source, and absorbed by the gastrointestinal tract.
   1. Another source is endogenous like the liver and other tissues.
      1. All the cells have the ability to synthesize the cholesterol and 90% occur in the liver and intestines.
   2. Malnutrition will give low cholesterol formation.
4. Cholesterol level in the body:
   1. Cholesterol in the fasting serum is carried by three different lipoproteins. So the total sum of cholesterol is equal to the sum of these three components.
   2. Total cholesterol = HDL-cholesterol + VLDL-cholesterol + LDL-cholesterol
      1. The amount of cholesterol in the HDL fraction can be found by precipitating from the serum.
      2. The level of cholesterol in VLDL = triglycerides/5
         1. This formula works in the fasting sample and when the triglycerides are <400 mg/dL.
      3. LDL (cholesterol) = Total cholesterol mg/dL – HDL-cholesterol mg/dL – triglycerides mg/dl/5
5. Cholesterol changes in the body:
   1. There is day to day variation in the cholesterol level.
   2. This day to day variation may be in a person around 15%.
   3. An 8% difference can be found on the same day.
   4. There is a positional change in the level.
      1. The level may be decreased as much as 15% in the recumbent position.
   5. There is a low level in the hospitalized patient.
   6. Because these variations two samples must be tested for heart disease risk.
   7. In acute MI, there is a decreased level of cholesterol as much as 50% for 6 to 8 weeks.

6. Cholesterol absorption:
   1. The main source of cholesterol is diet.
   2. The cholesterol enters the intestine from the following sources:
      1. Food like egg yolk, meat, fat-diary products, and seafood, the average amount is 400 to 700 mg/day.
         1. Plant sterols (200 to 300 mg) are ingested daily. These are poorly absorbed.
      2. Bile, provide another fraction of cholesterol.
      3. Intestinal secretions and turn over of the intestinal mucosal cells are another source.
      4. Bile acids are detergents and are the most important factor affecting micelles formation.
         1. In the absence of bile acids, digestion, and absorption of the cholesterol and triglyceride are severely affected.
      5. Most absorption of the cholesterol takes place in the jejunum and ileum.
      6. When cholesterol enters the intestinal cells then it is packaged with triglycerides, phospholipids, apolipoprotein into large lipoprotein called chylomicrons.
      7. When there is an increased amount of fat in diet particularly triglycerides 98%, will result in more micelles formation which in turn allows more cholesterol to be solubilized and absorbed.

7. Cholesterol esterification: Cholesterol once formed enters the blood circulation.
   1. It is then esterified and combine with apoprotein and apolipoprotein and ultimately carried as a lipoprotein.
      1. Cholesterol esterification helps in the packing of the cholesterol into lipoproteins.
      2. Both dietary and synthesized cholesterol is converted to cholesteryl esters which are easily packed into lipoproteins.
      3. Esterification increases the lipid carrying capacity of the lipoproteins in plasma and prevents the toxicity effect of the cholesterol.
   2. 75% bound to LDL.
   3. 25% bound to HDL.

8. Biosynthesis of Cholesterol 
   1. 90% of the cholesterol synthesis takes place in the liver and gut.
   2. Cholesterol synthesis takes place in three stages.
   3. The starting molecule is acetate.
   4. All body cells have the ability to synthesize cholesterol from Acetyl-CoA.
   5. Knowing the endogenous synthesis of the cholesterol, drugs are developed which lower the cholesterol level like mevastatin, lovastatin, simvastatin, pravastatin, and atorvastatin, which will suppress the HMG-CoA reductase.

9. Cholesterol exists in two forms:
   1. Free cholesterol.
   2. Esterified cholesterol.
      1. 75 to 85% of the total cholesterol is in the form of esterified cholesterol.
         1. Cholesterol can be derived from a dietary source like meat, eggs, butter, and plants.
         2. 30 to 60% of the dietary cholesterol is absorbed.
         3. Once cholesterol is absorbed into the mucosal cells then it becomes part of the large micelle is called Chylomicron.
   3. Cholesterol found in:
      1. Chylomicron 2%.
      2. VLDL = 5 to 8%.
      3. LDL = 13%.
      4.  HDL = 6%.

3. 4. Cholesterol is a blood lipid ( fat ).
   5. Cholesterol is a normal part of RBC.
   6. Cholesterol, when increased, leads to atherosclerosis and is the main lipid.

