Publications by authors named "Sofie Schouwers"

16 Publications

  • Page 1 of 1

Serological response in health care workers after a single dose of SARS-CoV-2 vaccine using six automated SARS-CoV-2 antibody assays.

Diagn Microbiol Infect Dis 2021 Oct 10;101(2):115486. Epub 2021 Jul 10.

University Hospital Antwerp, Laboratory Medicine, Edegem, Belgium. Electronic address:

Spike (S)- and nucleocapsid (N)-specific serological assay responses were determined before and/or after first dose SARS-CoV-2 vaccination in 22 individuals. S-specific assays quantified antibodies after vaccination with significant higher levels in participants with a previous infection. Be cautious combining N-/S-specific assay results, potentially differentiating post-infection/vaccination immunization as assay-specific N-antibody waning was observed.
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http://dx.doi.org/10.1016/j.diagmicrobio.2021.115486DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8272050PMC
October 2021

Current laboratory and clinical practices in reporting and interpreting anti-nuclear antibody indirect immunofluorescence (ANA IIF) patterns: results of an international survey.

Auto Immun Highlights 2020 Nov 23;11(1):17. Epub 2020 Nov 23.

Department of Microbiology and Immunology, KU Leuven, Leuven, Belgium.

Background: The International Consensus on Antinuclear Antibody (ANA) Patterns (ICAP) has recently proposed nomenclature in order to harmonize ANA indirect immunofluorescence (IIF) pattern reporting. ICAP distinguishes competent-level from expert-level patterns. A survey was organized to evaluate reporting, familiarity, and considered clinical value of ANA IIF patterns.

Methods: Two surveys were distributed by European Autoimmunity Standardization Initiative (EASI) working groups, the International Consensus on ANA Patterns (ICAP) and UK NEQAS to laboratory professionals and clinicians.

Results: 438 laboratory professionals and 248 clinicians from 67 countries responded. Except for dense fine speckled (DFS), the nuclear competent patterns were reported by > 85% of the laboratories. Except for rods and rings, the cytoplasmic competent patterns were reported by > 72% of laboratories. Cytoplasmic IIF staining was considered ANA positive by 55% of clinicians and 62% of laboratory professionals, with geographical and expertise-related differences. Quantification of fluorescence intensity was considered clinically relevant for nuclear patterns, but less so for cytoplasmic and mitotic patterns. Combining IIF with specific extractable nuclear antigens (ENA)/dsDNA antibody testing was considered most informative. Of the nuclear competent patterns, the centromere and homogeneous pattern obtained the highest scores for clinical relevance and the DFS pattern the lowest. Of the cytoplasmic patterns, the reticular/mitochondria-like pattern obtained the highest scores for clinical relevance and the polar/Golgi-like and rods and rings patterns the lowest.

Conclusion: This survey confirms that the major nuclear and cytoplasmic ANA IIF patterns are considered clinically important. There is no unanimity on classifying DFS, rods and rings and polar/Golgi-like as a competent pattern and on reporting cytoplasmic patterns as ANA IIF positive.
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http://dx.doi.org/10.1186/s13317-020-00139-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7684889PMC
November 2020

Harmonizing by reducing inter-run variability: performance evaluation of a quality assurance program for antinuclear antibody detection by indirect immunofluorescence.

Clin Chem Lab Med 2019 06;57(7):990-998

Department of Laboratory Medicine, OLV Hospital Aalst, Moorselbaan 164, 9300 Aalst, Belgium, Phone: +32 (0)53/72 42 91, Fax: +32 (0)53/72 45 88.

Background The introduction of automated anti-nuclear antibody (ANA) indirect immunofluorescence (IIF) analysis may allow for more harmonized ANA IIF reporting, provided that a thorough quality assurance program controls this process. The aim of this study was to evaluate various quality indicators used for ANA IIF analysis with the final goal of optimizing the iQC program. Methods In an experimental setup, we introduced artificial errors, mimicking plausible problems during routine practice on a QUANTA-Lyser-NOVA View® system (Inova Diagnostics, San Diego, CA, USA). Predetermined quality indicators were evaluated against predefined acceptance criteria. In addition, we retrospectively investigated the applicability of the selected quality indicators in the daily routine practice during three pre-defined periods. Results Both the experimental as the retrospective study revealed that pre-analytical, analytical and post-analytical errors were not highlighted by company internal quality control (iQC) materials. The use of patient derived iQC samples, median fluorescence intensity results per run and the percentage of positive ANA IIF results as additional quality indicators ensured a more adequate ANA IIF quality assurance. Furthermore, negative and moderate positive sample iQC materials merit clinical validation, as titer changes of >1 correspond to clinically important shifts. Traditional Westgard rules, including a clinically defined stop limit, revealed to be useful in monitoring of the supplemental quality indicators. Conclusions A thorough ANA IIF quality assurance for daily routine practice necessitates the addition of supplemental quality indicators in combination with well-defined acceptance criteria.
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http://dx.doi.org/10.1515/cclm-2018-0933DOI Listing
June 2019

Variation in antinuclear antibody detection by automated indirect immunofluorescence analysis.

