Effects of sample matrix in the measurement of antithrombin by LC-MS: A role for immunocapture

Introduction

The sample matrix composition, which is greatly affected by the type of blood collection tube used during phlebotomy, is of major importance in laboratory testing as it can influence test results. We developed an LC-MRM-MS test to molecularly characterize antithrombin in citrate plasma. The test principle differs greatly from traditional laboratory tests and the influence of varying plasma sample matrices is largely unknown.

Objectives

To identify whether variations in sample matrix affect the LC-MRM-MS test for antithrombin and assess whether sample pre-processing by immunocapture reduces matrix-specific effects.

Methods

Samples (n = 45) originating from four different blood collection tubes (sodium citrate, lithium heparin, K₂-EDTA and K₂-EDTA with protease inhibitors) were processed directly or after immunocapture. Antithrombin was digested into proteotypic peptides, which were monitored by LC-MRM-MS. Results from lithium heparin and the K₂-EDTA matrices were compared to the standard sample matrix, sodium citrate, using Deming regression analysis and repeated measures one-way ANOVA.

Results

Deming regression analysis of directly processed samples revealed slopes deviating >5% from the line of identity for at least six out of 22 peptides in all matrices. Significant differences between all matrices were found upon analysis by ANOVA for at least 10 peptides. Pre-processing by immunocapture led to slopes within 5% of the line of identity for nearly all peptides of the matrices. Furthermore, significant differences between matrices after immunocapture were only observed for four peptides.

Conclusion

Variations in the sample matrix affect the measurement of antithrombin by LC-MRM-MS, but observed effects are greatly reduced upon pre-processing by immunocapture.

Time-dependent diagnostic performance of a rapid troponin T version 2 bedside test in patients with acute coronary syndromes

In a prospective trial, the diagnostic performance of the second version of the troponin T rapid assay (Trop T; cutoff 0.2 microg/L) was compared with the quantitative cardiac-specific troponin T assay (cTnT ELISA; cutoff 0.1 microg/L) and other established cardiac markers such as CK, CK-MB activity, CK-MB mass and myoglobin. Additionally, a 30-day follow-up was performed to determine the suitability of the Trop T assay and the reference markers for short-term risk stratification. Two-hundred-and-eighty-six consecutive patients with chest pain and suspected acute myocardial infarction (AMI) were enrolled in two CCU departments. Serial blood specimens were taken at admission and at 3, 6, 12, 24, 48, 72 and 96 h after admission. According to the biochemical criterion CK-MB mass, the patients were classified as having AMI in 154 patients (54%), unstable angina (UAP) in 72 patients (27%) and no evidence for acute cardiac ischemia in 55 patients (19%). Analytical method comparison of Trop T with cTnT ELISA (cutoff 0.1 microg/L) showed a good agreement, Trop T yielded only 4% false-negative and 3% false-positive results. The diagnostic performance of Trop T for the detection of AMI was only slightly inferior compared to cTnT ELISA. Beyond 12 h after admission, Trop T and cTnT ELISA maintained a sensitivity close to 100%, whereas the sensitivity of the other cardiac markers decreased sharply. The diagnostic sensitivity of Trop T for the detection of minor myocardial damage in UAP patients was the same as for cTnT ELISA. Death within 30 days' follow-up occurred only in AMI patients with a positive Trop T test result within the first 6 h after admission. The admission Trop T and cTnT ELISA were the only significant biochemical predictors of major cardiac events. In conclusion, these data show that Trop T has similar diagnostic sensitivity as cTnT ELISA and is a useful tool to confirm acute or subacute myocardial infarction. Trop T is an excellent marker in detecting minor myocardial damage in UAP patients and is suitable for short-term risk stratification.

Long-term prognostic value of serial troponin T bedside tests in patients with acute coronary syndromes

