Papers by Christa Cobbaert
Clinical Chemistry, Apr 1, 2000
Background: LDL-cholesterol (LDL-C) concentrations currently are determined in most clinical labo... more 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 -quantification method. Results: This direct assay correlated highly with a -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.
Clinical Chemistry and Laboratory Medicine, Jul 20, 2019
Background: High-sensitivity cardiac troponin T/I (hs-cTnT/I) assays have improved analytical sen... more Background: High-sensitivity cardiac troponin T/I (hs-cTnT/I) assays have improved analytical sensitivity for the detection of myocardial infarction (MI). To gain clinical specificity and sensitivity, interpretation of changes in cTn concentrations over time is crucial. The 2015 ESC NSTEMI guideline defines absolute delta values as additional rule-in and rule-out criteria for MI. A critical assumption for application of this rule is that total analytical imprecision within the delta period, including interinstrument bias, is comparable to analytical imprecision in the validation studies. Methods: Data from the Dutch External Quality Assessment Scheme (EQAS) were used to calculate inter-instrument bias and estimate imprecision for the measuring range where the proposed delta values are relevant: for Roche Elecsys hs-cTnT, 5-52 and 5-12 ng/L; for Abbott Architect hs-cTnI, 2-52 and 2-5 ng/L for rule-in and ruleout, respectively. Results: For Elecsys, the median inter-instrument bias is 0.3 ng/L (n = 33 laboratories), resulting in reference change values (RCVs) of 3.0 and 1.7 ng/L, respectively, for rule-in and rule-out with imprecision as claimed by the manufacturer. With RCVs smaller than the guideline's delta thresholds, 100% of the laboratories have adequate specifications. RCVs for rule-in/rule-out increased to 4.6 ng/L/2.5 ng/L, respectively, with individual imprecisions as estimated from EQA data, resulting in 64% and 82% of laboratories with adequate specifications. For Architect, 40% of instruments (n = 10) might falsely qualify the result as clinically relevant; hence, inter-instrument bias could not be determined. We advise laboratories that use the fast 0/1-h algorithm to introduce stringent internal quality procedures at the relevant/low concentration level, especially when multiple analyzers are randomly used.
Evaluation of Interspecimen Trypsin Digestion Efficiency Prior to Multiple Reaction Monitoring-Based Absolute Protein Quantification with Native Protein Calibrators
Journal of Proteome Research, Nov 13, 2013
Chapter 1 General introduction 9 Chapter 2 Effect of long-term sample storage on the assay of lip... more Chapter 1 General introduction 9 Chapter 2 Effect of long-term sample storage on the assay of lipoprotein(a) by immunoradiometric and enzyme-linked inununosorbent assay kits 23 Chapter 3 Significance of various parameters derived from biological vmiability of lipoprotein(a), homocysteine, cysteine and Total Anti-Oxidant Status 37 Clin Chon; accepted Chapter 9 Modulation of lipoprotein(a) atherogenicity by HDL cholesterol levels in middle-aged men with symptomatic coronaty artery disease and normal to moderately elevated serum cholesterol
Advances in laboratory medicine, Aug 8, 2020
Reference intervals are commonly used as a decision-making tool. In this review, we provide an ov... more Reference intervals are commonly used as a decision-making tool. In this review, we provide an overview on "big data" and reference intervals, describing the rationale, current practices including statistical methods, essential prerequisites concerning data quality, including harmonization and standardization, and future perspectives of the indirect determination of reference intervals using routine laboratory data.
