Biomedical subjects

G R Warnick

Publications and source records attributed to G R Warnick.

At least 19 recordsLinked to original sources

PubMed1995

Accurate direct determination of low-density lipoprotein cholesterol using an immunoseparation reagent and enzymatic cholesterol assay.

Clinical laboratories currently estimate low-density lipoprotein cholesterol using the Friedewald formula, which requires fasting specimens and is subject to error with increasing triglyceride levels. We describe a rapid method for isolating low-density lipoproteins using the Direct LDL Immunoseparation Reagent for subsequent measurement of cholesterol by conventional assay. This method meets current guidelines for precision with within-run and run-to-run coefficients of variation of less than 3%. Results are in good agreement with the beta quantification reference method (Direct LDL-C = 1.03 [beta quantification] -0.06 mmol/L, [2.4 mg/dL] r = 0.980), there is minimal bias associated with increasing triglycerides or high-density lipoprotein cholesterol, and patient fasting is not required for accurate analysis. The Direct LDL Immunoseparation Reagent overcomes drawbacks of the Friedewald formula and appears to be suitable for accurate quantitation of low-density lipoprotein cholesterol in the routine laboratory.

Bias↗

PubMed1994

Modification of the dextran-Mg2+ high-density lipoprotein cholesterol precipitation method for use with previously frozen plasma.

Although dextran-Mg2+ precipitation produces accurate and precise results for high-density lipoprotein (HDL) cholesterol in fresh plasma and serum, precipitation of frozen specimens with triglycerides > 2.26 mmol/L (> 200 mg/dL) is difficult. We developed a modification that dilutes thawed samples by 35% and increases dextran-Mg2+ reagent to 15% of sample volume. Standard precipitations were performed on 62 fresh EDTA-treated plasma specimens; supernatant solutions were analyzed fresh and after freezing. Standard and modified methods were also performed on thawed, paired plasmas. In specimens with triglycerides < or = 2.26 mmol/L, HDL cholesterol results for all methods were similar. For triglycerides > 2.26 mmol/L, however, bias and precision were significantly affected by freezing, and 38.5% of samples with standard precipitation required additional procedures to produce clear supernatant solutions. HDL cholesterol concentrations for thawed samples with standard precipitation were significantly greater than for fresh samples (P < 0.02), but those for the modified method were not different from fresh samples, and only one specimen required additional steps to produce a clear supernate.

Chemical Precipitation↗

PubMed1992

Measurement of low-density-lipoprotein cholesterol in serum: a status report.

Current recommendations of the Adult Treatment Panel and the Children and Adolescents Treatment Panel of the National Cholesterol Education Program make the concentration of low-density lipoproteins cholesterol (LDL-C) in serum the basis for the classification and treatment of hypercholesterolemia. Numerous methodologies for the determination of serum LDL-C concentrations, in research and clinical laboratories, have been described. Here, we review the principles, performance, and limitations of major current methodologies for determining LDL-C concentrations. These methods include sequential and density-gradient ultracentrifugation, chromatographic and electrophoretic techniques, and precipitation methods. In addition, the advantages and disadvantages of estimating LDL-C concentration by the Friedewald equation, the most commonly used approach in clinical laboratories, are addressed.

Chemical Precipitation↗

PubMed1990

Laboratory measurement of lipid and lipoprotein risk factors.

Accuracy in measurement of serum cholesterol and the other lipid risk factors is essential for reliable patient classification within the context of newly implemented national coronary heart disease intervention programs utilizing uniform cutpoints. This requires agreement or traceability of laboratory methods to national reference systems, which provided the accuracy base for the population studies from which the cutpoints are derived. Adhering to accepted guidelines for patient preparation, blood collection and processing will minimize preanalytical variability. Standardization of the lipid/lipoprotein assays is the next essential step. The assay technology for cholesterol measurement is reasonably mature, although still not perfected; recent activities have focused primarily on achieving traceability of field methods through improving access to the accuracy base, the National Reference System for Cholesterol and developing better (commutable) reference materials. A major hindrance to standardization has been matrix interactions; alterations in reference materials from their preparation which change the measurement characteristics, necessitating the use of fresh specimens in accuracy studies. Considering the importance of LDL cholesterol which is the primary decision parameter in the new clinical guidelines; methodology for routine laboratory quantification is substantially lacking, the usual routine approach still involving estimation. Efforts to develop a reference system for LDL are just beginning. Field methods for HDL cholesterol are reasonably reliable but with some inter-method differences. Agreement on and access to a Reference Method is needed. Accuracy in triglyceride measurement is less important compared to the other risk factors. Convenient methods allowing correction for the free glycerol blank and ready access to a Reference Method are needed.