The early presence of troponin T in serum strongly predicts short-term mortality and myocardial infarction in patients with acute coronary syndromes. We investigated the long-term outcome of the prognostic significance of the troponin T rapid bedside assay (TROPT) and compared this with the quantitative troponin T assay (cTnT enzyme-linked immunosorbent assay), myoglobin and creatine kinase-MB (CK-MB) mass. One hundred sixty-three patients with chest pain and suspected acute coronary syndromes were studied and followed prospectively for 3 years. Serial blood specimens were obtained at admission and at 3, 6, 12, 24, 48, 72, and 96 hours after admission. Patients were classified as having acute myocardial infarction in 99 patients (61%), unstable angina in 34 patients (21%), and no evidence for acute cardiac ischemia in 30 patients (18%). At 3 years, 28 patients (17%) had died of which 25 deaths (15%) were for cardiac reasons. Twenty-one patients (13%) had a nonfatal (recurrent) myocardial infarction. At admission 29% of the patients were TROPT positive (> or = 0.2 microg/L), another 31% became positive within 12 hours, and 39% remained negative. When adjusted for baseline variables, a positive TROPT (any sample 0 to 12 hours) was independently associated with a higher risk of cardiac mortality (RR 4.3, 95% confidence interval [CI] 1.3 to 14.0). Because troponin T stays elevated up to 2 weeks, later TROPT results between 24 and 96 hours remained significantly predictive for mortality. The cTnT enzyme-linked immunosorbent assay (any sample 0 to 12 hours; cutoff > or = 0.2 microg/L) was similarly predictive (RR 2.9, 95% CI 1.0 to 8.6). Early myoglobin results were significantly prognostic for cardiac mortality up to 12 hours after admission (RR 3.7; 95% CI 1.0 to 12.0). In contrast, serial CK-MB mass measurements were not predictive of mortality. Thus, a combination of a baseline TROPT and an additional TROPT 12 hours or later identifies a subgroup of patients at high risk for subsequent mortality and reinfarction, both at short-term but also at long-term.

Analytical and clinical performance of a detergent-based homogeneous LDL-cholesterol assay: a multicenter evaluation

BACKGROUND

LDL-cholesterol (LDL-C) concentrations currently are determined in most clinical laboratories using the Friedewald calculation. This approach has several limitations and may not always meet the current total error recommendation in LDL-C measurement of </=12% established by the National Cholesterol Education Program.

METHODS

In a multicenter study, we evaluated the analytical and clinical performance of a homogeneous LDL-C assay (LDL-C(Roche); Roche Diagnostics, Indianapolis, IN) in a comparison with a beta-quantification method.

RESULTS

This direct assay correlated highly with a beta-quantification method (r = 0.968; y = 1.037x - 95.8 mg/L; n = 355; 95% confidence intervals, 1.011-1.063 for the slope and -129.5 to 62.0 mg/L for the y-intercept) and met the current total error requirement. The assay was not affected significantly by concentrations of hemoglobin up to 6000 mg/L or bilirubin up to 500 mg/L. However, a negative bias of 10% was seen when triglyceride concentrations exceeded 10 000 mg/L. At the medical decision cut-point range, the LDL-C(Roche) assay showed positive predictive values of 91-100% and negative predictive values of 80-99%. Furthermore, the clinical utility of the assay seemed unaffected in samples obtained postprandially.

CONCLUSIONS

The homogeneous LDL-C(Roche) assay meets the currently established analytical performance goals and may be useful for the diagnosis and management of hyperlipidemic patients.

A new liquid homogeneous assay for HDL cholesterol determination evaluated in seven laboratories in Europe and the United States

We evaluated a new liquid homogeneous assay for the direct measurement of high density lipoprotein cholesterol (HDL-C Plus) in seven laboratories. The assay includes two reagents which can be readily used in most available clinical chemistry analyzers. The total CVs of the new method were below 4.6% and the bias in relation to the designated comparison method was below 3.9%. The total error ranged between 4 to 7%. HDL-C values determined by this method were in good agreement with those obtained by the old homogeneous assay using lyophilized reagents, and other homogeneous and precipitation assays (0.944 < r < 0.996). The assay was linear up to at least 3.89 mmol/l HDL-C. Hemoglobin did not interfere, whereas in icteric samples slight deviations were observed. Lipemia up to 11.3 to 22.6 mmol/l triglycerides did not interfere with this homogeneous HDL-C assay. In samples of patients with paraproteinemia, discrepant results were seen. This liquid homogeneous HDL-C assay was easy to handle and produced similar results in all laboratories participating in this study. This method will enable clinical laboratories to reliably measure HDL-C for risk assessment of coronary heart disease.

Precision, accuracy and linearity of radiometer EML 105 whole blood metabolite biosensors

The analytical performance of a new, whole blood glucose and lactate electrode system (EML 105 analyser. Radiometer Medical A/S. Copenhagen, Denmark) was evaluated. Between-day coefficients of variation were < or = 1.9% and < or = 3.1% for glucose and lactate, respectively. Recoveries of glucose were 100 +/- 10% using either aqueous or protein-based standards. Recoveries of lactate depended on the matrix, being underestimated in aqueous standards (approximately -10%) and 95-100% in standards containing 40 g/L albumin at lactate concentrations of 15 and 30 mmol/L. However, recoveries were high (up to 180%) at low lactate concentrations in protein-based standards. Carry-over, investigated according to National Clinical Chemistry Laboratory Standards EP10-T2, was negligible (alpha = 0.01). Glucose and lactate biosensors equipped with new membranes were linear up to 60 and 30 mmol/L, respectively. However, linearity fell upon daily use with increasing membrane lifetime. We conclude that the Radiometer metabolite biosensor results are reproducible and do not suffer from specimen-related carry-over. However, lactate recovery depends on the protein content and the lactate concentration.

