Absolute and relative cell counts for synovial fluid from clinically normal shoulder and stifle joints in cats.

Objective: To determine absolute and relative cell counts for synovial fluid from grossly, radiographically, and histologically normal shoulder and stifle joints in healthy cats.

Design: Clinical study.

Animals: 52 cats scheduled to be euthanatized for unrelated reasons.

Procedure: Arthrocentesis of the shoulder and stifle joints was performed bilaterally, and synovial fluid was analyzed for absolute WBC count, WBC morphology, and percentages of neutrophils and mononuclear cells. Joints were examined grossly and radiographically, and synovial membrane specimens were submitted for histologic examination. Synovial fluid samples that were contaminated with blood and samples from joints with any gross, radiographic, or histologic abnormalities were excluded.

Results: 82 of the 208 synovial fluid samples were excluded because abnormalities were identified during physical examination; the volume of fluid obtained was insufficient for analysis; there was evidence of blood contamination; or the joint had gross, radiographic, or histologic abnormalities. Median WBC count for the remaining 126 synovial fluid samples was 91 cells/microL (96.4% mononuclear cells and 3.6% neutrophils); WBC count was not significantly different between left and right joint samples or between shoulder and stifle joint samples. Body weight was associated with synovial fluid WBC count, with WBC count increasing as body weight increased. Sixteen of the 52 (30%) cats had radiographic evidence of osteoarthritis involving at least 1 joint.

Conclusions And Clinical Relevance: Results suggest that synovial fluid can be obtained reliably from shoulder and stifle joints in cats.