Chemistry, Clinical↗

PubMed1990

Estimating low-density lipoprotein cholesterol by the Friedewald equation is adequate for classifying patients on the basis of nationally recommended cutpoints.

We compared low-density lipoprotein cholesterol (LDL) values obtained by the Friedewald formula--i.e., total cholesterol minus high-density lipoprotein (HDL) cholesterol minus very-low-density lipoprotein (VLDL) cholesterol (estimated as triglyceride divided by 5)--with those obtained by lipoprotein fractionation, using 4736 specimens. When triglycerides were less than 2.0 g/L, greater than 90% of estimated LDL cholesterol values were acceptable, within +/- 10% of measured values. At triglyceride concentrations of 2.0-4.0 g/L and 4.0-6.0 g/L, only 72% and 39%, respectively, of the estimates were acceptable. LDL values derived from an alternative formula, estimating VLDL as triglycerides divided by 6, were even less accurate. Nevertheless, the use of estimated LDL for risk classification based on the National Cholesterol Education Program Adult Treatment Panel cutpoints of 1.30 and 1.60 g/L was considered acceptable. At triglyceride concentrations less than or equal to 5.0 g/L, 88% of classifications based on estimated LDL (using triglycerides divided by 5) were concordant with those by measured LDL. Eleven percent of classifications were shifted across one cutpoint, evenly distributed between high and low. Fewer than 1% of classifications, all with Type III hyperlipoproteinemia, were misclassified two cutpoints high. Refinements in the estimation model did not substantially improve LDL estimation or concordance of risk classification.

Adult↗

PubMed1989

Cancer risk in relation to serum copper levels.

A nested, matched case-control study was conducted to assess the relationship between serum levels of copper and the subsequent risk of cancer. One hundred thirty-three cases of cancer were identified during 1974-1984 among 5000 members of a northwest Washington State employee cohort from whom serum specimens had been previously obtained and stored. Two hundred forty-one controls were selected at random from the cohort and were matched to the cases on the basis of age, sex, race, and date of blood draw. Serum copper levels were measured by atomic absorption spectrometry. Risk of a subsequent diagnosis of cancer was positively associated with serum copper levels, but only among those cases diagnosed within 4 years of the time the serum specimens were collected. Among cases diagnosed more than 4 years after specimen collection, there was no consistent association between serum copper levels and risk. Adjustment for age, sex, race, occupational status, cigarette smoking, family history of cancer, alcohol consumption, and, among females, use of exogenous hormones had no appreciable effect on these relationships. The findings suggest that the presence of cancer may increase serum copper levels several years prior to its diagnosis. They are less supportive of the hypothesis that serum copper levels affect cancer risk.

Adult↗

PubMed1989

Lipoprotein, apolipoprotein, and lipolytic enzyme changes following estrogen administration in postmenopausal women.

To test whether estrogen can modulate the cholesterolemic response to an Occidental diet, six healthy postmenopausal women were studied for 84 days while ingesting a solid food diet of constant composition high in cholesterol content (995 mg/d). In the middle of the study, estrogen (17 alpha-ethinyl estradiol, 1 microgram/kg per day) was administered orally. Ingestion of the diet for the initial 28 days did not alter lipoprotein lipid or apolipoprotein (apo) levels. However, with just 4 days of estrogen use there were significant decreases in apoE (-36%), low density lipoprotein cholesterol (-26%), and postheparin plasma hepatic triglyceride lipase activity (HTGL) (-61%), and an increase in high density lipoprotein (HDL) triglyceride (72%). These changes persisted throughout the estrogen use. The percent change in HTGL with 4 days of estrogen correlated inversely with the percent change in HDL triglyceride (rs = -0.94). After 28 days of estrogen there were also significant increases in HDL cholesterol (21%), HDL2 cholesterol (42%), apoA-I (37%), and apoA-II (9%), and a decrease in apoB (-11%). The level of apoE at this juncture correlated inversely with the level of HDL cholesterol (rs = -0.90), and the levels of HTGL and apoA-I correlated with HDL2 cholesterol (rs = -0.89 and rs = 0.89, respectively). Thus, HTGL may play a role in both the early estrogen-related changes in HDL triglyceride and apoE and the late estrogen-related changes in HDL cholesterol, apoA-I, and apoA-II.

Aged↗

PubMed1989

Measurement of cholesterol, triglycerides, and HDL using compact analysis systems.

The compact analyzers facilitate rapid measurement of cholesterol and other lipid parameters outside the conventional laboratory setting. The current generation of instruments has very different features, operating parameters, and performance characteristics, and they must be selected in accordance with the intended application. All three of the common screening instruments, the DT-60, the Reflotron, and the VISION, have demonstrated the capability to meet current performance guidelines, provided they are operated correctly. Attention to quality assurance will, nevertheless, be essential in achieving reliable results. Further refinements in the instruments, reagents, and applications will improve their utility in screening programs.