Reference standardization and analytical performance of a liquid homogeneous high-density lipoprotein cholesterol method compared with chemical precipitation method

BACKGROUND

The use of high-density lipoprotein cholesterol (HDL-C) levels as a risk factor for coronary heart disease necessitates an accurate and precise method for measuring HDL-C. The Centers for Disease Control and Prevention HDL-C reference method (RM) and designated comparison method (DCM) are time-consuming, expensive, and impractical for routine clinical use. We evaluated the Liquid N-geneous (LN-gen) HDL-C assay (Genzyme Diagnostics, Cambridge, Mass) to determine if this homogeneous reagent meets the National Cholesterol Education Program requirements for HDL-C evaluation.

DESIGN

Accuracy of the LN-gen HDL-C assay was compared in combination with phosphotungstic acid (PTA) precipitation with DCM HDL-C for normotriglyceridemic serum specimens (triglycerides < 2.0 g/L) and with RM HDL-C for specimens with triglycerides levels > or = 2.0 g/L.

SETTING

Genzyme Diagnostics (with RM and DCM assayed by Pacific BioMetrics Inc, Seattle, Wash) and the Lipid Reference Laboratory of the University Hospital Rotterdam, The Netherlands.

RESULTS

Linear regression to DCM (n = 90) was (LN-gen = 1.015 DCM + 0.01 g/L, r = 0.993, SE = 0.015 g/L) and (PTA = 1.004 DCM - 0.017 g/L, r = 0.980, SE = 0.025 g/L), with a mean percent bias to DCM of 3.3% and -2.8% for LN-gen and PTA, respectively. The comparison with RM (n = 69) showed an increased mean bias for PTA (-5.8%) as compared with LN-gen (1.5%). The correlation and regression equations were (LN-gen = 1.020 RM - 0.002 g/L, r = 0.985, SE = 0.017 g/L) and (PTA = 1.042 RM - 0.032 g/L, r = 0.984, SE = 0.018 g/L). The precision of LN-gen was confirmed at < 2.1% coefficient of variation, and the total error was calculated to be < or = 7.7% for both normotriglyceride and elevated triglyceride specimens at HDL-C decision points of 0.35 g/L and 0.60 g/L.

CONCLUSIONS

The LN-gen HDL-C assay offers a cost-effective convenient method for meeting the 1998 precision, bias, and total error recommendations of the National Cholesterol Education Program.

Survey of total error of precipitation and homogeneous HDL-cholesterol methods and simultaneous evaluation of lyophilized saccharose-containing candidate reference materials for HDL-cholesterol

BACKGROUND

Standardization of HDL-cholesterol is needed for risk assessment. We assessed for the first time the accuracy of HDL-cholesterol testing in The Netherlands and evaluated 11 candidate reference materials (CRMs).

METHODS

The total error (TE) of HDL-cholesterol measurements was assessed in native human sera by 25 Dutch clinical chemistry laboratories. Concomitantly, the suitability of lyophilized, saccharose-containing CRMs (n = 11) for HDL-cholesterol was evaluated.

RESULTS

In the precipitation method group, which included 25 laboratories and four methods, the mean (minimum-maximum) TE was 11.5% (2.7-25.2%), signifying that 18 of 25 laboratories satisfied the TE goal of </=13% issued by the National Cholesterol Education Program (NCEP). In the homogeneous HDL-cholesterol method group, which included five laboratories, each performing two different methods, the mean (minimum-maximum) TE was 9.5% (6.0-17.3%) for the Boehringer assay and 15.7% (3.3-30.7%) for the Genzyme assay. For the Boehringer homogeneous assay, one of five laboratories did not meet the TE criterion, whereas for the Genzyme homogeneous assay, three of five laboratories exceeded the 13% criterion. The biases on the HDL-cholesterol values found by various precipitation methods were highly variable in all CRMs, irrespective of the quality, whereas the biases found by the homogeneous method from Boehringer were far less than +/-5% for the highest-quality CRMs (CRMs 4-6).

CONCLUSIONS

The NCEP goal was met by 24 of 35 laboratories assessed by use of native human sera. Selectively pooled, lyophilized CRMs that are cryoprotected with 200 g/L saccharose have ample potential for use in the standardization of homogeneous HDL-cholesterol methods.

Regional serum cholesterol differences in Belgium: do genetically determined cardiovascular risk factors contribute?

BACKGROUND

Differences in serum lipid distribution and mortality from ischaemic heart disease have repeatedly been reported between Belgian northerners and southerners. We investigated whether serum lipoprotein(a) (Lp(a)) and apolipoprotein (apo) E polymorphism were involved.