Clinical Chemistry and Laboratory Medicine, Sep 15, 2018
Background: External quality assessment (EQA) programs for general chemistry tests have evolved f... more Background: External quality assessment (EQA) programs for general chemistry tests have evolved from between laboratory comparison programs to trueness verification surveys. In the Netherlands, the implementation of such programs has reduced inter-laboratory variation for electrolytes, substrates and enzymes. This allows for national and metrological traceable reference intervals, but these are still lacking. We have initiated a national endeavor named NUMBER (Nederlandse UniforMe Beslisgrenzen En Referentie-intervallen) to set up a sustainable system for the determination of standardized reference intervals in the Netherlands. Methods: We used an evidence-based 'big-data' approach to deduce reference intervals using millions of test results from patients visiting general practitioners from clinical laboratory databases. We selected 21 medical tests which are either traceable to SI or have Joint Committee for Traceability in Laboratory Medicine (JCTLM)-listed reference materials and/or reference methods. Per laboratory, per test, outliers were excluded, data were transformed to a normal distribution (if necessary), and means and standard deviations (SDs) were calculated. Then, average means and SDs per test were calculated to generate pooled (mean ± 2 SD) reference intervals. Results were discussed in expert meetings. Results: Sixteen carefully selected clinical laboratories across the country provided anonymous test results (n = 7,574,327). During three expert meetings, participants found consensus about calculated reference intervals for 18 tests and necessary partitioning in subcategories, based on sex, age, matrix and/or method. For two tests further evaluation of the reference interval and the study population were considered necessary. For glucose, the working group advised to adopt the clinical decision limit. Conclusions: Using a 'big-data' approach we were able to determine traceable reference intervals for 18 general chemistry tests. Nationwide implementation of these established reference intervals has the potential to improve unequivocal interpretation of test results, thereby reducing patient harm.
Journal of Proteome Research, Jan 6, 2015
Clinically actionable quantification of protein biomarkers by mass spectrometry (MS) requires ana... more Clinically actionable quantification of protein biomarkers by mass spectrometry (MS) requires analytical performance in concordance with quality specifications for diagnostic tests. Laboratory-developed tests should, therefore, be validated in accordance with EN ISO 15189:2012 guidelines for medical laboratories to demonstrate competence and traceability along the entire workflow, including the selected standardization strategy and the phases before, during, and after proteolysis. In this study, bias and imprecision of a previously developed MS method for quantification of serum apolipoproteins A-I (Apo A-I) and B (Apo B) were thoroughly validated according to Clinical and Laboratory Standards Institute (CLSI) guidelines EP15-A2 and EP09-A3, using 100 patient sera and either stable-isotope labeled (SIL) peptides or SIL-Apo A-I as internal standard. The systematic overview of error components assigned sample preparation before the first 4 h of proteolysis as major source (∼85%) of within-sample imprecision without external calibration. No improvement in imprecision was observed with the use of SIL-Apo A-I instead of SIL-peptides. On the contrary, when the use of SIL-Apo A-I was combined with external calibration, imprecision improved significantly (from ∼9% to ∼6%) as a result of the normalization for matrix effects on linearity. A between-sample validation of bias in 100 patient sera further supported the presence of matrix effects on digestion completeness and additionally demonstrated specimen-specific biases associated with modified peptide sequences or alterations in protease activity. In conclusion, the presented overview of bias and imprecision components contributes to a better understanding of the sources of errors in MSbased protein quantification and provides valuable recommendations to assess and control analytical quality in concordance with the requirements for clinical use.
Advances in laboratory medicine, Oct 30, 2020
Clinical Epidemiology, Jul 1, 2019
Purpose: Apolipoproteins C-I, C-II, C-III and E have been associated with risk of arterial thromb... more Purpose: Apolipoproteins C-I, C-II, C-III and E have been associated with risk of arterial thrombotic diseases. We investigated whether these apolipoproteins have prothrombotic properties and are associated with risk of venous thromboembolism (VTE). Patients and methods: A total of 127 VTE patients and 299 controls were randomly selected from the Multiple Environmental and Genetic Assessment of Risk Factors for Venous Thrombosis study (1999-2004), in the Netherlands. The apolipoproteins were quantified using mass spectrometry (LC/MS/MS), and their levels were analyzed as continuous variable (per SD increase). Results: In controls, increases in levels of apolipoproteins were associated with increases in levels of vitamin K-dependent factors, factor XI, antithrombin and clot lysis time. Additionally, increasing apolipoproteins C-III and E levels were associated with higher factor VIII and von Willebrand factor levels. Levels of C-reactive protein were not associated with any apolipoprotein. The age-and sex-adjusted odds ratios of apolipoproteins E, C-III, CII and CI to the risk of venous thrombosis were 1.21 (95% CI, 0.98-1.49), 1.19 (95% CI, 0.99-1.44), 1.24 (95% CI, 0.95-1.61) and 1.06 (95% CI, 0.87-1.30) per SD increase, respectively. These odds ratios did not attenuate after adjustments for statin use, estrogen use, BMI, alcohol use, and self-reported diabetes. Conclusions: Levels of apolipoproteins C-I, C-II, C-III and E are associated with those of several coagulation factors. However, whether these apolipoproteins are also associated with an increased risk of VTE remains to be established.