Cholesterol↗

PubMed1989

A rapid micro-scale procedure for determination of the total lipid profile.

We describe a one-day micro-scale procedure for determining the total lipid profile. Only 0.55 mL of plasma is needed for complete quantification of total cholesterol (TC), triglyceride (TG), and all lipoproteins. After precipitation with dextran sulfate and magnesium, the high-density lipoprotein (HDL) fraction was separated by centrifugation in an Eppendorf microcentrifuge. Very-low-density lipoprotein (VLDL) was separated from low-density lipoprotein (LDL) plus HDL in a Beckman TL 100 ultracentrifuge. TC, TG, and cholesterol in different lipoprotein fractions were measured enzymatically in a Baker "Encore II" automated analyzer. CVs, both within-day and day-to-day, were less than 3% for TG and TC, and less than 5% for HDL-C determinations. CVs for LDL-C and VLDL-C were less than 7.5% and 15%, respectively. Results by our micromethods (n = 66) agreed well with those by the conventional methods used at the Northwest Lipid Research Center, which are standardized against the Reference Methods of the Centers for Disease Control. Coefficients of correlation between the two methods were 0.98 for TC, 1.0 for TG, 0.98 for HDL-C, 0.94 for LDL-C, and 0.96 for VLDL-C. Results of electrophoresis on agarose gel and radioactivity-recovery studies indicate that our micro-centrifugation and slicing procedures result in clean separation of VLDL from other lipoproteins.

Autoanalysis↗

PubMed1989

Accuracy and precision of analyses for total cholesterol as measured with the Reflotron cholesterol method.

We compared plasma cholesterol measurements made with the Boehringer Mannheim Reflotron reflectance photometric analyzer in 1298 capillary blood samples with measurements made in venous blood samples collected at the same time and analyzed in four standardized Lipid Research Clinics laboratories. The Reflotron measurements averaged 0.8% to 7.8% lower than the laboratory values. Correlations (r) between the two sets of measurements ranged from 0.92 to 0.96. In some samples, however, the Reflotron values differed from the laboratory values by greater than or equal to 12%; the cholesterol concentrations in these samples tended to be higher than in those for which better agreement was observed. The smaller negative biases were observed when test strips were used that were calibrated with reference to the Centers for Disease Control Reference Method for cholesterol. The agreement between sequential Reflotron values averaged less than or equal to 4.3%. There was an average difference of less than or equal to 1.0% between Reflotron measurements made in each of two sequential capillary blood samples taken from a single finger puncture.

Cholesterol↗

PubMed1989

Standardization of a commercial (Boehringer Mannheim diagnostics) enzymic method for cholesterol.

The Laboratory Standardization Panel of the National Cholesterol Education Program recommends that cholesterol method accuracy ideally be within 3% of the true value determined by the Abell-Kendall Reference Method, a component of the National Reference System for Cholesterol. As one of the Abell-Kendall network laboratories established to facilitate cholesterol standardization, the approach we recommend for determining accuracy involves a comparison analysis on patients' specimens by the method in question and by the Abell-Kendall method. Use of fresh specimens precludes matrix interactions that may influence enzymic measurement. Using this approach, we assessed an enzymic method for cholesterol with two instruments (Boehringer Mannheim/Hitachi 717 and 737), with BMD reagent, controls, and calibrator. Fresh and frozen sera were analyzed with both instruments over three days. The Abell-Kendall method was used at the Northwest Lipid Research Center on frozen aliquots of the same sera. Both instruments demonstrated good agreement with the Reference Method, as determined by linear regression; overall bias averaged less than -2% for the Hitachi 717 and -1% for the Hitachi 737 at 2000 mg/L--i.e., within the accuracy recommendation. We observed a difference in bias for fresh and frozen specimens; with the Hitachi 717, fresh specimens exhibited -3% bias at 2000 mg/L, but there was virtually no bias of determinations of frozen specimens.

Autoanalysis↗

PubMed1988

Interlaboratory proficiency survey of cholesterol and high-density lipoprotein cholesterol measurement.

We conducted a proficiency survey of cholesterol and high-density lipoprotein (HDL) cholesterol analysis in local clinical laboratories to determine whether increased national emphasis on cholesterol measurement had resulted in changes in performance from previous surveys. Sets of frozen aliquots of plasma and HDL supernate pools were sent to nine laboratories for analysis; results were compared with Northwest Lipid Research Center values, and relationships were determined by linear regression. Of all the cholesterol measurements, 81% were considered acceptable (i.e., within 9% of the NWLRC value), and 61% of the HDL cholesterol measurements were considered acceptable (within 50 mg/L of NWLRC values). These data represented no improvement over previous surveys. Workload had increased significantly: 79% for cholesterol and 284% for HDL cholesterol. On a bias plot, six of the laboratories demonstrated inaccuracy greater than the +/- 3% recommendation within the critical range of 2000-2400 mg/L for total cholesterol. For HDL cholesterol, two laboratories demonstrated bias greater than 10% at the critical point of 350 mg/L, with three additional laboratories displaying strong bias outside the decision point. The survey results indicate that apparently further improvements must be made for laboratories to achieve acceptable performance in cholesterol analysis.

