Assays For LDL-cholesterol Research Articles

Evaluation of 13 Formulae for Calculated LDL-C Using Direct Homogenous Assay in a South Indian Population.

LDL cholesterol (LDL-C) is regarded as a significant therapeutic target and a known risk factor for atherosclerosis. It can be calculated using the results of the other lipid tests or tested directly. Despite its shortcomings, the Friedewald formula is most frequently utilized since it is simple and practical. Until now, several formulae have been proposed for calculating LDL-C; however, their accuracy has not been evaluated across different populations. We sought to evaluate the validity of calculated LDL-C by comparing the findings with values acquired by the direct homogeneous technique, utilizing 13 distinct formulae from the literature. This study was a retrospective observational study conducted for a year at SRIHER, Chennai, Tamil Nadu, India. From the total 25 043 patients who had their serum lipid profile tested, 16 314 participants had their fasting blood sugar and fasting lipid profile measured simultaneously, and they were chosen for the research. The de Cordova, Chen, Martin/Hopkins (initial), and Teerakanchana equations correlated well with the direct LDL-C assay. When the dataset was stratified according to triglycerides, the Chen and Martin/Hopkins initial equations had the better measurement of agreement compared to other equations. The Martin/Hopkins initial equation outperformed all the other equations when the whole dataset irrespective of the triglyceride population was considered. Our study suggests that the Martin/Hopkins initial equation outperformed all the other equations and can be used as an alternative to direct LDL-C measurement in a South Indian population.

Multivariate analysis by OPLS as a novel tool to identify cause of variation between assays for direct LDL measurement in frozen and fresh plasma samples

Background and Aims: Direct LDL-cholesterol (dLDL-C) assays are widely used instead of calculated LDL-C. Although theoretically more accurate, inter-assay differences still exist. This study aimed to investigate whether an OPLS multivariate model could identify the cause of discrepancy in dLDL assays in frozen and fresh plasma samples.

Membership in a diabetes-care network and adherence to clinical practice guidelines for treating type 2 diabetes among general practitioners: A four-year follow-up

ObjectivesTo assess whether private general practitioners (GPs) belonging to a diabetes-care network adhered more closely to clinical practice guidelines for diabetes care than GPs not in such a network, for all their patients with type 2 diabetes treated with medication (patients with diabetes), regardless of whether they received care through a network (that is, whether a halo effect occurred). Research design and measuresThe study, based on health insurance reimbursement databases in southeastern France, included 468 GPs in two networks and 468 non-network GPs in the same geographical area, matched one-to-one by propensity scores. We followed up their patients with diabetes (n=22,808) from 2008 through 2011, conducting multivariate time-to-event analyses (Cox models) that took the matching design into account to evaluate time from inclusion until performance of the given number of each of six recommended examinations/tests. ResultsGPs belonging to a diabetes-care network adhered more closely to clinical practice guidelines but our result were slightly pronounced. Hazard ratios (HR) were significantly higher for patients of network GPs for the implementation of 3 HbA1C assays (HRa=1.13; [95%CI=1.10–1.16]), or 1 microalbuminuria assay (1.4 [1.35–1.45]); they were lower for LDL-cholesterol assays (1.04 [1.01–1.07]) and ophthalmological checkups (1.07 [1.04–1.10]), and not significant for creatinemia or cardiac monitoring. ConclusionsNetwork GPs had better diabetes monitoring practices for all their patients with diabetes than the other GPs, especially for the most diabetes-specific tests. Further research is needed in other settings to confirm the existence of this halo effect.

Evaluation of modified homogeneous LDL cholesterol assay by selective solubilization method

Evaluation of modified homogeneous LDL cholesterol assay by selective solubilization method

Differences in reaction specificity toward lipoprotein X and abnormal LDL among 6 homogeneous assays for LDL-cholesterol