METHODS

Fasting serum lipids, apo A-I and B, and Lp(a) levels were examined in randomly selected, 20-39 year old Belgian males and females from the north (Flanders) and the south (Wallonia) of Belgium (N = 900). Apo E phenotype distribution was investigated in random subsamples from either region (N = 249).

RESULTS

Mean serum cholesterol, low density lipoprotein cholesterol (LDL-c), apo B and triglyceride levels were higher in Walloons compared to Flemings within each gender, the difference being significant in 30-39 year old males. Average high density lipoprotein cholesterol and apo A-I levels were significantly lower in 30-39 year old male southerners, compared to their northern counterparts. Median Lp(a) was 67 mg/l in northerners and 75 mg/l in southerners (NS). The apo E phenotype distribution was similar in both regions (chi2 = 7.213; d.f. = 5; P = 0.2053), whereas the average effects of the apo E alleles differed between the regions. In southerners the epsilon4 effect upon adjusted apo B and LDL-c levels was approximately+12% and the epsilon2 effect was approximately-15%; in northerners the epsilon4 and epsilon2 effects were approximately+5% and approximately-25%, respectively. The apo E polymorphism did not affect serum Lp(a) levels.

CONCLUSIONS

Regional cholesterol differences between Flemings and Walloons cannot be explained by differences in serum Lp(a) or apo E phenotype distribution. The less favourable epsilon2 and epsilon4 effects in southerners compared to northerners reflect modulation of the apo E gene by particular environments.

Reference standardization and triglyceride interference of a new homogeneous HDL-cholesterol assay compared with a former chemical precipitation assay

A homogeneous HDL-c assay (HDL-H), which uses polyethylene glycol-modified enzymes and sulfated alpha-cyclodextrin, was assessed for precision, accuracy, and cholesterol and triglyceride interference. In addition, its analytical performance was compared with that of a phosphotungstic acid (PTA)/MgCl2 precipitation method (HDL-P). Within-run CVs were < or = 1.87%; total CVs were < or = 3.08%. Accuracy was evaluated in fresh normotriglyceridemic sera using the Designated Comparison Method (HDL-H = 1.037 Designated Comparison Method + 4 mg/L; n = 63) and in moderately hypertriglyceridemic sera by using the Reference Method (HDL-H = 1.068 Reference Method - 17 mg/L; n = 41). Mean biases were 4.5% and 2.2%, respectively. In hypertriglyceridemic sera (n = 85), HDL-H concentrations were increasingly positively biased with increasing triglyceride concentrations. The method comparison between HDL-H and HDL-P yielded the following equation: HDL-H = 1.037 HDL-P + 15 mg/L; n = 478. We conclude that HDL-H amply meets the 1998 NCEP recommendations for total error; its precision is superior compared with that of HDL-P, and its average bias remains below +/-5% as long as triglyceride concentrations are < or = 10 g/L and in case of moderate hypercholesterolemia.

Lipoprotein(a) changes during and after coronary artery bypass grafting: an epiphenomenon?

The lipoprotein(a) (Lp(a)) time course during and after coronary artery bypass grafting was examined in 20 caucasoid patients, in relation to the time courses of serum cholesterol and serum triglycerides. Samples were taken at eight different time points. Baseline geometric means (SD) for Lp(a), cholesterol and triglycerides were 115 (336) mg/L, 5.73 (1.10) mmol/L and 1.73 (1.21) mmol/L, respectively. Up to 10 min after cardiopulmonary bypass (CPB) and after correction for haemodilution, no observable effect of CPB on serum concentrations of Lp(a) could be demonstrated, whereas serum concentrations of total cholesterol and triglycerides showed a progressive and significant decline. Ten minutes after stopping CPB geometric means for cholesterol and triglyceride were 3.90 (0.82) and 0.90 (0.58) mmol/L, respectively. At the third post-operative day geometric Lp(a) and cholesterol means decreased to 62(90) mg/L and 2.97 (0.84) mmol/L, respectively, while triglycerides went up. It is concluded that Lp(a) levels remain constant during CPB, but mimic total cholesterol changes in the post-CABG period.

Modulation of lipoprotein(a) atherogenicity by high density lipoprotein cholesterol levels in middle-aged men with symptomatic coronary artery disease and normal to moderately elevated serum cholesterol. Regression Growth Evaluation Statin Study (REGRESS) Study Group

OBJECTIVES

This study sought to examine whether lipoprotein(a) levels predict coronary artery lumen changes in patients with symptomatic coronary artery disease (CAD) and normal to moderate hypercholesterolemia.

BACKGROUND

Recent conflicting reports have confirmed or refuted the association of lipoprotein(a) with clinical events or angiographically verified disease progression.

