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Synovial Fluid: Total Leukocyte Count

- Discussion:
    - 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.
    - Disease         
            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.
    - Disease                         
            - JRA 15,000- 80,000 and 75% polymorphs
            - Septic Arthritis 80,000-200,000 and > 75% polymorphs
            - Pseudogout
- 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.

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