cholesterol in serum/plasma

Indications

• assessment of cardiovascular risk factors
  • see lipid panel for screening intervals

Reference interval

• 150-250 mg/dL (distinguish from desirable)

 target        value               SI units
  desirable:   < 200 mg/dL         (< 5.18 mmol/L)*
  borderline:    200 - 239 mg/dL   (5.18 - 6.19 mmol/L)
  high:        > 240 mg/dL         (> 6.22 mmol/L)

* mg/dL -> mmol/L, multiply by 0.0259

Principle

The Kodak Ektachem Clinical Chemistry Slide (CHOL) quantitatively measures cholesterol in serum or plasma. Cholesterol is a Colorimetric-Test procedure.

The Kodak Ektachem Clinical Chemistry Slide (CHOL) is a dry, multilayered analytical element coated on a clear polyester support.

A 10 uL drop of sample is deposited on the slide. The isotropically porous spreading layer evenly distributes the sample.

The surfactant in the spreading layer aids in dissociating the cholesterol & cholesterol esters from lipoprotein complexes present in the sample. Hydrolysis of the cholesterol esters to cholesterol is catalyzed by cholesterol ester hydrolase & the cholesterol is then oxidized in the presence of cholesterol oxidase to form cholesterone & hydrogen peroxide. Finally, hydrogen peroxide oxidizes a triarylimidazole leuco dye in the presence of peroxidase to generate a colored dye. The density of dye formed is proportional to the cholesterol concentration present in the sample & is measured by reflectance spectrophotometry. Assay time is approximately five minutes & assay temperature is 37 C. The assay wavelength is 540 nm.

The reactions involved include:

                     cholesterol
                      esterase
cholesterol esters   ----------->     cholesterol + fatty acids

                     cholesterol
                      oxidase
cholesterol  + O2    ------------>   cholest-4-ene-3-one + H2O2

                     Peroxidase
H2O2 + leuco dye     ------------>   Dye  + H2O

Clinical significance

Cholesterol is present in tissues & in plasma lipoproteins either as cholesterol or as cholesterol esters bound to proteins. Cholesterol is an essential structural component of cell membranes and the outer layer of plasma lipoproteins & is the precursor of all steroid hormones, including sex & adrenal hormones, bile acids, & vitamin D.

Cholesterol measurements are used to evaluate the risk of developing coronary artery occlusion, atherosclerosis, myocardial infarction, & cerebrovascular disease. Coronary atherosclerosis correlates with a high cholesterol level. Cholesterol concentrations are increased in primary hypercholesterolemia, secondary hyperlipoproteinemia including nephrotic syndrome, primary biliary cirrhosis, hypothyroidism, & in some cases diabetes mellitus. Low cholesterol concentrations may be found in malnutrition, malabsorption, advanced malignancy, & hyperthyroidism. Serum cholesterol values depend on many factors including age & gender.

The concentration of cholesterol obtained within 24 hours of onset acute myocardial infarction reflect preinfarct levels, but after 24 hours significantly decline. In fact cholesterol serum levels drop with any acute injury or illness. 4 weeks should be allowed after recovery before assessing serum cholesterol levels.

Lowering of total cholesterol & LDL cholesterol to levels within NCEP guidelines reduces coronary artery disease related deaths in men & women. Benefits in the young & the elderly have not yet been demonstrated (20 > age > 75). The association between serum cholesterol & cardiovascular disease decreases with age. Higher serum cholesterol levels are associated with lower non-cardiovascular mortality in the elderly

Increased serum cholesterol since age 40 years associated with diminished risk of cognitive impairment in elderly 85-94 years, but not in those 75-84 years of age

Total serum cholesterol in persons < 50 years of age are directly related with 30-year overall & cardiovascular mortality, Overall mortality increases 5% & cardiovascular mortality 9% for each 10 mg/dL serum cholesterol.

After age 50 years there is no increase in overall mortality with either high or low serum cholesterol levels. There is an association between decreasing serum cholesterol & mortality in persons > 50 years of age.

New US Preventive Services Task Force recommendations (2001) sets no upper limit to age for routine screening for lipid disorders. Total cholesterol plus HDL cholesterol is recommended for screening purposes.

* All cause mortality, after adjustment for chronic disease

Increases

• see hypercholesterolemia
• pharmaceutical agents:
  • in vivo effects
    • ACTH, bile salts, chlorpromazine
  • chemical interferences
    • bromide

Decreases

• acute disease, trauma
• chronic disease
• pharmaceutical agents:
  • in vivo effects
    • heparin, thyroxines, HMG CoA reductase inhibitors, nicotinic acid

Specimen

The recommended specimen is 10 uL of serum or plasma. Collect the specimen by standard venipuncture technique. Heparin or EDTA may be used as an anticoagulant for plasma specimens. No special patient preparation is necessary. Special Precautions: Refrigerate specimens if analysis is not performed immediately. Freeze for long-term storage or shipment. Specimens stored at refrigerator or freezer temperatures are stable longer; however, repeated freeze/thaw cycles may result in decreased cholesterol results.

Minimum sample size is 0.5 milliliter;with an optimum size of 1.0 milliliter or larger.

Dilute grossly lipemic samples & samples with cholesterol values above the analyzer dynamic range with one part Kodak Ektachem Solution (7%BSA)/Bovine Serum Albumin & reanalyze. Multiply results by the dilution factor to obtain the original sample's cholesterol value. The dynamic range is 50 - 325 mg/dL.

Interferences

• Preliminary data indicated that hemolysis, icterus and lipemia do not interfere with this method.
• Total protein concentrations of 10 g/dL have caused a decrease of 18 mg/dL at cholesterol levels of 250 mg/dL.

More general terms

• cholesterol in body fluid
• liver (function) tests (LFT, liver panel, hepatic function panel)

More specific terms

• cholesterol non-esterfied in serum/plasma

Additional terms

• cholesterol
• hypercholesterolemia
• lipid panel (fasting lipid panel, FLP)

Component of

• lipid panel (fasting lipid panel, FLP)
• cholesterol ester/cholesterol total in serum/plasma
• cholesterol/apolipoprotein B in serum/plasma
• cholesterol/phospholipid in serum/plasma
• cholesterol/triglyceride in serum/plasma
• cholesterol total/cholesterol LDL in serum/plasma
• cholesterol LDL/cholesterol total in serum/plasma
• cholesterol total/cholesterol HDL in serum/plasma
• cholesterol HDL/cholesterol total in serum/plasma
• tocopherol/cholesterol in serum/plasma
• chronic kidney disease panel