Gerald R. Cooper

National Academy of Clinical Biochemistry Laboratory Medicine Practice Guidelines: Emerging Biomarkers for Primary Prevention of Cardiovascular Disease

BACKGROUND Heart disease and stroke continue to be the leading causes of death in the US. As a result, investigators continue to look for new and emerging biomarkers of disease risk. Because many of these emerging biomarkers are not as well documented as those of conventional lipid and lipoprotein risk factors, their value in clinical practice needs to be critically appraised and appropriate guidelines developed for their proposed use. CONTENT The National Academy of Clinical Biochemistry (NACB) convened a multidisciplinary expert panel to develop laboratory medicine practice guidelines for a selected subset of these emerging risk factors as applied in a primary prevention setting of heart disease and stroke. The NACB expert panel selected lipoprotein subclasses and particle concentration, lipoprotein(a), apolipoproteins A-I and B, high sensitivity C-reactive protein (hsCRP), fibrinogen, white blood cell count, homocysteine, B-type natriuretic peptide (BNP), N-terminal proBNP (NT-proBNP), and markers of renal function as biomarkers that fell within the scope of these guidelines. CONCLUSIONS Based on a thorough review of the published literature, only hsCRP met all of the stated criteria required for acceptance as a biomarker for risk assessment in primary prevention.

Distribution of triglyceride and total, LDL and HDL cholesterol in several populations: a cooperative lipoprotein phenotyping study.

Abstract Data on the distribution of triglyceride and total, LDL and HDL cholesterol are presented for age groups 40 yr and older. The populations represented came from Framingham, Albany, Honolulu, San Francisco, Evans County and Puerto Rico. They include white, Japanese and black persons and both sexes. Blood samples and lipid measurements were obtained after overnight fast by a common protocol as part of a cooperative study of lipoprotein phenotyping. Means, medians, standard deviations and 95th percentiles are given as well as intercorrelations among the various lipids. Average cholesterol levels ranged from 200 mg/dl (Puerto Rican men) to over 240 mg/dl (Framingham women). Average triglyceride levels ranged from less than 100 mg/dl (Evans County) to an average of 175 mg/dl (Japanese men). For men aged 50–69 triglyceride levels were higher in Puerto Rico than in Albany or Framingham, despite much lower levels of serum cholesterol. The 95th percentile for LDL cholesterol in age groups with at least 100 persons ranged from 196 to 209 mg/dl for men and between 221 and 228 mg/dl for women. The 95th percentile for triglyceride, however, varied greatly by age and population from as low as 249 mg/dl to as high as 451 mg/dl.

Black-white differences in serum lipids and lipoproteins in Evans County

Abstract The Evans County Cardiovascular Disease Survey has demonstrated a higher prevalence and incidence of coronary heart disease in white than in black men. Prior studies by us have disclosed similar associations of CHD with the risk factors of elevated blood pressure, serum cholesterol, and smoking in Evans County as have been reported elsewhere. The lower frequencies of CHD in black than in white males are present, controlling for the standard risk factors in univariate and in multivariate logistic risk function analyses. Black-white differences in total serum triglyceride and in cholesterol within lipoprotein fractions at identical total serum cholesterol levels are described in this report. Significantly higher LDL cholesterol and total triglycerides are present in whites, and higher HDL cholesterol was found in blacks in an age, sex, and total serum cholesterol matched comparison. The determinants of the black-white differences in lipid and lipoprotein fraction distributions are still to be elucidated, but in this sample, lipid differences are not explained by social characteristics, such as occupation and social class. The black-white lipoprotein fraction differences in Evans County are consistent with a negative, coronary risk factor role of elevated HDL cholesterol, which has been postulated based on other experimental and prevalence studies.

Standardization of Immunoassays for Measurement of High-Sensitivity C-reactive Protein. Phase I: Evaluation of Secondary Reference Materials

BACKGROUND Inflammation contributes to the development and progression of atherosclerosis, and C-reactive protein (CRP) can be used as a marker to assess risk for cardiovascular diseases. As variability among existing high-sensitivity CRP (hsCRP) assays can lead to misclassification of patients and hamper implementation of population-based medical decision points, standardization of hsCRP assays is needed. METHODS We evaluated five proposed secondary reference materials, including two diluted preparations of Certified Reference Material 470 (CRM470), two preparations of a serum-based material with recombinant CRP added, and one serum-based material with isolated CRP added. Twenty-one manufacturers participated in the comparison with 28 different assays. We examined imprecision, linearity, and parallelism with these materials and with fresh serum. RESULTS All materials had similar imprecision; CVs for the undiluted materials were 2.1-3.7%. None of the materials was linear across all assays. Each had between one and three cases of nonlinearity, with one preparation of CRM470 having the fewest cases of nonlinearity. Although none of the materials was parallel across all assays, the differences in slope from fresh serum were similar across all assays. CONCLUSIONS All materials performed similarly with regard to imprecision, linearity, and parallelism. As one preparation of CRM470 had slightly better characteristics than the other materials and because CRM470 had been certified previously as a reference material for the acute-phase reactant range, it will be used in the next phase to standardize hsCRP assays.

The combined effect of smoking and coffee drinking on LDL and HDL cholesterol.