Ann Rheum Dis 2019 06 20;78(6):e48. Epub 2018 Apr 20.

Department of Laboratory Medicine, University Hospital Leuven, Leuven, Belgium.

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http://dx.doi.org/10.1136/annrheumdis-2018-213543DOI Listing
June 2019

The importance of detecting anti-DFS70 in routine clinical practice: comparison of different care settings.

Clin Chem Lab Med 2018 06;56(7):1090-1099

Department of Laboratory Medicine, OLV Hospital, Aalst, Belgium.

Background: Screening for antinuclear antibodies by indirect immunofluorescence (ANA-IIF) is essential in the diagnostic workup of ANA-associated autoimmune rheumatic diseases (AARDs). However, also healthy individuals may test positive, making the interpretation challenging. Recent reports suggest that dense fine speckled 70 antibodies (anti-DFS70) may facilitate this challenge. Here, we investigate their clinical importance based on data from four Belgian laboratories (one primary, two secondary and one tertiary care).

Methods: At least one specific DFS70 assay (DFS70 IgG ELISA or lineblot [Euroimmun, full length antigen] and/or DFS70 IgG CLIA [Inova Diagnostics, truncated antigen]) was performed on four consecutive cohorts of homogeneous-like ANA-IIF samples (n=697). Co-occurrence with AARD-specific ANA and clinical information were documented in the anti-DFS70-positive samples.

Results: Using a combination of solid phase techniques, we found between 7.6% and 26% anti-DFS70 in the different cohorts. Focusing on anti-DFS70 CLIA-positive samples without co-occurrence of AARD-specific ANA, we observed a trend towards lower frequency in tertiary (8% [p=0.0786]) and secondary care (12% [p=0.1275] and 6% [p<0.001]) compared to primary care (21%). Moreover, in this specific subpopulation, AARD was less frequent (0%-50% compared to 6%-77% in the total anti-DFS70-positive group).

Conclusions: Anti-DFS70 prevalence depends on the applied assay and care setting. Our data suggest that, for an ANA-IIF-positive patient, it is rather the absence of AARD-associated ANA and clinical symptoms that contribute to the exclusion of AARD than the presence of anti-DFS70. Nevertheless, isolated anti-DFS70 helps to clarify positive ANA-IIF results, especially if pretest probability for AARD is low.
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http://dx.doi.org/10.1515/cclm-2017-0541DOI Listing
June 2018

ANA IIF Automation: Moving towards Harmonization? Results of a Multicenter Study.

J Immunol Res 2017 21;2017:6038137. Epub 2017 Feb 21.

Department of Laboratory Medicine, OLV Hospital, Aalst, Belgium.

. Our study aimed to investigate whether the introduction of automated anti-nuclear antibody (ANA) indirect immunofluorescence (IIF) analysis decreases the interlaboratory variability of ANA titer results. . Three serum samples were sent to 10 laboratories using the QUANTA-Lyser® in combination with the NOVA View®. Each laboratory performed the ANA IIF analysis 10x in 1 run and 1x in 10 different runs and determined the endpoint titer by dilution. One of the three samples had been sent in 2012, before the era of ANA IIF automation, by the Belgian National External Quality Assessment (EQA) Scheme. Harmonization was evaluated in terms of variability in fluorescence intensity (LIU) and ANA IIF titer. . The evaluation of the intra- and interrun LIU variability revealed a larger variability for 2 laboratories, due to preanalytical and analytical problems. Reanalysis of the EQA sample resulted in a lower titer variability. Diluted endpoint titers were similar to the estimated single well titer and the overall median titer as reported by the EQA in 2012. The introduction of automated microscopic analysis allows more harmonized ANA IIF reporting, provided that this totally automated process is controlled by a thorough quality assurance program, covering the total ANA IIF process.
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http://dx.doi.org/10.1155/2017/6038137DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5339452PMC
April 2017

Biological Variation of Chloride and Sodium in Sweat Obtained by Pilocarpine Iontophoresis in Adults: How Sure are You About Sweat Test Results?

Lung 2017 04 27;195(2):241-246. Epub 2017 Feb 27.

Department of Laboratory Medicine, GZA Hospitals, Wilrijk, Belgium.

Introduction: The measurement of chloride and sodium concentrations in sweat is an important test for the diagnosis of cystic fibrosis (CF). The aim of this study was to assess the analytical variation (CV) and within-subject (CV) and between-subject (CV) biological variation of chloride and sodium concentrations in sweat, collected by pilocarpine iontophoresis and to determine their effect on the clinical interpretation of sweat test results.

