Cholesterol measurement

Baseline is a common clinical concept. You might hear your physician say, Let s get a baseline cholesterol reading for you. The idea behind a baseline measurement is to determine the state of a patient before some expected event so that a subsequent comparison to that state can be made. For instance, you and your physician may want to get a baseline cholesterol reading early in life, as cholesterol typically increases with age. In clinical trials, you want to obtain a baseline measurement before a medical intervention to see what kind of effect the intervention had. Usually, the baseline value is the last reading prior to medical intervention. The following figure illustrates this concept for cholesterol measurements ... 

Cholesterol Measurement Date Date of Initial Therapeutic Intervention... 

If the cholesterol measurement is non-missing and was taken within the five days prior to drug dosing, then the cholesterol values are valid values for baseline. Note that because the cholesterol data are sorted chronologically (as mentioned in note 1), the last non-missing value within the five-day window is carried forward in time as... 

Total cholesterol measurements include the free and esterlfied fractions. 

The chemical methods for the quantitation of cholesterol measure total cholesterol, i.e. free and esterified, and so a digitonin precipitate must be prepared if free cholesterol is to be measured. Enzymic methods do not measure the esters and a hydrolysis stage, either chemical or enzymic (using cholesterol ester hydrolase, EC 3.1.1.13), is necessary for the measurement of total cholesterol. 

Although both LDL and HDL are primarily cholesterol particles, most of the cholesterol measured in the blood is assodated with LDL. The normal role of LDL is to deliver cholesterol to tissues for biosynthesis. When a cell is repairing membrane or dividing, the cholesterol is required for membrane synthesis. Bile acids and salts are made from cholesterol in the liver, and many other tissues require some cholesterol for steroid synthesis. As shown in Figure 1-15-6, about 80% of LDL are picked up by hepatocytes, the remainder by peripheral tissues. ApoB-100 is the only apoprotein on LDL, and endocytosis of LDL is mediated by apoB-100 receptors (LDL receptors) clustered in areas of cell membranes lined with the protdn clathrin. 

A detailed report in the USA showed that by reducing the uncertainty of cholesterol measurement from 24% to 5%, the USA economy saved, every year, 100 million US dollars. 

To give an example, if a producer prepares 4000 vials from a batch of human serum, to be used as certified reference material for cholesterol measurements, it is neither practical nor realistic to measure the cholesterol content in all the 4000 vials. The measurements will be performed only on a number of vials. This will be discussed in more detail below. 

Total blood cholesterol 200 to 239 mg/dL HDL 35 mg/dL or more and less than 2 risk factors, provide information on dietary modification, physical activity, and risk factor reduction reevaluate in 1 to 2 years, repeat total and HDL cholesterol measurements, and reinforce nutrition and physical activity education. HDL less than 35 mg/dL or at least 2 risk factors, analyze lipoprotein base further action on LDL levels. 

A population of patients in a cholesterol lowering study have total cholesterol measured at baseline. Assume that total cholesterol is normally distributed with mean, p = 7.0 mmol/1 and standard deviation, s = 1.1 mmol/1 so that the variance is 1.21 (= 1.1 ). We write this as N(7.0, 1.21). For historical reasons we put the variance as the second parameter here. Under these assumptions the following results hold ... 

In this experiment, two cholesterol measurements will be made (1) total serum cholesterol and (2) HDL serum cholesterol, the amount of cholesterol associated with the HDL fraction. The following relationship leads to an estimate of LDL (Equation El 1.7). 

Gas-liquid chromatography (GLC) alditol acetates, neutral sugar determination, 721 -732 cholesterol measurement, 453-456, 460-462 (tables)... 

Reversed-phase high-performance liquid chromatography (RP-HPLC), cholesterol measurement, 456-458 Rhamnogalacturonanas, 735 Rice bran oil, tocopherols/tocotrienols in, 488 (figs.)... 

Bioanalyzer can be considered another version of commercial biosensors for off-line analysis. It was developed to have capabilities of complete analysis, short response time, specificity, and sensitivity that allows a quick clinical test. Abbott Vision, Boehringer-Mannheim Reflectron, and Kodak Ektachem DT60 (IBI Biolyzer is the new name) are used for cholesterol measurement in doctors offices. Bioanalyzer consists of biological and transducing component that are not physically connected. The uniqueness of this separation provides the versatility of analysis, i.e., use of disposable and different biological component for multi-components measurements. In authors laboratory, Kodak Ektachem DT60 was used successfully to determine cholesterol in some food matrices as well as in off-line process control. The analysis time was only 10 minutes compared to 1-2 days for the GC and HPLC methods. Complicated... 