6. 7. Cholesterol is the basic unit of hormone produced by adrenal glands, ovaries, and testes.
   8. cholesterol is needed for bile acids and cellular membranes.
   9. Cholesterol is transported in the circulation by carrier proteins.
      1. Cholesterol bound to high-density lipoprotein (HDL- cholesterol) is known as good cholesterol. This will prevent atherosclerosis.
      2. Cholesterol bound to low-density protein (LDL-cholesterol) is known as bad cholesterol and increases the chances of atherosclerosis.
      3. Also the same is the cholesterol bound to very-low-density lipoprotein (VLDL) is bad cholesterol.
   10. Increased Cholesterol level is associated with atherosclerosis and coronary vessel disease.

10. Cholesterol functions:
    1. It is needed for the formation of steroids, sex hormones, and bile acids.
    2. This is the part of cellular membranes.
    3. It gives the risk of heart diseases.

Normal

Source 1
Adult

1. The desired level to prevent coronary disease is < 200 mg/dl
2. Moderate risk is 200-239 mg/dl
3. High risk is > 240 mg/dl
4. CSF <0.5 mg/dl

Source 2

Sample	Male mg /dL	Female mg /dL
Cord blood	44 to 103	50 to 108
0 to 4 years	114 to 203	112 to 200
5 to 9 years	121 to 203	126 to 205
10 to 14 years	119 to 202	124 to 201
20 to 24 years	124 to 218	122 to 216
30 to 34 years	138 to 254	130 to 230
40 to 44 years	151 to 268	147 to 252
50 to 54 years	158 to 277	162 to 285
60 to 64 years	159 to 276	172 to 297
>70 years	144 to 265	173 to 280

•  To convert into SI unit x 0.0259 = mmol/L

Cholesterol and its relation to heart disease:

Children

1. Desirable level is < 170 mg/dl
2. Moderate risk is 170-199 mg/dl
3. High risk is > 200 mg/dl

• Above 240 mg/dL   =  needs treatment.
• Nowadays cardiology association recommends the level to be around 160 mg/dl.

Cholesterol mg/dL	Risk
<160	Very low
160 to 199	low risk
200 to 239	moderate risk
240 to 279	high risk
>280	very high risk

• There is no relation between the total cholesterol and heart disease risk according to the latest NHS research study.
  • https://www.nhs.uk/news/heart-and-lungs/study-says-theres-no-link-between-cholesterol-and-heart-disease/

ATP III (Adult treatment panel) recommendations are:

Total Cholesterol:

1. Desirable level = <200 mg/dL
2. Borderline level = 200 to 239 mg/dL
3. High Risk level = >240 mg/dL

Increased Cholesterol (Hypercholesterolemia):

1. Familial combined hyperlipidemia.
2. Hyperlipoproteinemia type, 1V, V.
3. Intra- and extrahepatic cholestasis.
4. Glomerulonephritis.
5. Nephrotic syndrome, and chronic renal failure.
6. Malignant neoplasm of pancreas and prostate.
7. Hypothyroidism.
8. Gout.
9. Diabetes mellitus.
10. Alcoholism.
11. Glycogen storage diseases type 1 (Von Gierke disease).
12. Stress.
13. biliary cirrhosis.

Decrease Cholesterol (Hypocholesterolemia):

1. alpha-Lipoprotein deficiency.
2. Hepatocellular necrosis.
3. Malignant neoplasm of the liver.
4. Hyperthyroidism.
5. Malabsorption and malnutrition.
6. Severe acute illness.
7. Extensive burns.
8. Rheumatoid arthritis.
9. Cholesterol-lowering medications.

Prevention and Interpretation:

Total cholesterol <200 mg/dL	Check after 5 years
Total cholesterol 200 to 239 mg/dL	0 to 1 risk factor and no coronary disease. Needs diet control and repeat the test after one year.
Total cholesterol >240 mg/dL	Diet control and/or drugs intervention

Risk factors are:

1. Cigarette smoking.
2. Cerebrovascular disease.
3. Diabetes mellitus.
4. Hypertension.
5. The family history of coronary heart disease.
6. Sex as in male.
7. Overweight >30%
8. peripheral occlusive vascular disease.

Important:

• • There is variation in the level of cholesterol so take at least two samples.

 

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