Feasibility of a tetracycline-binding method for detecting synovial fluid basic calcium phosphate crystals.
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.
Rosenthal
Ann K
AK
Medical College of Wisconsin and the Zablocki VA Medical Center, Milwaukee, Wisconsin 53295-1000, USA. ann.rosenthal@med.va.gov
Fahey
Mark
M
Gohr
Claudia
C
Burner
Todd
T
Konon
Irina
I
Daft
Laureen
L
Mattson
Eric
E
Hirschmugl
Carol
C
Ryan
Lawrence M
LM
Simkin
Peter
P
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*
D010118:Oxytetracycline; D002131:Calcium Pyrophosphate