National Institutes of Health (1990) Recommendations for improving cholesterol measurement a report from the Laboratory Standardization Panel of the National Cholesterol Education Program. Bethesda, Md. NIH publication no 90 2964... 

NCCLS (1999) Preparation and validation of commutable frozen human serum pools as secondary reference materials for cholesterol measurement procedures. NCCLS, Wayne, Pa. NCCLS document C37-A... 

E300 Warnick, G.R., Lum, C. and Knopp, R.H. (1986). Kodak Ektachem HDL kit evaluated for HDL cholesterol measurements with the DT-60 instrument. Clin. Chem. 32, 1988. 

E503 Bateson, J.E., Artiss, J.D. and Zak, B. (1989). Cholesterol measurement in grossly lipemic specimens. Clin. Chem. 35, 1072, Abstr. 33. 

Carleton, R.A. (1989). Performance characteristics of a blood cholesterol measuring instrument used in screening programs. Public Health Rep. 104, 266 270. 

E546 McManus, B.M., Toth, A.B., Engel, J.A., Myers, G.L., Naito, H.K., Wilson, J.E. and Cooper, G.R. (1989). Progress in lipid reporting practices and reliability of blood cholesterol measurement in clinical laboratories in Nebraska. JAMA 262, 83-88. 

E595 Broughton, P.M.G., Bullock, D.G. and Cramb, R. (1990). Improving the quality of plasma cholesterol measurements in primary care. Scand. J. Clin. Lab. Invest. 50, Suppl. 198, 43 8. 

EN24 Fahey, P.J., Lott, J.A., Peet, G.M. and Crowley, L.E. (1991). Accuracy and precision of HDL cholesterol measurements using an office chemistry analyzer. J. Fam. Pract. 32, 382-386. 

ENlOl Gregory, L.C., Duh, S.-H. and Christenson, R.H. (1992). An evaluation of total cholesterol measurements by desk-top analyzers. Clin. Chem. 38, 1037, Abstr. 439. 

EN104 Hartley, T.F. and David, R.S. (1992). Cholesterol measurements in patients sera stored at 4 or -20°C for 24 h before analysis with a Kodak Ektachem 700 analyzer. Clin. Chem. 38, 1191-1192. 

ENl 15 Malavasi, B., Catapano, A., Galli, G. and Franzini, C. (1992). A collaborative trial for the evaluation of blood cholesterol measurement in clinical laboratories in Italy. Europ. J. Clin. Chem, Clin. Biochem. 30, 157-161. 

R107 Kinlay, S. (1988). Comparison ofReflotron and laboratory cholesterol measurements. Med. J. Aust, 149, 126-129. 

R127 Sedor, F.A., Holleman, C.M., Heyden, S. and Schneider, K.A. (1988). Reflotron cholesterol measurement evaluated as a screening technique. Clin. Chem. 34, 2542-2545. 

RI3l Wones, R.G., Kerman, K.M., Stein, E.A., Meloy, N. and Hissa, D.C. (1988). Accuracy of Reflotron cholesterol measurements by lab technicians and nurses in 1006 adults. Circulation 78,11-383, Abstr. 1528. 

R145 Gubata, P. and Lefebvre, R.C. (1989). Comparison testing of lot to lot variance in the Reflotron dry reagent strip method of cholesterol measurement. Clin. Chem. 35, 1098, Abstr. 155. 

R149 Lefebvre, R.C., Lasater, T.H., McRinlay, S.M., Cans, R.M., Walker, N. and Carleton, R.A. (1989). Performance characteristics of a blood cholesterol measuring instrument used in screening programs. Public Health Rep. 104, 266-270. 

R174 Cramb, R., Florkowski, C.M., Lemon, M., Batki, A., Gaskin, C. and Broughton, P.M.G. (1990). Cholesterol measurement on Reflotron A capillary caution. Clin. Chem. 36, 954, Abstr. 17. 

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