Cholesterol↗

PubMed1987

Effect of fenofibrate treatment on plasma lipoprotein lipids, high-density lipoprotein cholesterol subfractions, and apolipoproteins B, AI, AII, and E.

In this segment of a multicenter study, 36 hypercholesterolemic patients were randomly assigned to fenofibrate or placebo treatment to assess effects on plasma concentrations of lipoprotein cholesterol and triglyceride, high-density lipoprotein-cholesterol subfractions, and apolipoproteins E, B, Al, and All. All of these factors are of known or potential value in determining the patient's risk of arteriosclerosis. Observations were made during initial screening and placebo phases, a 24-week, double-blind treatment phase, and a subsequent 24-week, open-label fenofibrate phase. There were three possible expressions of fenofibrate efficacy. Changes in lipoprotein cholesterol and total triglyceride concentrations observed in these patients were very similar to those seen with the larger multicenter cohort: total triglyceride levels decreased 38 to 46 percent, low-density lipoprotein cholesterol levels decreased 13 to 20 percent, and high-density lipoprotein cholesterol levels increased 4 to 13 percent. Triglyceride concentrations were significantly reduced (p less than 0.01) in very low-density lipoprotein (50 to 56 percent, similar to those of total triglyceride and very low-density lipoprotein cholesterol), and in low-density lipoprotein cholesterol levels (17 to 21 percent). A slight but statistically insignificant decrease in high-density lipoprotein triglyceride was observed (9 to 15 percent). High-density lipoprotein2 cholesterol levels did not change significantly, whereas high-density lipoprotein3 cholesterol levels increased 8 to 16 percent, accounting for all of the increase in high-density lipoprotein cholesterol. Apoprotein All levels increased significantly (13 to 20 percent) whereas those of apolipoprotein Al did not, consistent with an increase in high-density lipoprotein3 levels, where apolipoprotein All is more abundant relative to apolipoprotein Al than in high-density lipoprotein2. Apolipoprotein B levels decreased 20 to 26 percent and those of apolipoprotein E went from 29 to 34 percent, relative to the 16 to 20 percent decreases in very low-density lipoprotein and low-density lipoprotein triglyceride and cholesterol levels. Five patients with combined elevations of triglyceride and low-density lipoprotein cholesterol treated with fenofibrate, had reductions primarily in triglyceride, total apolipoprotein E (50 percent reduction), and apolipoprotein B (18 percent) levels. High-density lipoprotein3 cholesterol levels increased 19 percent and high-density lipoprotein2 cholesterol levels were unchanged. Low-density lipoprotein cholesterol levels declined slightly in four patients and a slight rise was observed in a fifth patient.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1987

Studies of lipoproteins and fatty acids in maternal and cord blood of two racial groups in Trinidad.

The high mortality rate from coronary heart disease (CHD) among Indians compared to Negroes in Trinidad led us to test plasma lipid profiles to see whether dietary or genetic factors might be involved. There were no interracial differences in the composition of plasma cholesterol ester fatty acids of the tested women and neonates. This finding suggests that dietary fat does not account for the interracial difference in CHD, nor does the cause appear to be due to genetic differences in lipid profiles, as there was no significant difference between values for plasma triglycerides, total cholesterol, high density lipoprotein (HDL) cholesterol, apo-I, apo-II, apo B or cholesterol ester fatty acids in the cord blood of each racial group. Blood samples were collected from 69 nonpregnant and 71 postpartum, fasted Negro and Indian women. Also taken were 71 umbilical cord blood samples. The mean triglyceride level was significantly lower in the Negro nonpregnant and postpartum women than in the Indians. HDL cholesterol and apo-I values were lower in the Indian women. There were no significant differences in the total cholesterol and apo B measurements. The triglyceride values for postpartum women were higher than those of the nonpregnant Negroes and Indians (75% and 47%, respectively), whereas the total cholesterol and HDL cholesterol, apo A-I and apo A-II ranged from 9% to 29% higher in the postpartum women. Apo B was about 40% higher postpartum in both ethnic groups. The high CHD rate of Indians in Trinidad cannot be explained by dietary factors, plasma total cholesterol or fatty acid composition.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1987