BackgroundWe investigated the reaction specificity toward cholesterol in lipoprotein X (Lp-X) and abnormal LDL among 6 homogeneous assays for low-density lipoprotein cholesterol (LDL-C) based on different measurement principles. MethodsThe homogeneous LDL-C assays used were based on the liquid selective detergent, selective solubilization, elimination, enzyme-selective protection, calixarene complex, and phosphate complex inhibition methods. The fraction with a density of 1.006–1.063kg/l was isolated from cholestatic sera, and the reactivity of cholesterol in the lipoprotein fractions by gel filtration for each homogeneous LDL-C assay was determined. ResultsThe liquid selective detergent and elimination methods showed increased cholesterol reactivity in the Lp-X fraction in a concentration-dependent manner, while the selective solubilization and phosphate complex inhibition methods were less reactive toward Lp-X cholesterol. Meanwhile, the homogeneous LDL-C assays showed decreased reactivity against cholesterol in abnormal LDL, with increased ratios of phospholipids and triglycerides against cholesterol. ConclusionThe homogeneous LDL-C assays showed differential reactivity toward Lp-X and abnormal LDL. Our findings enable accurate interpretation of the LDL-C values in these homogeneous assays, and suggest that these methods should be improved to distinguish between normal LDL and abnormal LDL or Lp-X.

フィルター法による small, dense LDLコレステロール測定法の特徴および性能

フィルター法による small, dense LDLコレステロール測定法の特徴および性能

A multicenter study on the precision and accuracy of homogeneous assays for LDL-cholesterol: Comparison with a beta-quantification method using fresh serum obtained from non-diseased and diseased subjects

BackgroundHomogeneous assays for low-density lipoprotein-cholesterol (LDL-C) have good precision and are pretreatment-free procedures. However, their accuracies have been questioned, especially in diseased subjects. In this study, we aimed to verify whether LDL-C levels determined by homogeneous assays [LDL-C (H)] agree with those determined by a beta-quantification method [LDL-C (BQ)] in fresh clinical samples. MethodsWe determined LDL-C levels in 49 non-diseased and 124 diseased subjects whose triglyceride (TG) levels were less than 11.29 mmol/L (1000 mg/dL) using 12 homogeneous assays and a BQ method simultaneously. ResultsIn total, 30.6% of non-diseased subjects and 46.0% of diseased subjects were in the postprandial state. The maximum inter- and intra-assay CVs were 1.8% and 1.5%, and 8 reagents had a CV of 1.0% or less. The mean bias ranged from −0.5% to 1.8% for non-diseased subjects and from −0.7% to 1.6% for diseased subjects. For non-diseased subjects, all but one reagent achieved the National Cholesterol Education Program (NCEP) total error requirement in more than 90% of samples. However, for diseased subjects, the number of reagents that met this requirement was low. With some reagents, LDL-C (H) was higher than LDL-C (BQ), especially in subjects with hypertriglyceridemia. While for other reagents, the difference between the two methods was not associated with hypertriglyceridemia except for type I (n = 2) and type III hyperlipidemia (n = 1). Postprandial sampling was not the main factor for discordant results. ConclusionsLDL-C (H) agrees with LDL-C (BQ) in non-diseased subjects, but exhibits positive bias for subjects with hypertriglyceridemia in diseased subjects for some reagents.

Small Dense LDL Cholesterol and Coronary Heart Disease: Results from the Framingham Offspring Study

We sought to establish reference values for a new direct assay for small dense LDL cholesterol (sdLDL-C) and to measure sdLDL-C concentrations in patients with established coronary heart disease (CHD) vs controls. Direct LDL-C and sdLDL-C were measured in samples from 3188 male and female participants of the Framingham Offspring Study, including 173 men and 74 women with CHD. Postmenopausal status and male sex were associated with higher sdLDL-C concentrations (P < 0.0001). Cholesterol-lowering medication use was more frequent (P < 0.0001) in CHD patients than in controls (46.8% vs 11.4% in men; 35.1% vs 8.8% in women). In men, mean LDL-C was lower in CHD than in controls (3.22 vs 3.51 mmol/L, P < 0.0001), whereas mean sdLDL-C concentrations were similar (0.83 vs 0.84 mmol/L, P = 0.609). In women, mean LDL-C was similar in CHD and controls (3.53 vs 3.46 mmol/L, P = 0.543), but mean sdLDL-C was higher (0.83 vs 0.68 mmol/L, P = 0.0015). The mean percentage of LDL-C as sdLDL-C was higher in both men and women with CHD than controls (P < 0.01). Increased LDL-C and sdLDL-C were found in 10.4% and 22.0% of men and in 24.3% and 27.8% of women with CHD, respectively. Despite 4-fold greater cholesterol-lowering therapy use, CHD patients had mean LDL-C concentrations above the LDL-C goal of <2.6 mmol/L (<100 mg/dL). Although women with CHD had higher sdLDL-C concentrations than controls, this difference was not seen in men. These findings may explain some of the high residual risk of future CHD events in CHD patients.