METHODS

The association between serum lipoprotein(a) and changes in coronary artery lumen was studied in 704 men entered into the Regression Growth Evaluation Statin Study (REGRESS), a double-blind, placebo-controlled, quantitative angiographic study that assessed the effect of 2 years of pravastatin treatment. The primary end points were changes in average mean segment diameter (MSD) and average minimal obstruction diameter (MOD). Pravastatin- and placebo-treated patients were classified as having progressing, regressing or stable CAD, and median lipoprotein(a) concentrations were compared. Bivariate and multivariate regression analyses were performed in the overall patient group and in high risk subgroups.

RESULTS

Pravastatin treatment did not affect serum apolipoprotein(a) levels. Median in-trial (sampled at 24 months) apolipoprotein(a) levels for regressing, stable and progressing CAD were, respectively, 130, 162 and 251 U/liter in placebo-treated patients and 143, 224 and 306 U/liter in pravastatin-treated patients. Predictors of MSD and MOD changes were baseline MSD and MOD, in-trial apolipoprotein(a), in-trial high density lipoprotein (HDL) cholesterol and baseline use of long-acting nitrates. The multivariate models predicted 14% of MSD changes and 12% of MOD changes; apolipoprotein(a) predicted only 2.6% and 4.8%, respectively. However, in patients with in-trial HDL cholesterol levels <0.7 mmol/liter, apolipoprotein(a) predicted up to 37% of the arteriographic changes.

CONCLUSIONS

Serum lipoprotein(a) levels predict coronary artery lumen changes in normal to moderately hypercholesterolemic white men with CAD; its atherogenicity is marked in the presence of concomitant hypoalphalipoproteinemia.

Significance of various parameters derived from biological variability of lipoprotein(a), homocysteine, cysteine, and total antioxidant status

Analytical and biological components of variability and various derived indices have been determined for lipoprotein(a) [Lp(a)], homocysteine (Hcy), cysteine (Cys), and total antioxidant status (TAOS) in ostensibly healthy adult Caucasians and in stable outpatients with an increased serum Lp(a). In healthy Caucasians, average intraindividual biological CVs (CVb) were 20.0% for Lp(a), 9.4% for Hcy, 5.9% for Cys, and 2.8% for TAOS, CVbs being similar in men and women. In the outpatient group, CVbs were comparable for Hcy, Cys, and TAOS, but significantly lower for Lp(a) (7.5% vs 20.0%; P <0.0001). Moreover, a significant inverse relation between both biological and analytical CVs (CVa) and serum Lp(a) concentrations was demonstrated. We conclude that average CVa and CVb values, and hence average derived indices, are adequate for Hcy, Cys, and TAOS, whereas individual values should be used for Lp(a).

Serum LP(a) levels in African aboriginal Pygmies and Bantus, compared with Caucasian and Asian population samples

Serum lipoprotein(a) (Lp(a)) and its correlates were studied in African Aboriginal Pygmies (n = 146) and Bantus (n = 208) from Cameroon. Geometric mean Lp(a) levels were 274 and 289 mg/l in Bantu males and females, respectively, and 220 and 299 mg/l in Pygmy males and females, the gender difference being significant in Pygmies (p = 0.024). In Pygmies 41% and 52% of the males and females, respectively, had Lp(a) levels above 300 mg/l, compared with 47% and 55% in Bantus. Overall, Lp(a) levels did not significantly differ between Pygmies and Bantus, and did not correlate with age, body mass index (BMI), systolic and diastolic blood pressure. Compared with healthy Asian and Caucasian population samples, age- and BMI-adjusted geometric Lp(a) means were 2.3- to 5.0-fold higher in Pygmy and Bantu males, and 2.9- to 3.6-fold higher in Pygmy and Bantu females (p < or = 0.05). Across the population samples studied ethnicity predicted 12% and 17% of serum Lp(a) variance in males and females, respectively.

Multicenter evaluation of a homogeneous assay for HDL-cholesterol without sample pretreatment

We evaluated a new homogeneous assay for the measurement of HDL-cholesterol (HDL-C) in six European laboratories. The assay includes two reagents and is applicable to most autoanalyzers, which allows full automation. The total CVs of the new method ranged between 1.3% and 6.7%. Thereby determined HDL-C values were in good agreement with those obtained by precipitation with phosphotungstic acid/MgCl2 or by a combination of ultracentrifugation and precipitation (0.956 < r < 0.994). The assay was linear up to at least 1500 mg/L HDL-C. Hemoglobin did not interfere, whereas icteric samples with bilirubin > 100 mg/L showed discrepancies between the homogeneous and the precipitation assay. Lipemia up to total triglyceride concentrations of 8000 mg/L did not interfere with the homogeneous HDL-C assay. The homogeneous HDL-C assay was easy to handle and produced similar results in all laboratories participating in this study. This method will significantly facilitate the screening of individuals at increased risk for cardiovascular disease.

