Classification of Synovial Effusions
Examination | Normal | Hemorrhagic | Infectious | Inflammatory | Noninflammatory |
|---|---|---|---|---|---|
Gross examination | |||||
Appearance | Clear | Bloody | Turbid or purulent | Yellow, cloudy | Straw-colored, clear |
Routine laboratory examination | |||||
Culture | Negative | Negative | Often positive | Negative | Negative |
Polymorphonuclear leukocyte %* | < 25 | — | Usually >85 | > 50 | < 25 |
White blood cell count* | <200/mcL | Affected by amount of blood | 5,000–>100,000/mcL | 1,000–50,000/mcL | 200–1000/mcL |
* White blood cell (WBC) count and polymorphonuclear leukocyte % in infectious arthritis are lower if the organism is less virulent (eg, in gonococcal, Lyme, tuberculous, or fungal arthritis) or partially treated. Some effusions in systemic lupus erythematosus and other systemic rheumatic diseases are only equivocally inflammatory, with a WBC count of 500–2000/mcL. Noninfectious effusions rarely have up to 100,000 WBC/mcL. | |||||