Synovial fluid analysis

What it is

Synovial fluid falls into five categories on clinical and laboratory findings, using volume, clarity, color, viscosity, white blood cell count per mm3, polymorphonuclear leukocytes as a percent, and culture.

• Normal: volume under 3.5 mL at the knee, transparent, clear, high viscosity, white cells under 200, polymorphonuclear leukocytes under 25 percent, culture negative
• Noninflammatory: volume often over 3.5, transparent, yellow, high viscosity, white cells 0 to 2000, polymorphonuclear leukocytes under 25 percent, culture negative
• Inflammatory: often over 3.5, translucent-opaque, yellow, low viscosity, white cells over 2000 per mm3, polymorphonuclear leukocytes 50 percent or more, culture negative
• Septic: often over 3.5, opaque, yellow, variable viscosity, white cells over 20,000 per mm3, polymorphonuclear leukocytes 75 percent or more, culture often positive
• Hemorrhagic: usually over 3.5, bloody, red, variable viscosity, variable white cells, polymorphonuclear leukocytes 50 to 75 percent, culture negative

So viscosity is high in normal and noninflammatory fluid and low once it is inflammatory, clarity moves from transparent to translucent-opaque to opaque, and only the septic fluid gives a culture that is often positive. The two rows climb together: white cells under 200, then 0 to 2000, then over 2000, then over 20,000, with polymorphonuclear leukocytes under 25 percent, then under 25, then 50 or more, then 75 or more.