Thrombolysis-induced coronary reperfusion causes acute and massive interstitial release of cardiac muscle cell proteins

OBJECTIVE

Reperfusion of the infarct-related artery in patients with acute myocardial infarction limits infarct size, but also causes accelerated release into plasma of cardiac tissue proteins. The latter effect could reflect either enhanced protein washout from the heart or abrupt disruption of myocyte membranes. The present study indicates that the latter mechanism prevails.

METHODS

In 26 patients, patency of the infarct-related artery was determined by coronary angiography 90 min and 5-7 days after thrombolytic treatment. Continuous electrocardiography was performed during the first 24 h after admission. Cumulative release of myoglobin (Mb) and creatine kinase (CK) into plasma was calculated from frequently sampled plasma concentrations.

RESULTS

In patients with a patent infarct-related artery after 90 min, onset of a rapid (> 50%) decrease in ST-vector magnitude coincided with an equally rapid increase in QRS-vector magnitude, and with a sudden onset of release into plasma of Mb as well as CK. In these patients, a maximal initial release rate was observed and cumulative release conformed closely to a simple model for sudden interstitial liberation of proteins. In contrast, protein release started more gradually and could not be fitted to this model, in patients with persistent occlusion of the infarct-related artery at 90 min and absence of ST-vector normalisation.

CONCLUSIONS

Previous studies have demonstrated significant myocardial salvage by timely reperfusion therapy. Nevertheless, this study indicates that the moment of recanalisation of the infarct-related artery coincides with sudden and massive disruption of myocyte membranes. Attenuation of this effect, if possible, could further improve the benefits of reperfusion therapy.

Oral physiological magnesium supplementation for 6 weeks with 1 g/d magnesium oxide does not affect increased Lp(a) levels in hypercholesterolaemic subjects

Twenty hyperlipidaemic patients on a cholesterol-poor diet were selected on the basis of a raised lipoprotein (a) (Lp(a); apo (a) > 300 U/litre) and treated with 1000 mg MgO per day during 6 weeks. Serum magnesium slightly increased compared to pretreatment levels (P < 0.001). Serum apo(a) concentrations (mean +/- S.D.) were not affected: pretreatment level 963 +/- 552 U/litre; during treatment 999 +/- 536 U/litre; and after washout 995 +/- 524 U/litre. Serum cholesterol increased slightly during MgO treatment because of an increase in LDL-cholesterol (10 per cent) and returned to pretreatment levels after a washout period.

Performance of a direct, immunoseparation based LDL-cholesterol method compared to Friedewald calculation and a polyvinyl sulphate precipitation method

The analytical performance of a direct, immunoseparation based LDL-cholesterol method (Genzyme Corporation) was evaluated on an ELAN analyser (Merck), and compared with the performance of routinely used methods (LDL-cholesterol estimated by the Friedewald equation, and LDL-cholesterol obtained after polyvinyl sulphate precipitation). Within-day coefficients of variation (CVs) were 0.79 to 2.51% for immunoseparation based LDL-cholesterol; the between-day CVs varied between 2.62 and 3.89%, i.e. within the recommended National Cholesterol Education Program (NCEP) goal of < 4%. A method comparison study, according to the National Committee for Clinical Laboratory Standards (NCCLS) EP9-P guidelines, was performed using fasting normo- and hypertriacylglycerolaemic as well as cholestatic sera. In fresh normotriacylglycerolaemic sera immunoseparation based LDL-cholesterol (y) and Friedewald LDL-cholesterol (x) values were identical as slope and intercept of the Passing & Bablok regression equation were not significantly different from one and zero, respectively (y = 1.006 x -0.107; N = 45). In contrast, immunoseparation based LDL-cholesterol (y) differed significantly from polyvinyl sulphate LDL-cholesterol (x) results (y = 0.922 x + 0.234; N = 103). Freezing normotriacylglycerolaemic sera (three weeks, -20 degrees C) resulted in a negative bias of -5.8% for the immunoseparation based LDL-cholesterol method, and in a positive bias of +5.3% for the polyvinyl sulphate method, compared to fresh specimens. Immunoseparated LDL-cholesterol was completely recovered up to at least 37.84 mmol/l serum triacylglycerols. We conclude that the immunoseparation based LDL-cholesterol method is a practical, not technically demanding technique well applicable within routine clinical laboratories.(ABSTRACT TRUNCATED AT 250 WORDS)

Pubertal serum lipoprotein (a) and its correlates in Belgian schoolchildren

BACKGROUND

Serum lipoprotein (a) (Lp(a)) is an independent risk factor for premature coronary artery disease in Caucasians. Generally Lp(a) serum levels remain fairly constant throughout an individual's life, but are presumably modulated by sex hormones. This study documents the distribution and correlates of serum Lp(a) during sexual maturation in Belgian children. A comparison with Lp(a) levels in Belgian adults is made.