Differential reactivities of four homogeneous assays for LDL-cholesterol in serum to intermediate-density lipoproteins and small dense LDL: Comparisons with the Friedewald equation

Background In routine clinical laboratory testing and numerous epidemiological studies, LDL-cholesterol (LDL-C) has been estimated commonly using the Friedewald equation. We investigated the relationship between the Friedewald equation and 4 homogeneous assays for LDL-C. Methods LDL-C was determined by 4 homogeneous assays [liquid selective detergent method: LDL-C (L), selective solubilization method: LDL-C (S), elimination method: LDL-C (E), and enzyme selective protecting method: LDL-C (P)]. Samples with discrepancies between the Friedewald equation and the 4 homogeneous assays for LDL-C were subjected to polyacrylamide gel electrophoresis and the β-quantification method. Results The correlations between the Friedewald equation and the 4 homogeneous LDL-C assays were as follows: LDL-C (L) ( r = 0.962), LDL-C (S) ( r = 0.986), LDL-C (E) ( r = 0.946) and LDL-C (P) ( r = 0.963). Discrepancies were observed in sera from type III hyperlipoproteinemia patients and in sera containing large amounts of midband and small dense LDL on polyacrylamide gel electrophoresis. LDL-C (S) was most strongly correlated with the β-quantification method even in sera from patients with type III hyperlipoproteinemia. Conclusions Of the 4 homogeneous assays for LDL-C, LDL-C (S) exhibited the closest correlation with the Friedewald equation and the β-quantification method, thus reflecting the current clinical databases for coronary heart disease.

Comparison of LDL Cholesterol Concentrations by Friedewald Calculation and Direct Measurement in Relation to Cardiovascular Events in 27 331 Women

National Cholesterol Education Program (NCEP) guidelines recommend development of direct assays for LDL cholesterol (LDL-C) measurement, but it is unclear how these assays compare with Friedewald calculation in predicting cardiovascular disease (CVD). In a study of 27 331 healthy women with triglycerides <or=4.52 mmol/L (<or=400 mg/dL), baseline fasting Friedewald LDL-C was compared with fasting and nonfasting direct homogenous measurement for incident CVD during an 11-year period. Fasting LDL-C measurements obtained by the 2 methods were highly correlated (r = 0.976, P < 0.001). Compared with fasting Friedewald LDL-C, mean fasting direct LDL-C was 0.15 mmol/L (5.6 mg/dL) lower and nonfasting direct LDL-C 0.30 mmol/L (11.5 mg/dL) lower, both P < 0.0001. The adjusted hazard ratio per 1-SD increment was 1.23 [95% CI 1.15-1.32; 1-SD 0.88 mmol/L (34.1 mg/dL)] for fasting direct LDL-C and 1.22 [95% CI 1.14-1.30; 1-SD 0.90 mmol/L (34.9 mg/dL)] for fasting Friedewald. Nonfasting LDL-C was not associated with CVD by either method. Fasting LDL-C measurements fell into the same NCEP risk category with either method for 79.3% of participants, whereas they differed by 1 NCEP category for 20.7% of participants, with most classified into a lower-risk category by direct LDL-C. The association of LDL-C with CVD by the 2 methods was nearly identical in fasting samples. However, the lower direct LDL-C concentrations may misclassify many individuals into a lower NCEP category. Moreover, the lack of association of nonfasting direct LDL-C with CVD raises questions regarding the clinical utility of a direct assay for LDL-C in nonfasting blood samples.

