Synovial Fluid: Total Leukocyte Count : Wheeless' Textbook of Orthopaedics

- 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.