METHODS

Serum Lp(a), lipid and apolipoprotein A-I and B levels were determined cross-sectionally in 266 Belgian schoolchildren and adolescents in relation to sexual maturation, anthropometrics and socioeconomic status. Sexual maturity was scored according to Tanner's classification.

RESULTS

Median Lp(a) levels were 82, 117, 110, 100 and 73 mg/l at the five subsequent genital development stages in boys (ANOVA, P = 0.816), and 73, 78, 204, 110 and 114 mg/l at the five breast development stages in girls (ANOVA, P = 0.087). The Lp(a) distributions in boys and girls were skewed to the right, overall medians being 82 and 94 mg/ml (P = 0.2537). The 90th and 95th percentiles were 515 and 712 mg/l respectively. The geometric Lp(a) mean in children was significantly higher compared to that in 683 sex-matched Belgian adults (89 mg/l versus 69 mg/l, P = 0.006). Multiple linear regression pointed out that developmental age, chronological age, body mass index and/or systolic blood pressure predicted serum lipid and apolipoprotein levels, but none of the Lp(a) variance.

CONCLUSION

Pubertal stage was not correlated with Lp(a) levels in Belgian schoolchildren, supporting the contention that serum Lp(a) is predominantly genetically controlled.

Evaluation of the Cholestech L.D.X. desktop analyser for cholesterol, HDL-cholesterol, and triacylglycerols in heparinized venous blood

The analytical performance of the Cholestech L.D.X. lipid analyzer for total and HDL-cholesterol and triacylglycerols in heparinized venous blood was evaluated, using two Cholestech L.D.X. analysers and two reagent cassette lots. Within-day and day-to-day precision were checked with commercial quality control sera. Within-day coefficients of variation (CVs) were 2.0 to 4.7% for total cholesterol, 3.4 to 5.5% for HDL-cholesterol, and 2.1 to 4.8% for triacylglycerols. Between-day CVs were < or = 6.0% for triacylglycerols, and < or = 7.0% for HDL-cholesterol. A method comparison study, according to the NCCLS EP9-P guidelines, was performed for all three analytes. Cholestech whole blood values (y) were compared with serum values (x) generated by a standardized enzymatic method for cholesterol, and by current state-of-the-art methodology for HDL-cholesterol and triacylglycerols. Correlation coefficients were all > 0.98. Mean slopes and intercepts for the Passing & Bablok regression equations of total and HDL-cholesterol were not significantly different from one and zero, respectively. Overall, the Cholestech means differed by < 1.8% for total cholesterol, and < 5% for HDL-cholesterol versus the comparison method means. For total cholesterol the National Cholesterol Education Program (NCEP) requirements for accuracy and precision of < or = 3% were met. For triacylglycerols, significant negative intercepts ranging from -0.26 to -0.33 mmol/l were observed, with slopes significantly greater than one.

Noninvasive assessment of reperfusion and reocclusion after thrombolysis in acute myocardial infarction

The clinical significance of ST-segment changes and of the time course of appearance in serum of different cardiac proteins has been reviewed for the diagnosis of coronary reperfusion and reocclusion after thrombolysis. In particular, the value of serial 12-lead electrocardiographic (ECG) studies, of Holter monitoring, and of continuous multilead computer-assisted ECG monitoring is compared. Regarding the serum proteins, the clinical significance of reperfusion indices described so far for serum creatine kinase (CK), its isoenzyme serum creatinine kinase MB, the CK isoforms, and myoglobin is reviewed. Emphasis is placed on (1) the calculation method used for deriving the reperfusion indices; (2) the sensitivity and the specificity of the reperfusion indices; (3) the minimum turn-around time needed to produce the reperfusion indices (depending on the practicability of the analytical and calculation methods and their applicability in an emergency laboratory); (4) the ability of the indices to produce reliable estimates of reperfusion efficacy of the thrombolytic agents under study; and (5) the ability of the marker proteins to detect reinfarction as well as the suitability of the markers to detect real-time necrosis.