Journal of Clinical Epidemiology, Sep 1, 1997
Strum lipoprotein(a) (Lp( a)) and its correlates were studied in African Aboriginal Pygmies (n = ... more Strum lipoprotein(a) (Lp( a)) and its correlates were studied in African Aboriginal Pygmies (n = 146) and Bantus (n = 208) f rom 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 Pyg mies 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) 1 evels 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 high er in Pygmy and Bantu males, and 2.9-to 3.6-fold higher in Pygmy and Bantu females (e 5 0.05). A cross the population samples studied ethnicity predicted 12% and 17% of serum Lp(a) variance in males and females, respectively.
Annals of Clinical Biochemistry, Mar 19, 2019
An elevated low-density lipoprotein cholesterol concentration is a classical risk factor for card... more An elevated low-density lipoprotein cholesterol concentration is a classical risk factor for cardiovascular disease. This has led to pharmacotherapy in patients with atherosclerotic heart disease or high heart disease risk with statins to reduce serum low-density lipoprotein cholesterol. Even in patients in whom the target levels of low-density lipoprotein cholesterol are reached, there remains a significant residual cardiovascular risk; this is due, in part, to a focus on low-density lipoprotein cholesterol alone and neglect of other important aspects of lipoprotein metabolism. A more refined lipoprotein analysis will provide additional information on the accumulation of very low-density lipoproteins, intermediate density lipoproteins, chylomicrons, chylomicron-remnants and Lp(a) concentrations. Instead of measuring the cholesterol and triglyceride content of the lipoproteins, measurement of their apolipoproteins (apos) is more informative. Apos are either specific for a particular lipoprotein or for a group of lipoproteins. In particular measurement of apos in atherogenic particles is more biologically meaningful than the measurement of the cholesterol concentration contained in these particles. Applying apo profiling will not only improve characterization of the lipoprotein abnormality, but will also improve definition of therapeutic targets. Apo profiling aligns with the concept of precision medicine by which an individual patient is not treated as 'average' patient by the average (dose of) therapy. This concept of precision medicine fits the unmet clinical need for stratified cardiovascular medicine. The requirements for clinical application of proteomics, including apo profiling, can now be met using robust mass spectrometry technology which offers desirable analytical performance and standardization.
Clinical Chemistry, Sep 1, 2002
The Dutch project "Calibration 2000" aims at harmonization of laboratory results via calibration ... more The Dutch project "Calibration 2000" aims at harmonization of laboratory results via calibration by development of matrix-based secondary reference materials. We considered the selection, preparation, and characterization of 34 potential reference materials (PRMs). Methods: Sixteen PRMs were prepared either strictly according to the NCCLS C37-A protocol or in a less stringent and more convenient way. In addition, 18 commercial, so-called human serum-based calibrators or controls were purchased and tested. Lipoprotein integrity was evaluated by examining the physicochemical characteristics of the materials. Commutability of the PRMs was assessed in 86 Dutch clinical laboratories, using a multicenter split-patient-sample between-fieldmethod (twin-study) design. Normalized residuals of the PRMs with respect to the patient regression lines were calculated; in addition, the extra contribution of each PRM to the total measurement uncertainty (CV Netto ) was calculated. On the basis of these results, the most native PRM was selected to investigate its potential to reduce interlaboratory variation and to improve lipid and apolipoprotein standardization. Results: In general, only the NCCLS C37-A-type materials displayed normalized residuals below the decision limit for commutability and had small CV Netto values ranging between 0 and 3.8%. This contrasts with the findings in regularly pooled frozen sera and lyophilized cryoprotected PRMs. In two subsequent external quality assessment surveys, the NCCLS type C37-A materials contributed to reducing the intermethod lipid and (apo)lipoprotein variation to ϳ2-4%. Conclusions: NCCLS C37-A materials have a strong potential as secondary reference materials, not only for cholesterol but also for HDL-cholesterol, LDL-cholesterol, triglyceride, and apolipoprotein measurements.
