title: Pseudoeosinophilia of synovial fluid is caused by crystals mimicking the distinct light scattering fractions of eosinophilic granules.
abstract: BACKGROUND
  Automated leukocyte differential counts of synovial fluid (SF) can be influenced by laboratory artefacts. Pseudoeosinophilia of SF has recently been first described in association with monosodium urate and calcium pyrophosphate crystals. This study compared automated measurements of the percentages of SF leukocyte fractions by two haematology analysers in order to elucidate the underlying mechanism of pseudoeosinophilia.
  
  
  METHODS
  The percentages of the leukocyte fractions of 17 crystal-containing and 28 crystal-free specimens were compared using the Wilcoxon test. Measurements were performed using the Cell-Dyn 3200 and the ADVIA 2120i, which are based on different techniques.
  
  
  RESULTS
  The percentages of eosinophils of the crystal-positive samples determined by the Cell-Dyn 3200 were significantly higher than those assessed by the ADVIA (p<0.0001), whereas the percentages of eosinophils of the controls did not differ significantly between the two devices (p=0.95). The Cell-Dyn 3200 clearly showed the phenomenon of crystal-associated pseudoeosinophilia (p<0.0001), which did not occur in the ADVIA measurements (p=0.28). The percentage of neutrophils was to a lower degree elevated in the crystal group (p=0.015).
  
  
  CONCLUSIONS
  It was confirmed that SF crystals interfere with the typical light scattering fractions of leukocyte granules and may thus lead to spuriously elevated percentages of eosinophils and neutrophils in SF specimens.
authors: Central Laboratory, Department of Internal Medicine, Hospital Barmherzige Brueder Graz-Eggenberg, Graz, Austria. christoph.robier@bbegg.at
authors: Christoph
authors: C
authors: Robier
authors: Franz
authors: F
authors: Quehenberger
authors: Manfred
authors: M
authors: Neubauer
authors: Mariana
authors: M
authors: Stettin
authors: Franz
authors: F
authors: Rainer
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002131:Calcium Pyrophosphate / Q000737:chemistry; D004802:Eosinophilia / Q000175:diagnosis* / Q000473:pathology; D004804:Eosinophils / Q000737:chemistry*; D005260:Female; D006801:Humans; D008297:Male; D008853:Microscopy; D008875:Middle Aged; D012015:Reference Standards; D015203:Reproducibility of Results; D013582:Synovial Fluid / Q000737:chemistry*; D014527:Uric Acid / Q000737:chemistry
chemical_list: D014527:Uric Acid; D002131:Calcium Pyrophosphate