The effects of weight loss and apolipoprotein E polymorphism on serum lipids, apolipoproteins A-I and B, and lipoprotein(a)

Serum levels of lipoprotein(a) [Lp(a)], an independent risk factor for coronary heart disease, are strongly influenced by genetic factors. To evaluate the effect of weight loss on serum Lp(a), 54 normolipidemic obese women were examined before and after a two-month weight reduction programme. A mean weight loss of 10.1 kg was associated with decreases of serum triglycerides, total cholesterol (TC), LDL-C, HDL-C, apo B and apo A-I (P = 0.0001 for all variables), but not Lp(a). However, initial Lp(a) values were related to Lp(a) responses during dietary intervention (P = 0.0001). In subjects with pre-treatment Lp(a) values above 30 mg/dl, a mean 26.3% decrease was observed with weight loss, while no change was found in subjects with low Lp(a) values at baseline (P = 0.007 for group comparison). Apo E polymorphism contributes to the variation in lipid levels in the general population and in the obese. The relative contributions of the apo E locus to the total variance of TC, LDL-C and Lp(a) at baseline in these obese women were estimated to be 3.3, 1.7 and 3.2%, respectively, which are less than previously reported in healthy adults. Pre-treatment TC was increased in subjects with the apo E 3/4 phenotype compared to those with the common apo E 3/3 phenotype (P = 0.03). Apo E polymorphism did not affect Lp(a) levels at baseline nor the changes in lipoprotein variables, including Lp(a), during weight loss. In conclusion, short-term substantial weight loss in normolipidemic obese women resulted in a lowering of Lp(a) only in individuals with pre-treatment Lp(a) levels above 30 mg/dl.(ABSTRACT TRUNCATED AT 250 WORDS)

Different effect of Intralipid and triacylglycerol rich lipoproteins on the Kodak Ektachem serum cholesterol determination

We documented the quantitative effects of lipaemia on cholesterol recovery on a Kodak Ektachem 700 XRC analyser (Rochester, NY, USA) in comparison with a Hitachi 717 analyser (Boehringer, Mannheim, Germany). Using the linear ranges of the analysers, we compared the effects of adding Intralipid and of adding high concentrations of native Very-Low-Density-Lipoproteins and/or chylomicrons. Our data demonstrate less than 10% bias for the Kodak cholesterol determination in an Intralipid dilution series prepared according to M. R. Glick and coworkers (e.g. Clin. Chem. 33 (1987) 1453-1458). However, in a hypertriglyceridaemic dilution series (theoretical cholesterol concentrations ranged from 5.2 to 15.5 mmol/l) the Kodak cholesterol recovery fraction decreased from 0.88 to 0.58 when the triacylglycerol concentration increased from 5.64 mmol/l to 38.35 mmol/l. In contrast, the cholesterol recoveries on the Hitachi analyser were complete for both approaches. We conclude that the lipaemia effect on the Kodak cholesterol determination is not adequately reflected by addition of Intralipid, because the Kodak cholesterol determination is more prone to interference by turbidity when triacylglycerols are presented as native serum lipoproteins, especially as chylomicrons.

Serum lipoprotein(a) levels in racially different populations

Lipoprotein(a) is an atherogenic lipoprotein which has been studied predominantly in white populations. Serum lipoprotein(a), serum lipids, and apolipoproteins A-I and B were quantified in 1991 in a total of 300 sex-matched samples derived from five different ethnic groups. Three population samples of Asian origin (Tibet, Korea, and China), one population sample of West African origin (Nigeria), and one Western population sample (Belgium) were included. All serum samples had been collected in the past (3-11 years previously) and had been stored at -80 degrees C since then. Thirty serum samples from males and 30 serum samples from females were analyzed from each ethnic group. Overall median lipoprotein(a) levels in Koreans, Chinese, Tibetans, Nigerians, and Belgians were 99, 89, 49, 134, and 80 mg/liter, respectively. Lipoprotein(a) frequency distributions were highly skewed to the right in all populations, with the Nigerian distribution showing less skewness than the Asian and Western plots. All distributions became nearly gaussian after logarithmic transformation. No statistical difference was found between the mean log lipoprotein(a) values of the sexes (4.43 +/- 1.01 mg/liter (standard deviation) in men; 4.44 +/- 1.08 mg/liter in women). Pearson correlation analysis of both sexes combined revealed no statistically significant correlation (at the p less than 0.01 level) of log lipoprotein(a) with age, height, weight, body mass index, cholesterol, high density lipoprotein cholesterol, apolipoprotein A-I, or apolipoprotein B within any of the population groups studied or after pooling of all population groups.

Macroamylasemia in a 5-year-old girl

In macroamylasemia, a macromolecular complex consisting of amylase linked to immunoglobulins circulates in the plasma and usually causes benign hyperamylasemia with low or normal amylasuria. Macroamylasemia is extremely rare in pediatric patients as it has been described in only four patients. We report herein the case of a 5-year-old girl with abdominal pain and macroamylasemia. To recognize macroamylase, we used agar gel electrophoresis, PEG precipitation, and fast protein liquid chromatography (FPLC). In our case, FPLC was found to be the most reliable method for the identification of the macromolecular complex. Macroamylasemia is merely a biochemical abnormality that is not associated with any kind of pathology. Its identification is therefore essential in order to avoid a wrong diagnosis, i.e., pancreatitis, with consequent inappropriate therapies.