- synovial fluid should be cultured if there is any suggestion of infection.
- normal synovial fluid:
- contains < 60 to 180 cells per ml, most of which should be mononuclear;
- fluid is considered to be "noninflammatory" if it contains < 2000 cells / ml, but most samples of synovial fluids from pts w/ DJD contain < 500 cells per ml;
- diff dx:
- bacterial arthritis:
- usually causes most intense synovial fluid leukocytosis, w/ 50,000 to 200,000 cells / ml and usually over 90% PMNs;
- synovial-fluid leukocyte count is rarely < 20,000 cells per ml;
- lower leukocyte counts are more common early in course of bacterial arthritis and in pts w/ disseminated GC infection;
- gout, pseudogout, acute rheumatic fever, Reiter's disease, and RA can cause a markedly inflammatory synovial effusion;
- finding of > 90% PMNs despite relatively low total leukocyte count should prompt concern about infection or crystal-induced disease;
- Greater > 2000 leukocytes/ml;
- considered to be affected by an inflammatory process.
- as the leukocyte count increases, so does suspicion of infection.
Traumatic < 5,000 (w/ RBCs)
Toxic Synovitis 5,000- 15,000 and less than < 25 % polymorphs
Acute Rheumatic F. 10,000- 15,000 and 50 % polymorphs
JRA 15,000- 80,000 and 75 % polymorphs
- Greater > 50,000 leukocytes/ml;
- although other dzs, including trauma, may produce WBC cells in joint fluid, levels > 50,000/mm3 are usually due to infectious arthritis.
- JRA 15,000- 80,000 and 75% polymorphs
- Septic Arthritis 80,000-200,000 and > 75% polymorphs
- Greater > 100,000 leukocytes/ml;
- conventional wisdom is that effusions containing > 100,000 leukocytes per cubic ml are septic, but this is more a guideline than a rule.
Towards evidence based emergency medicine: Best BETs from the Manchester Royal Infirmary. BET 3: Is the white cell count of the joint aspirate sufficiently sensitive/specific to rule in/out septic arthritis?