Rapid and Simple Profiling of Lipoproteins by Polyacrylamide-Gel Disc Electrophoresis to Determine the Heterogeneity of Low-Density Lipoproteins (LDLs) Including Small, Dense LDL

This study aimed to explore the potential of polyacrylamide-gel disc electrophoresis (PAGE) for lipoprotein profiling in clinical practice. Blood samples were collected from 146 patients with type 2 diabetes mellitus and lipid parameters were assayed by PAGE, including small, dense low-density lipoprotein (LDL) (n = 41), and triglyceride-rich lipoprotein remnant cholesterol (n = 37). We also used a commercial kit to measure small, dense LDL (n = 41). By PAGE, we obtained the percentage of the area under the curve (AUC %) of each peaks and calculated respective AUC% x total cholesterol (AUC%xTC) values. The calculated values of LDL-AUC%xTC, small LDL-AUC%xTC, and HDL-AUC%xTC values were correlated well with values from homogeneous assay for LDL-cholesterol, small, dense LDL-cholesterol, and HDL-cholesterol assays (r = 0.94, 0.81, and 0.89, respectively). PAGE combined with measurement of total cholesterol and triglycerides provides a rapid evaluation of anti- or pro-atherogenic lipoproteins and a simple profiling system for both the "quantity" and "quality" of lipoproteins, allowing a better assessment of the risk of coronary artery diseases. This article discusses several methods for simple and rapid lipid profiling and outlines some recent patents relevant to the methods.

Fasting versus Nonfasting Triglycerides and the Prediction of Cardiovascular Risk: Do We Need to Revisit the Oral Triglyceride Tolerance Test?

Historically, triglycerides have been measured in the fasting state for 2 reasons. First, because of the marked increase in triglycerides after fat ingestion, the variability in triglyceride measurements is much smaller in the fasting state. Second, before the availability of direct assays for LDL cholesterol (LDL-C),1 estimation of LDL-C was performed in clinical practice almost exclusively by use of the Friedewald equation, which requires that both the HDL-C concentration and the fasting triglyceride concentration divided by 5 be subtracted from the total cholesterol concentration. The recommendations to measure triglycerides in the fasting state did not, however, derive from a consistent set of prospective cohort studies showing that fasting concentrations were superior to nonfasting concentrations for the detection of cardiovascular risk. Instead, following screening guidelines, most epidemiologic investigations simply relied on fasting triglycerides. Taken as a whole, such studies indicate that fasting triglycerides are a univariate predictor of vascular disease. Controversy exists, however, regarding the clinical usefulness of fasting triglycerides as an independent predictor of risk, because adjustment for other covariates—in particular HDL-C—markedly decreases both the magnitude and significance of observed epidemiologic effects (1). The extent to which investigators have sought to avoid nonfasting triglycerides as a method for risk detection is evident in a recent metaanalysis that limited evaluation only to those epidemiologic studies that measured fasting triglycerides, specifically “to exclude the possibility of postprandial effects” (2). Is it possible, then, that recommendations to measure triglycerides in the fasting state have systematically underestimated the impact of hypertriglyceridemia in clinical practice? Atherosclerosis has long been hypothesized to be a disorder influenced by postprandial effects. As early as 1950, J. R. Moreton, writing in the Journal of Laboratory and Clinical Medicine , suggested a linkage between chylomicronemia, fat tolerance, and atherosclerosis (3). A major source of circulating triglycerides is dietary …

Comparative study between anion-exchange HPLC and homogeneous assay methods in regard to the accuracy of high- and low-density lipoprotein cholesterol measurement

