title: Feasibility of a tetracycline-binding method for detecting synovial fluid basic calcium phosphate crystals.
abstract: OBJECTIVE
  Basic calcium phosphate (BCP) crystals are common components of osteoarthritis (OA) synovial fluid. Progress in understanding the role of these bioactive particles in clinical OA has been hampered by difficulties in their identification. Tetracyclines stain calcium phosphate mineral in bone. The aim of this study was to investigate whether tetracycline staining might be an additional or alternative method for identifying BCP crystals in synovial fluid.
  
  
  METHODS
  A drop of oxytetracycline was mixed with a drop of fluid containing synthetic or native BCP, calcium pyrophosphate dihydrate (CPPD), or monosodium urate (MSU) crystals and placed on a microscope slide. Stained and unstained crystals were examined by light microscopy, with and without a portable broad-spectrum ultraviolet (UV) pen light. A small set of characterized synovial fluid samples were compared by staining with alizarin red S and oxytetracycline. Synthetic BCP crystals in synovial fluid were quantified fluorimetrically using oxytetracycline.
  
  
  RESULTS
  After oxytetracycline staining, synthetic and native BCP crystals appeared as fluorescent amorphous aggregates under UV light. Oxytetracycline did not stain CPPD or MSU crystals or other particulates. Oxytetracycline staining had fewer false-positive test results than did alizarin red S staining and could provide estimates of the quantities of synthetic BCP crystals in synovial fluid.
  
  
  CONCLUSIONS
  With further validation, oxytetracycline staining may prove to be a useful adjunct or alternative to currently available methods for identifying BCP crystals in synovial fluid.
authors.affiliation: Medical College of Wisconsin and the Zablocki VA Medical Center, Milwaukee, Wisconsin 53295-1000, USA. ann.rosenthal@med.va.gov
authors.forename: Ann K
authors.initials: AK
authors.lastname: Rosenthal
authors.forename: Mark
authors.initials: M
authors.lastname: Fahey
authors.forename: Claudia
authors.initials: C
authors.lastname: Gohr
authors.forename: Todd
authors.initials: T
authors.lastname: Burner
authors.forename: Irina
authors.initials: I
authors.lastname: Konon
authors.forename: Laureen
authors.initials: L
authors.lastname: Daft
authors.forename: Eric
authors.initials: E
authors.lastname: Mattson
authors.forename: Carol
authors.initials: C
authors.lastname: Hirschmugl
authors.forename: Lawrence M
authors.initials: LM
authors.lastname: Ryan
authors.forename: Peter
authors.initials: P
authors.lastname: Simkin
mesh_terms: D000818:Animals; D002131:Calcium Pyrophosphate / Q000032:analysis*; D005240:Feasibility Studies; D006651:Histocytochemistry / Q000379:methods; D006801:Humans; D008860:Microscopy, Ultraviolet / Q000295:instrumentation; D010118:Oxytetracycline; D034421:Sus scrofa; D013582:Synovial Fluid / Q000737:chemistry*
chemical_list: D010118:Oxytetracycline; D002131:Calcium Pyrophosphate