title: Calcium pyrophosphate and monosodium urate crystals in synovial fluid as a cause of pseudoeosinophilia.
abstract: 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.
authors.affiliation: Department of Internal Medicine, Hospital Barmherzige Brueder Graz-Eggenberg, Graz, Austria.
authors.forename: Christoph
authors.initials: C
authors.lastname: Robier
authors.affiliation: Department of Internal Medicine, Hospital Barmherzige Brueder Graz-Eggenberg, Graz, Austria.
authors.forename: Manfred
authors.initials: M
authors.lastname: Neubauer
authors.affiliation: Institute of Medical Informatics, Statistics and Documentation, Medical University of Graz, Austria.
authors.forename: Franz
authors.initials: F
authors.lastname: Quehenberger
authors.affiliation: Department of Internal Medicine, Hospital Barmherzige Brueder Graz-Eggenberg, Graz, Austria.
authors.forename: Mariana
authors.initials: M
authors.lastname: Stettin
authors.affiliation: Department of Internal Medicine, Hospital Barmherzige Brueder Graz-Eggenberg, Graz, Austria.
authors.forename: Franz
authors.initials: F
authors.lastname: Rainer
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002131:Calcium Pyrophosphate / Q000737:chemistry*; D003460:Crystallization; D003951:Diagnostic Errors; D004802:Eosinophilia / Q000175:diagnosis*; D005260:Female; D006801:Humans; D007958:Leukocyte Count; D008297:Male; D008859:Microscopy, Polarization; D008875:Middle Aged; D013582:Synovial Fluid / Q000737:chemistry / Q000166:cytology*; D014527:Uric Acid / Q000737:chemistry*
chemical_list: D014527:Uric Acid; D002131:Calcium Pyrophosphate