Clinical Chemistry and Laboratory Medicine, Jan 17, 2018
Calibration 2.000 was initiated 20 years ago for standardization and harmonization of medical tes... more Calibration 2.000 was initiated 20 years ago for standardization and harmonization of medical tests. The program also intended to evaluate adequate implementation of the In Vitro Diagnostics (IVD) 98/79/EC directive, in order to ensure that medical tests are fit-for-clinical purpose. The Calibration 2.000 initiative led to ongoing verification of test standardization and harmonization in the Netherlands using commutable external quality assessment (EQA)-tools and a type 1 EQA-design, where feasible. National support was guaranteed by involving all laboratory professionals as well as laboratory technicians responsible for EQA and quality officers. A category 1 EQA-system for general chemistry analytes, harmonizers for specific analytes like hGH and IGF-1, and commutable materials for other EQA-sections have been developed and structurally introduced in the EQA-schemes. The type 1 EQA-design facilitates the dialogue between individual specialists in laboratory medicine and the IVD-industry to reduce lot-to-lot variation and to improve standardization. In such a way, Calibration 2.000 sheds light on the metrological traceability challenges that we are facing and helps the laboratory community to get the issues on the table and resolved. The need for commutable trueness verifiers and/or harmonizers for other medical tests is now seen as paramount. Much knowledge is present in the Netherlands and for general chemistry, humoral immunology and protein chemistry, a few endocrinology tests, and various therapeutic drug monitoring (TDM) tests, commutable materials are available. Also the multi sample evaluation scoring system (MUSE) and the category 1 EQA-design offer many possibilities for permanent education of laboratory professionals to further improve the between and within laboratory variation and the test equivalence.
Clinica Chimica Acta, Jun 1, 2019
alert clinicians when the 80% decrease was reached, with the hope of improving request appropriat... more alert clinicians when the 80% decrease was reached, with the hope of improving request appropriateness. Since October 2017, a comment indicating "a decrease ε80% from peak value" was added, whenever relevant, to PCT reports of ICU patients as a clinical validation rule. The number of PCT requests was audited from January to September 2018 (P2) and compared with the same period of 2017 (P1), before the rule implementation. 1103 PCT determinations for 181 ICU patients (mean, 6.1 tests per patient; range 1-60) and 991 PCT determinations for 185 patients (mean, 5.4 tests per patient; range 1-38) were ordered during P1 and P2, respectively. During P2, 258 comments were added to PCT reports of 47 patients (mean, 5.5 comments per patient; range 1-25). This resulted in a 10% decrease in total PCT requests and an average reduction of 0.7 in requests per patient. This corresponded to a yearly saving of ~6,000 €. The post-analytical phase is the most overlooked phase of the total examination process. However, its proper management is crucial for patient safety and clinical governance of laboratory tasks, including appropriate test utilization. We showed that adding a standard comment to the PCT report for highlighting the clinical information given by the biomarker behaviour in ICU patients undergoing antibiotics can increase the appropriateness for this critical, expensive and often misused test.
