- 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.
Synovial leukocytosis in infectious arthritis.
How sensitive is the synovial fluid white blood cell count in diagnosing septic arthritis?
Does this adult patient have septic arthritis?
Diagnostic utility of laboratory tests in septic arthritis.
Laboratory tests in adults with monoarticular arthritis: can they rule out a septic joint?
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?