Conflicting reports on the effect of smoking and coffee drinking on lipoproteins prompted us to study the combined effect of these two associated, widely prevalent habits in 361 persons randomly sampled from the Evans County cohort. Low-density lipoprotein (LDL) cholesterol levels were significantly higher among persons who smoked cigarettes and consumed five or more cups of coffee per day than among nonsmokers who abstained from coffee. Conversely, high-density lipoprotein (HDL) cholesterol was higher in persons who did not smoke or drink coffee than in coffee-consuming smokers. However, this trend was not statistically significant. Triglycerides and very low-density lipoprotein (VLDL) cholesterol were highest among smokers who drank five or more cups of coffee per day, but these differences did not reach statistical significance. Lipoprotein cholesterol levels were adjusted for age, sex and body mass. Smoking and coffee drinking interact in affecting LDL and total cholesterol, but coffee drinking alone did not appear to affect blood lipids.

Apolipoprotein A-I, A-II and C-II in black and white residents of Evans County.

Plasma levels of lipids, lipoprotein-cholesterol and three major apolipoproteins (ApoA-I, A-II and C-II) were studied in 318 black and white males and females randomly sampled in Evans County, Georgia. Black-white differences in lipid and lipoprotein-cholesterol concentrations were observed, with low-density fractions higher in whites and high-density fractions higher in blacks. Plasma levels of ApoA-I but not ApoA-II were higher in blacks than in whites and in females than in males. ApoC-II concentrations were lower in black than in white men and women. Black-white differences in atherogenic lipoprotein fractions were statistically explained (in the sense of association, not necessarily of causal process) by the differences in ApoC-II concentrations between the race groups. Black-white diflerences in antiatherogenic high-density lipoprotein-cholesterol were greater than statistically predicted by differences in ApoA lipoprotein levels. The findings are indicative of black-white differences in lipoprotein composition.

Traditional lipoprotein profile: clinical utility, performance requirements, and standardization☆

The lipid and lipoprotein parameters which are predominantly measured and effectively comprise the traditional lipoprotein profile include total cholesterol, high density lipoprotein (HDL) cholesterol, low density lipoprotein (LDL) cholesterol, and triglyceride. Total cholesterol is accepted as the initial entry point in a case finding approach such as that recommended by the National Cholesterol Education Program (NCEP). HDL cholesterol, known to be a strong inverse predicator of risk, is an additional measurement to total cholesterol to improve risk assessments. The evidence for triglyceride association remains mixed: although strong associations are found in some studies, the evidence as an independent risk factor is still incomplete. Triglyceride is therefore measured primarily for LDL estimation. Final classification and potential intervention is ultimately based on the measurement of LDL cholesterol. Reliability in the measurement of total cholesterol, HDL, LDL, and triglyceride is especially important if the uniform decision points established by the NCEP are to be properly implemented. Attention must be placed on controlling preanalytical sources of variation, which can account for as much as 60% of the total measurement variability. The major analytical source of error comes from matrix effects, which results in problems of proper analytical calibration. Instrument system calibration should be verified by a comparison with an accuracy base using fresh patient specimens. CDC has established a network of reference method laboratories to provide access to these lipid and lipoprotein accuracy bases.

Preanalytical, including biological, variation in lipid and apolipoprotein measurements

Since scientists recognized that preanalytical sources of variation often constitute more than 60% of the total variation in reported lipid measurements, they have been concerned about both the effects of these sources and ways to minimize their impact on lipid measurement. Sampling techniques, behavioral factors, metabolic disorders, and disease status are major preanalytical sources of variation. Lipid analysis of serial specimens from one person can minimize the effect of preanalytical sources on the reported lipid test result. A procedure using relative range can determine the number of specimens needed to assure that the total intraindividual coefficient of variation is

The combined effect of smoking and coffee drinking on LDL-HDL cholesterol

Conflicting reports on the effect of smoking and coffee drinking on lipoproteins prompted us to study the combined effect of these two associated, widely prevalent habits in 361 persons randomly sampled from the Evans County cohort. Low-density lipoprotein (LDL) cholesterol levels were significantly higher among persons who smoked cigarettes and consumed five or more cups of coffee per day than among nonsmokers who abstained from coffee. Conversely, high-density lipoprotein (HDL) cholesterol was higher in persons who did not smoke or drink coffee than in coffee-consuming smokers. However, this trend was not statistically significant. Triglycerides and very low-density lipoprotein (VLDL) cholesterol were highest among smokers who drank five or more cups of coffee per day, but these differences did not reach statistical significance. Lipoprotein cholesterol levels were adjusted for age, sex and body mass. Smoking and coffee drinking interact in affecting LDL and total cholesterol, but coffee drinking alone did not appear to affect blood lipids.

Interpreting lipid values in the laboratory

Useful laboratory interpretation depends on 3 factors: a valid sample, an accurate method and a specific interpretation. A, valid sample may be affected by a number of conditions. For example, precollection conditions are important. Among the circumstances that influence the precollection condition are the patient’s life-style, diet, exercise and medication, especially diuretics. Intercurrent illness can also alter a patient’s lipid levels; e.g., cholesterol levels drop dramaticaily in the weeks after a myocardial infarction. Several factors that influence collection conditions deserve consideration. For example, if a person is recumbent for 20 minutes before a sample is taken, there can be a 15% change in the cholesterol value. If the tourniquet is applied too tightiy for longer than 2 minutes, a change of 2 to 10% in the value can result. In addition, the anticoagulant used in the vacuum container can dramatically affect the sample. Heparin does not cause any difference between plasma or serum; however, versene causes a 3 to 5% difference. Oxalate creates an 8% difference, and citrate and fluoride can cause changes of as much as 12 and 18%, respectively. When using plasma, a full tube should always be collected. The source of the blood also affects the cholesterol level; there are differences between arterial and venous blood. With regard to laboratory conditions, the measurement will be affected by the handling, storage and shipment of the specimen. In addition, the laboratory should have stable material with which to perform its analysis.