Objectives: A convenient method based on anion-exchange HPLC was recently developed to determine cholesterol levels of lipoproteins (HDL, LDL, IDL, VLDL, and chylomicron). The present study was performed to compare this HPLC method to homogenous assay in regard to measurement accuracy of HDL and LDL cholesterol. Design and methods: Serum samples ( n = 105), including three samples from cholestasis patients, were measured by homogenous assay with Cholestest-LDL and CholestestN-HDL (Daiichi Chemicals, Tokyo) and by HPLC as reported previously ( J Lipid Res 2003; 44: 1404–12). Results: The homogenous assay for HDL cholesterol correlated strongly with the HPLC method for HDL cholesterol ( r = 0.976). Two samples from cholestasis patients could not be measured by homogenous assay but were measured by HPLC. The homogenous assay for LDL cholesterol correlated modestly with the HPLC method for LDL cholesterol ( r = 0.823). Three outlier samples, from cholestasis patients with serum cholesterol levels > 17 mmol/L, were observed in this correlation analysis. Homogenous assay data showed that these LDL cholesterol levels were 15.2–34.7 mmol/L. However, HPLC data showed that these LDL cholesterol levels were 3.6–8.2 mmol/L, and that the major lipoprotein fractions were VLDL and IDL. The difference in LDL cholesterol levels (homogenous assay data minus HPLC data) was positively correlated with VLDL cholesterol levels. Conclusions: When measuring samples from cholestasis patients, homogenous assay may give inaccurate results. In contrast, the HPLC method is likely to be capable of accurately measuring HDL and LDL cholesterol levels without the involving VLDL.

Improved Specificity of a New Homogeneous Assay for LDL-Cholesterol in Serum with Abnormal Lipoproteins

Although a homogeneous assay for serum LDL-cholesterol (LDL-C) has become a routine clinical procedure, problems remain in assay performance characteristics. We examined the performance of a recently developed automated homogeneous assay (New-Daiichi assay) for serum LDL-C and compared the results with those obtained by the current homogeneous method (Denka-Seiken assay) or by ultracentrifugation as a control. The New-Daiichi assay showed satisfactory basic performance characteristics such as reproducibility, linearity, and stability. There was no interference in the assay by various substances examined. The LDL-C values obtained with this method correlated well with those obtained by ultracentrifugation. In samples from patients with obstructive jaundice, both methods detected cholesterol from abnormal lipoproteins (such as lipoprotein-X and -Y), but the New-Daiichi assay was less reactive and more specific for LDL-C. The new method has improved performance for the accurate measurement of LDL-C in clinical practice.

The effects of exercise training on abdominal visceral fat, body composition, and indicators of the metabolic syndrome in postmenopausal women with and without estrogen replacement therapy: The HERITAGE family study

The purpose of this research was to investigate the effects of apriori estrogen replacement therapy (ERT) and endurance exercise training in postmenopausal women on abdominal visceral fat (AFV) and other selected variables related to body composition and the metabolic syndrome (MS). Forty-eight healthy and previously sedentary postmenopausal women (mean age, 54.3 years) who were enrolled in the HERITAGE Family Study (HFS) served as subjects. Of these 48 women, 18 were currently taking ERT and the remaining 30 were taking no supplemental estrogen (NHRT). Computed tomography (CT) scans were used to assess AVF as well as total abdominal fat (TAF) and abdominal subcutaneous fat (ASF). Body mass index (BMI) and waist-to-hip ratios (WHR) were calculated while body fat percentage (%FAT) and total fat mass (FATM) was assessed using underwater weighing. Blood assays for HDL-cholesterol (HDL-C), LDL-cholesterol (LDL-C), and triglycerides (TG) were conducted at a Centers for Disease Control (CDC) certified laboratory, while blood pressure measurements were assessed using an automated system. All measurements were obtained in duplicate before and after a regimen of endurance exercise training. Analysis of variance (ANOVA) showed AVF to be an average of 31.6 cm 2 less in the women receiving ERT, but lost statistical significance when AVF was adjusted for FATM. Mean values for TAF, ASF, and waist girth were also less in the women receiving ERT, but only waist girth achieved statistical significance. No differences were found in BMI or %FAT, but mean WHR was 5% smaller in the ERT group. Baseline values for HDL-C was higher and LDL-C lower in the ERT group. Prevalence of the MS tended to be greater in the NHRT group, but did not achieve statistical significance. There were no differences in training responses in any of the body composition variables between groups, however, in the ERT group LDL-C decreased with training while TG increased. It was concluded that postmenopausal women taking ERT tended to have lower values of AVF and other indicators of body composition, a more favorable lipid profile, and a slightly reduced risk of the MS when compared with women not taking supplemental hormones. Also exercise training did not improve the overall MS status of either group, as LDL-C status improved in the ERT group while TG decreased in the NHRT group.