Methods: Twelve Caucasian adults (six male and six female) without symptoms suggestive for CF and with a mean age of 41 years (range 28-59) were included in the study. At least eight samples of sweat were collected from each individual by pilocarpine iontophoresis. Chloride and sodium concentrations were measured in duplicate for each sample using ion selective electrodes. After the removal of outliers, the CV, CV, and CV of chloride and sodium were determined, and their impact on measurement uncertainty and reference change value were calculated.

Results: The CV, CV, and CV of chloride in sweat samples were 6.5, 17.7, and 47.2%, respectively. The CV, CV, and CV of sodium sweat samples were 6.0, 17.5, and 42.6%, respectively.

Conclusion: Our study indicates that sweat chloride and sodium concentration results must be interpreted with great care. Different components of variation, particularly the biological variations, have a considerable impact on the interpretation of these results. If no pre-analytical, analytical, or post-analytical errors are suspected, repeated sweat testing to confirm first-measurement results might not be desirable.
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http://dx.doi.org/10.1007/s00408-017-9984-6DOI Listing
April 2017

Near-fatal persistent anion- and osmolal-gap acidosis due to massive gamma-butyrolactone/ethanol intoxication.

Ann Clin Biochem 2015 Mar 9;52(Pt 2):283-7. Epub 2014 Sep 9.

Toxicological Center, University of Antwerp, Antwerp, Belgium.

We report a case of an ethanol and massive gamma-butyrolactone (GBL) intoxication, the precursor of the recreational drug gamma-hydroxybutyric acid (GHB), resulting in life-threatening metabolic acidosis (pH 6.5) with a highly increased anion- and osmolal gap. Rapid analysis using gas chromatography revealed a GHB plasma concentration of 4400 mg/L, far above the upper limit concentration of 1000 mg/L found in adult fatalities attributed to GBL. Full recovery was established following supportive treatment including haemodialysis. This is the first report of a combined ethanol/GBL intoxication as a cause of high serum anion- and osmolal-gap metabolic acidosis.
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http://dx.doi.org/10.1177/0004563214553278DOI Listing
March 2015

Value-added reporting of antinuclear antibody testing by automated indirect immunofluorescence analysis.

Clin Chem Lab Med 2014 Apr;52(4):547-51

Background: Automated systems for antinuclear antibody analysis are being introduced. The aim was to evaluate whether automated quantitative reading of fluorescence intensity is clinically relevant and allows for value-added reporting of test results.

Methods: Consecutive samples (n=260) were used to correlate fluorescence intensity with end-point titer. Moreover, 434 samples from controls (150 healthy blood donors, 150 chronic fatigue syndrome, and 134 diseased controls) and 252 samples (obtained at diagnosis) from patients with systemic rheumatic diseases were screened for antinuclear antibodies (1:80) on HEp-2 cells using NOVA View, and likelihood ratios were calculated for fluorescence intensity result intervals.

Results: There was a significant correlation between end-point titer and fluorescence intensity. Likelihood ratios for a systemic rheumatic disease increased with increasing fluorescence intensity. The likelihood ratio for a systemic rheumatic disease was 0.06, 0.18, 0.51, 5.3, and 37.5 for a fluorescence intensity of ≤66, 67-150, 151-300, 301-1000, >1000, respectively. A range of 31%-37% of the patients with Sjögren's syndrome, systemic sclerosis or systemic lupus erythematosus had fluorescence intensities >1000.

Conclusions: Estimation of fluorescence intensity by automated antinuclear antibody analysis offers clinically useful information. Likelihood ratios based on fluorescence intensity test result intervals aid with the interpretation of automated antinuclear antibody analysis and allow value-added reporting.
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http://dx.doi.org/10.1515/cclm-2013-0610DOI Listing
April 2014

Influence of separator gel in Sarstedt S-Monovette® serum tubes on various therapeutic drugs, hormones, and proteins.

Clin Chim Acta 2012 Jan 14;413(1-2):100-4. Epub 2011 Sep 14.

Laboratory for Clinical Chemistry and Toxicology, ZNA Stuivenberg, Antwerp, Belgium.

Background: A separator or barrier gel is a common component of serum and plasma collection tubes. Despite their advantages, the use of these tubes is not universally accepted, especially for therapeutic drug monitoring (TDM). The aim of this study was to evaluate whether the polyacrylester separator gel in Sarstedt S-Monovette\® tubes influences the concentration of 10 selected parameters (amikacin, vancomycin, valproic acid, acetaminophen, cortisol, free thyroxine, thyroid-stimulating hormone, transferrin, prealbumin and carcinoembryonic antigen) in a clinically significant way.

