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Clinical Chemistry and Laboratory Medicine (CCLM)

Published in Association with the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM)

Editor-in-Chief: Plebani, Mario

Ed. by Gillery, Philippe / Lackner, Karl J. / Lippi, Giuseppe / Melichar, Bohuslav / Payne, Deborah A. / Schlattmann, Peter / Tate, Jillian R.

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Calcium pyrophosphate and monosodium urate crystals in synovial fluid as a cause of pseudoeosinophilia

1 / Manfred Neubauer1 / Franz Quehenberger2 / Mariana Stettin1 / Franz Rainer1

1Department of Internal Medicine, Hospital Barmherzige Brueder Graz-Eggenberg, Graz, Austria

2Institute of Medical Informatics, Statistics and Documentation, Medical University of Graz, Austria

Corresponding author: Christoph Robier, Central Laboratory, Department of Internal Medicine, Hospital Barmherzige Brueder, Graz-Eggenberg, Bergstrasse 27, 8020 Graz, Austria Phone: +43-316-5989-6671

Citation Information: Clinical Chemistry and Laboratory Medicine. Volume 49, Issue 8, Pages 1345–1347, ISSN (Online) 1437-4331, ISSN (Print) 1434-6621, DOI: 10.1515/CCLM.2011.212, May 2011

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This article offers supplementary material which is provided at the end of the article.


Background: Synovial fluid (SF) leukocytes can be counted microscopically in a Neubauer chamber or by automated procedures using haematology analysers. Knowledge of laboratory artefacts is crucial for the correct interpretation of results obtained using automated methods. SF pseudoeosinophilia has recently been described as a new artefact in patients with crystal-related arthropathies. We investigated whether pseudoeosinophilia of SF is restricted to crystal-related disorders, or if it may also occur in other arthropathies.

Methods: We compared the percentages of eosinophils in 120 crystal containing SF samples with 185 crystal-free specimens using the Wilcoxon test. Crystal positive samples, determined by polarised microscopy, contained at least two monosodium urate or calcium pyrophosphate crystals per 10 high power fields (630× magnification). True SF eosinophilia was ruled out by microscopic examination of stained slides.

Results: Crystal positive samples had significantly higher percentages of eosinophils than the controls (p<0.0001). No significant differences between the two crystal types were found (p=0.693). Thus, pseudoeosinophilia was significantly correlated with the presence of crystals, and none of the distinct crystal types was more likely to be associated with pseudoeosinophilia.

Conclusions: In this study, SF pseudoeosinophilia was confirmed as a crystal-related laboratory artefact which has to be considered in the interpretation of automated SF leukocyte differential counts.

Keywords: calcium pyrophosphate; eosinophilia; monosodium urate; pseudoeosinophilia; synovial fluid

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Christoph Robier, Franz Quehenberger, Manfred Neubauer, Mariana Stettin, and Franz Rainer
Clinical Chemistry and Laboratory Medicine (CCLM), 2012, Volume 50, Number 2

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