Differential Reactivity of Two Homogeneous LDL-Cholesterol Methods to LDL and VLDL Subfractions, as Demonstrated by Ultracentrifugation and HPLC

The analytical and clinical performance of homogeneous LDL-cholesterol assays has been reported, but their reactions with subfractions of LDL and VLDL have not been described in detail. We evaluated reaction selectivity of two homogeneous LDL-cholesterol assays, LDLk (Kyowa Medex) and LDLd (Daiichi Pure Chemical), with ultracentrifugally isolated VLDL and LDL subfractions to identify the lipoprotein particles from which the cholesterol recognized by these assays originates. The LDLd (y) and LDLk (x) methods correlated highly for whole serum samples: y = 0.986x - 39.5 mg/L (r = 0.966; n = 34). In isolated VLDL, the LDLk and the LDLd methods recovered 17.3% and 23.8% of cholesterol, respectively; but correlation analysis revealed differential reactivity to small and large VLDL particles. For the isolated LDL subfraction of density 1.019-1.040 kg/L, the LDLd method had significantly higher reactivity (95.6-98.7%) than the LDLk (88.4-92.0%). Both methods, however, demonstrated poor recovery (approximately 50%) for the 1.050-1.063 kg/L fraction, indicating incomplete reactivity with small, dense LDL. Reactivity with lipoprotein(a) was better (71.2-90.8%) for both methods than with small LDL. For intermediate-density lipoprotein (IDL), there was no significant difference in recovery between the two methods (71.7% for LDLk and 68.9% for LDLd), but the LDLk method appeared to be more sensitive to IDL particle size. The two homogeneous assays for LDL-cholesterol demonstrate only partial reactivity to small, dense LDL and nonspecific reactions to VLDL particles. Modification will be required in the homogeneous methods to obtain LDL-cholesterol values equivalent to those obtained by ultracentrifugation.

LDL-cholesterol and HDL-cholesterol concentrations decrease during the day.

Homogenous assays for LDL-cholesterol (LDL-C) and HDL-cholesterol (HDL-C) are highly accurate, with little interference from triglyceride. Using these methods, we measured postprandial LDL-C and HDL-C. Earlier studies suggested a postprandial decrease in LDL-C. To elucidate whether LDL-C and HDL-C decrease significantly during the day, we determined daily profiles of LDL-C and HDL-C using homogeneous assays in subjects with normal coronary arteries (N; n=10), and subjects with coronary artery disease (CAD; n=23). In both groups, LDL-C and HDL-C were significantly lower from after breakfast until midnight than they were before breakfast. The next morning, they returned to baseline levels. The mean reduction in LDL-C was 0.09-0.13 mmol/L in N and 0.05-0.20 mmol/L in CAD, while that in HDL-C was 0.02-0.06 mmol/L in N and 0.00-0.05 mmol/L in CAD. LDL-C and HDL-C decrease significantly over the course of the day.

Evaluation of a Homogeneous Direct LDL-Cholesterol Assay in Diabetic Patients: Effect of Glycemic Control

Increased serum LDL-cholesterol (LDL-C) is associated with increased risk for ischemic heart disease, and lowering of LDL-C has been shown to decrease mortality in patients with known coronary heart disease (1)(2)(3). Persons with diabetes have a greatly increased risk for atherosclerosis and its complications. Many of these patients have increased plasma cholesterol (including LDL-C) and triglycerides (TGs). Additionally, glycation and oxidation of circulating LDL particles may further increase the risk for atherosclerotic disease in patients with diabetes (4)(5). Currently used methods for LDL-C include calculations [based on total cholesterol (TC), HDL-cholesterol (HDL-C), and TG concentrations], ultracentrifugation, and most recently, direct LDL-C assays. Calculation methods, such at the Friedewald formula (6), are well known to have a prominent negative bias in patients with TG concentrations >4.5 mmol/L (400 mg/dL) (6)(7). In addition, because TGs are measured, fasting blood samples are preferred. This can present a problem for certain patient populations, including many people with diabetes. Ultracentrifugation methods are time-consuming and expensive and generally are performed only in reference laboratories. Direct LDL-C assays have been developed recently and have been shown to provide accurate and precise measurements of LDL-C (8)(9)(10)(11)(12). They overcome the TG and fasting limitations of calculation methods, are readily adapted to clinical laboratories, are less expensive than ultracentrifugation methods, and provide greatly improved turnaround time. Direct LDL-C assays make use of either an immunoseparation step or specific detergents to separate LDL particles from other lipoproteins, followed by measurement of cholesterol by conventional enzymatic reactions. The N-geneousTM LDL-C assay is a solute-based homogeneous assay that agrees well with ultracentrifugation (11). The purpose of the present study was to evaluate the effect of glycemic control (as gauged by hemoglobin A1c) on the …

