To determine whether a horse's joint is infected—which can be a serious side effect of joint injections or lower limb wounds—veterinarians analyze synovial (joint) fluid samples for signs of trouble. Collecting synovial fluid can be a tricky procedure, however, and can result in a blood-contaminated sample. While veterinarians have historically tossed such samples and started over—at the expense of the horse's welfare as well as the owner's wallet—researchers now believe useful information can still be garnered.

James Carmalt, MA, VetMB, MVetSc, FRCVS, Dipl. ABVP, ACVS, professor of equine surgery at the University of Saskatchewan's Western College of Veterinary Medicine, in Saskatoon, described how veterinarians can effectively use and interpret blood-contaminated synovial fluid samples at the 2013 American Association of Equine Practitioners convention, held Dec. 7-11 in Nashville, Tenn.

Normal synovial fluid is straw-colored, transparent, and highly viscous, Carmalt said. When veterinarians assess this fluid for signs of infection, they are looking for elevated total protein (TP) concentrations and white blood cell (WBC) counts.

"Unfortunately, it is not uncommon for an equine practitioner to be unable to provide a definitive diagnosis of septic arthritis for multiple reasons, including a blood-contaminated sample," Carmalt said