Methods, Jun 1, 2015
Objectives: The 2010 Society of Gynecologic Oncologists (SGO) Practice Survey revealed that up to... more Objectives: The 2010 Society of Gynecologic Oncologists (SGO) Practice Survey revealed that up to one third of operations performed by gynecologic oncologists are for benign indications. This evolving practice pattern may have significant workforce implications and is a topic not well studied. The aim of this study was to characterize the benign gynecologic surgical practices of SGO members and identify attitudes toward noncancer gynecologic surgery. Methods: In November 2013, SGO members were invited to complete a 23-question online survey regarding surgical practice patterns. Descriptive statistics were used to analyze responses as well as chi square and t-test banalyses. Results: Responses were received from 234 of 1154 SGO members (20%). Overall, respondents reported that 50% of patients were referred with known malignant disease, 30% with suspected malignant disease, and 20% with known benign disease. Minimally invasive surgery (MIS) was used in 66% of overall surgical volume but 78% of benign surgeries (P = b0.0001). The most common noncancer referrals were: adnexal masses without features concerning for malignancy, benign vulvar disease, and patients with medical comorbidities. More than half of respondents (65%) reported increased frequency of benign surgical referrals due to ability to offer MIS. Most (67%) felt benign surgery to have neutral or no impact on their ability to care for women with cancer. Gynecologic oncologists in private practice were more likely to report that benign gynecology positively affected their practice's finances than academic clinicians (61% versus 39%, P = 0.004). These clinicians were also more likely to encourage referral of patients with benign disease (45% versus 29%, P = 0.027). Conclusions: Benign gynecologic surgery accounts for approximately 20% of gynecologic oncologists' surgical volume. Most gynecologic oncologists have a neutral view on the impact of benign gynecologic surgery on their ability to care for cancer patients, professional satisfaction, and practice finances. Subspecialty expertise in minimally invasive techniques is likely to foster continued referrals for benign surgical procedures and management of benign pelvic masses.
Nederland is anno 2004 in SKMLverband geëvalueerd. De analytische kwaliteit werd getest met commu... more Nederland is anno 2004 in SKMLverband geëvalueerd. De analytische kwaliteit werd getest met commuteerbare kwaliteitscontrolematerialen waaraan referentiewaarden zijn toegekend. Op 150 deelnemende klinisch-chemische laboratoria voeren 22 laboratoria routinematig apo-A-I-en -B-bepalingen uit. Gepoolde data uit zes tweemaandelijkse rondzendingen tonen aan dat de gemiddelde binnenlabprecisie voor apo B en apo A-I 4,5% respectievelijk 4,0% bedraagt. De gemiddelde absolute bias voor apo B en apo A-I is 6,8% respectievelijk 8,6%. De gemiddelde interlaboratoriumvariatie voor apo B en apo A-I bedraagt 8,6% respectievelijk 9,9%. Eén jaar na IVD-98/79/EC-implementatie, blijkt de gemiddelde binnenlabprecisie en bias voor de apo-A-I-en -B-bepalingen niet te voldoen aan de gewenste kwaliteit afgeleid uit biologische variatiegegevens. Ondanks de beschikbaarheid van internationaal erkende referentiesystemen en wettelijke kaders is er ruimte voor verdere verbetering van de apo-A-I-en -B-standaardisatie.
Clinical Chemistry and Laboratory Medicine, 2017
Background: To provide its participants with an external quality assessment system (EQAS) that ca... more Background: To provide its participants with an external quality assessment system (EQAS) that can be used to check trueness, the Dutch EQAS organizer, Organization for Quality Assessment of Laboratory Diagnostics (SKML), has innovated its general chemistry scheme over the last decade by introducing fresh frozen commutable samples whose values were assigned by Joint Committee for Traceability in Laboratory Medicine (JCTLM)-listed reference laboratories using reference methods where possible. Here we present some important innovations in our feedback reports that allow participants to judge whether their trueness and imprecision meet predefined analytical performance specifications. Methods: Sigma metrics are used to calculate performance indicators named 'sigma values'. Tolerance intervals are based on both Total Error allowable (TEa) according to biological variation data and state of the art (SA) in line with the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) Milan consensus. Results: The existing SKML feedback reports that express trueness as the agreement between the regression line through the results of the last 12 months and the values obtained from reference laboratories and calculate imprecision from the residuals of the regression line are now enriched with sigma values calculated from the degree to which the combination of trueness and imprecision are within tolerance limits. The information and its conclusion to a simple two-point scoring system are also graphically represented in addition to the existing difference plot. Conclusions: By adding sigma metrics-based performance evaluation in relation to both TEa and SA tolerance intervals to its EQAS schemes, SKML provides its participants with a powerful and actionable check on accuracy.
