title: A 3-day delay in synovial fluid crystal identification did not hinder the reliable detection of monosodium urate and calcium pyrophosphate crystals.
abstract: BACKGROUND
  Arthrocentesis is an essential emergency step in managing patients with acute arthritis. To identify a bacterial infection, Gram staining is performed promptly. However, crystal analysis may not be immediately performed in many facilities. Being considered not to be stable over time, synovial fluid (SF) is sometimes discarded instead of being stored for crystal identification.
  
  
  OBJECTIVE
  The aim of this study was to assess the detectability of monosodium urate (MSU) and calcium pyrophosphate (CPP) crystals in SF over a period of 3 days.
  
  
  METHODS
  Consecutive SF samples from 75 joints were analyzed for MSU, CPP crystals, and pH. Two independent observers evaluated the samples by regular light and polarization microscopy immediately after arthrocentesis and after 1, 2, and 3 days at room temperature or at 4°C.
  
  
  RESULTS
  Of 75 samples, 27 contained crystals (16 MSU, 6 CPP, 5 both); semiquantitative counts of both MSU and CPP crystals did not change significantly after 3 days. There was no new formation of crystals in any of the crystal-negative samples, which was independent of the storage temperature. Synovial fluid pH was not predictive of crystals and did not change over time.
  
  
  CONCLUSIONS
  Although immediate workup for microbiology, including Gram stain and culture, is indispensable and well established, crystal analysis may at times not be immediately performed. Our study suggests that when crystal identification cannot be done immediately, it can be safely performed up to 3 days after arthrocentesis when SF is stored at 4°C or even at stable room temperature (20°C).
authors.affiliation: Department of Rheumatology, University Clinic Carl Gustav Carus, Technical University of Dresden, Dresden, Germany. anne-kathrin.tausche@uniklinikum-dresden.de
authors.forename: Anne-Kathrin
authors.initials: AK
authors.lastname: Tausche
authors.forename: Siegmund
authors.initials: S
authors.lastname: Gehrisch
authors.forename: Ines
authors.initials: I
authors.lastname: Panzner
authors.forename: Maria
authors.initials: M
authors.lastname: Winzer
authors.forename: Ursula
authors.initials: U
authors.lastname: Range
authors.forename: Stefan R
authors.initials: SR
authors.lastname: Bornstein
authors.forename: Gabriele
authors.initials: G
authors.lastname: Siegert
authors.forename: Carsten
authors.initials: C
authors.lastname: Wunderlich
authors.forename: Martin
authors.initials: M
authors.lastname: Aringer
mesh_terms: D001170:Arthritis, Infectious / Q000175:diagnosis*; D002131:Calcium Pyrophosphate / Q000032:analysis*; D016009:Chi-Square Distribution; D003460:Crystallization; D006801:Humans; D006863:Hydrogen-Ion Concentration; D019152:Paracentesis / Q000379:methods*; D011446:Prospective Studies; D018709:Statistics, Nonparametric; D013582:Synovial Fluid / Q000737:chemistry*; D014527:Uric Acid / Q000032:analysis*
chemical_list: D014527:Uric Acid; D002131:Calcium Pyrophosphate