Evaluation of Two Different Homogeneous Assays for LDL-Cholesterol in Lipoprotein-X-positive Serum

The purpose of this study was to evaluate the performance of two homogeneous assays for LDL-cholesterol (LDL-C), a polyethylene/cyclodextrin (PC) assay and a detergent (D) assay, which are based on different principles, in cholestatic serum. We compared serum LDL-C concentrations determined by the two assays for healthy normolipidemic subjects (n = 42) and cholestatic patients (n = 51). LDL-C concentrations obtained with the homogeneous assays were also compared with those obtained by HPLC for patients' sera. In the interference study, conjugated bile acids were added to normal serum, and their effects on the two assays were examined. The effects of lipoprotein-X (LP-X), intermediate-density lipoprotein (IDL), and apolipoprotein (apo) E-rich HDL on the LDL-C assays were also investigated by adding these lipoproteins to normal serum. The LDL-C concentrations obtained with the D assay were higher than those obtained with the PC assay in the serum with high LP-X. The bias for LDL-C vs LP-X in cholestatic serum correlated with LP-X concentration (r = 0.582; P: <0.0001; n = 51). In the interference study, no effect of bile acids on the LDL-C assays was observed. However, the D assay measured 51.0% of the cholesterol in LP-X, whereas no reactivity was observed for LP-X in the PC assay. In addition, the D assay and the PC assay measured IDL-cholesterol at 31.2% and 52.4%, respectively, and measured apo E-rich HDL-C at 7.6% and 17.8%, respectively. Although both homogeneous LDL-C assays are suitable for most cases, the present study showed that each homogeneous assay has a different limitation for cholestatic serum with gross alterations in lipoproteins.

Analytical and Clinical Evaluation of Two Homogeneous Assays for LDL-Cholesterol in Hyperlipidemic Patients

LDL-cholesterol (LDL-C) concentrations are the primary basis for treatment guidelines established for hyperlipidemic patients. LDL-C concentrations are commonly monitored by means of the Friedewald formula, which provides a relative estimation of LDL-C concentration when the triglyceride concentration is <2000 mg/L and there are no abnormal lipids. The Friedewald formula has several limitations and may not meet the current total error requirement of <12% in LDL-C measurements. We evaluated the analytical and clinical performance of two direct methods (Roche and Wako) by analyzing 313 fresh serum samples obtained from dyslipidemic patients in a lipid clinic and comparing them with modified beta-quantification. Both homogeneous assays displayed excellent precision (CV <2%). The Roche method showed a mean total error of 7.72%, and the Wako method showed a mean total error of 4.46% over a wide range of LDL-C concentrations. The Roche method correlated highly with the modified beta-quantification assay (r = 0.929; y = 1.052x - 168 mg/L; n = 166) and showed a bias of -4. 5% as a result of the assigned standard value. The Wako method also correlated highly with beta-quantification (r = 0.966; y = 0.9125x + 104.8 mg/L; n = 145) without significant bias. The Roche method correctly classified 97% of patients with triglycerides <2000 mg/L, 75% of patients with type IIb hyperlipemia (HPL), and 84% of patients with type IV HPL based on the cutpoints of 1300 and 1600 mg/L, compared with 98%, 78.4%, and 89%, respectively, for the Wako method. In dysbetalipoproteinemic patients, both methods have a 30% mean positive bias compared with beta-quantification. Both direct methods can be a useful alternative when ultracentrifugation is not available for the diagnosis and control of lipid-lowering medication for patients with mixed HPL, but not for patients with type III hyperlipidemia.