Clinical Chemistry and Laboratory Medicine, 2008
In last three decades, as requirement increases with availability of newer technology, automated ... more In last three decades, as requirement increases with availability of newer technology, automated equipments took over manual and semi-automatic analysis of patients samples. This trend was observed most profoundly at tertiary care hospitals, where faster turnaround time is a patient care necessity. These automation, nonetheless, also provided better reproducibility, precision and accuracy of results; in addition to 24/7 availability of major lab testing panels. In this regard, the present study described the comparative equipment performance evaluation of conventional chemistry analyzer, Hirachi 912 with modular Cobas 6000 (c 501). Blood samples from patients of either gender, n = 70 (Males = 58, female = 42) were collected during Dec 2011 to Dec 2012 for test panel of Urea, Creatinine, ALT, uric acid, sugar and cholesterol. Standard methodologies and principles were used to analyze all parameters on both instruments. Data were compared using regression analysis and statistical significance of P< 0.05. Comparative analysis showed excellent data correlations among all six parameters on both instruments with R regression ranging from 0.8435 to 0.998, depicting the precision 2 and reliability of methods, standardization and system equivalency. Correlation results showed regression R for urea as R 0.9678, Creatinine R 0.8435, ALT R 0.9955, uric acid R 0.993; sugar R 0.9988 and cholesterol 2 2 2 2 2 2 R 0.9952. In conclusion, regression analysis exhibited near-equivalent data representation ranging from 84.3% 2 to 99.8% of both instruments, thus depicting that both are standardized and properly calibrated to be used simultaneously and inter-changeable for routine chemistry analysis of referred parameters.
Clinical Chemistry and Laboratory Medicine, 1995
The analytical performance of a direct, immunoseparation based LDL-cholesterol method (Genzyme Co... more 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 χ -0.107; Ν = 45). In contrast, immunoseparation based LDL-cholesterol (y) differed significantly from polyvinyl sulphate LDL-cholesterol (x) results (y = 0.922 χ + 0.234; Ν = 103). Freezing normotriacylglycerolaemic sera (three weeks, -20 °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/1 serum triacylglycerols. We conclude that the immunoseparation based LDL-cholesterol method is a practical, not technically demanding technique well applicable within routine clinical laboratories. The method shows a markedly improved analytical precision in comparison to current routine methods, and hence has potential to decrease total test imprecision. The immunoseparation based LDL-cholesterol method produces results identical to those obtained by Friedewald in healthy blood donors, and above all overcomes a major pitfall of the Friedewald equation enabling LDL-cholesterol measurements in hypertriacylglycerolaemic sera. Its acceptance should improve the reliability of LDL-cholesterol testing and improve clinical decision making.
PLOS ONE
The aim of this study was to determine reference intervals in an outpatient population from Vall ... more The aim of this study was to determine reference intervals in an outpatient population from Vall d’Hebron laboratory using an indirect approach previously described in a Dutch population (NUMBER project). We used anonymized test results from individuals visiting general practitioners and analysed during 2018. Analytical quality was assured by EQA performance, daily average monitoring and by assessing longitudinal accuracy between 2018 and 2020 (using trueness verifiers from Dutch EQA). Per test, outliers by biochemically related tests were excluded, data were transformed to a normal distribution (if necessary) and means and standard deviations were calculated, stratified by age and sex. In addition, the reference limit estimator method was also used to calculate reference intervals using the same dataset. Finally, for standardized tests reference intervals obtained were compared with the published NUMBER results. Reference intervals were calculated using data from 509,408 clinical r...
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Papers by Christa Cobbaert