Methods: Results from patient samples collected in plastic Sarstedt S-Monovette® tubes with separator gel were compared with those from plain serum sample tubes. Analytes were measured in both tubes on 4 consecutive days to study the influence of prolonged contact with the separator gel. Between analyses tubes were stored at 4°C. Stability was also evaluated over 72 h for each collection tube. When statistical differences were detected, the clinical significance was evaluated based on the total allowable error (TEa).

Results: On day 1 no statistically significant differences were observed between samples collected in Sarstedt S-Monovette® tubes with and without separator gel. Statistical differences were present from day 2 on, but were not clinically significant. All evaluated parameters were clinically stable over 72 h at 4°C based on TEa, except for transferrin en fT4.

Conclusion: The separator gel in Sarstedt S-Monovette® tubes did not show statistically significant differences on the day of phlebotomy. Later on statistically significant differences appeared but except for the stability of fT4 and transferrin they all remained clinically insignificant.
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http://dx.doi.org/10.1016/j.cca.2011.08.037DOI Listing
January 2012

Evaluation of a new set of automated chemiluminescense assays for anticardiolipin and anti-beta2-glycoprotein I antibodies in the laboratory diagnosis of the antiphospholipid syndrome.

Thromb Res 2011 Dec 6;128(6):565-9. Epub 2011 May 6.

Coagulation Laboratory, Department of Clinical Chemistry, Microbiology and Immunology, Ghent University Hospital, Ghent, Belgium.

Introduction: The laboratory diagnosis of antiphospholipid syndrome (APS) requires the demonstration of antiphospholipid antibodies (aPL): lupus anticoagulant (LAC) measured through coagulation assays, anticardiolipin IgG or IgM antibodies (aCL) and/or anti-β2glycoprotein I IgG or IgM antibodies (aβ2GPI), usually detected by ELISA.

Materials And Methods: We evaluated the diagnostic value of aCL and aβ2GPI measured by a new automated system using the chemiluminescence principle, the immunoanalyzer Zenit RA (Menarini).

Results: Results of aCL and aβ2GPI were correlated with the clinical background of the patients and with results of ELISA (n=314). Correlated to the clinical background sensitivity/specificity ranged for aCL IgG between 7.5-45.2% / 54.2-98.8%, for aCL IgM 3.4-5.5% / 89.9-94%, for aβ2GPI IgG 5.5-25.3% / 75.6-100% and aβ2GPI IgM 3.4-4.8% / 89.9-92.3%, depending on the cut-off used. Sensitivity with manufacturer's cut-offs was comparable to ELISA, except for aβ2GPI IgG with a significantly lower sensitivity compared to ELISA (5.5% vs 11.6%). In the APS patient population (n=30) sensitivity of aCL IgG and aβ2GPI IgG was higher measured by ELISA compared to Zenit RA (46.7% vs 30.0%, and 46.7% vs 26.7%, respectively). Agreement between Zenit RA results and ELISA results for the four parameters was moderate (Kappa-values ranging 0.509-0.565). Sensitivity was 38.5%, 53.3%, 40% and 69.2% for aCL IgG, aCL IgM, aβ2GPI IgG and aβ2GPI IgM, respectively, applying the highest cut-off value for Zenit RA, raising towards 64.3%, 100%, 57.1%, for aCL IgG, aCL IgM, aβ2GPI IgG, respectively, in a APS patient population.

Conclusions: The new technology of chemiluminescense for measuring aPL showed good performance characteristics. Interpretation of results with a cut-off value associated with a good discrimination for disease, resulted in a lower sensitivity for the diagnosis of APS for aβ2GPI IgG measured by Zenit RA assays compared to ELISA; sensitivity for aCL IgG was comparable to ELISA. Specificity for all parameters was high and comparable for aCL and aβ2GPI.
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http://dx.doi.org/10.1016/j.thromres.2011.04.004DOI Listing
December 2011

Sample evaporation from pierceable cups: still an important source of analytical error.

Clin Biochem 2010 Dec 17;43(18):1464-7. Epub 2010 Sep 17.

Laboratory for Clinical Chemistry and Toxicology, ZNA Stuivenberg, Antwerp, Belgium.

Background: We illustrate the impact of sample evaporation on analytical results in laboratory practice and highlight preventive measures.

Methods: Plasma (n=10) was analysed for glucose, Na(+), HCO(3)(-) and calcium on six different sample configurations at 5 time points within 2h.

Results: With time glucose, Na(+) and calcium values increased and HCO(3)(-) values decreased in a clinically significant way.

Conclusions: Analytical error due to evaporation may be significant, but can be reduced with optimal sample handling. A pierceable cover does not prevent loss of HCO(3)(-).
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http://dx.doi.org/10.1016/j.clinbiochem.2010.09.004DOI Listing
December 2010
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