How is the synovial fluid analyzed following joint aspiration (arthrocentesis)?

Updated: Mar 23, 2020
  • Author: Steven N Berney, MD; Chief Editor: Vinod K Panchbhavi, MD, FACS  more...
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After aspiration of synovial fluid from a joint, it is important to make note of the appearance of the fluid. Normal fluid is clear to light yellow and is viscous. Inflammatory fluid is darker yellow to cloudy in appearance and loses its viscosity. Purulent fluid is coffee-colored to whitish and opaque.

A small amount of joint fluid can be placed on a microscope slide, covered with a cover slip, and then viewed immediately with a polarized light microscope.

The remaining synovial fluid can be sent to a laboratory for further analysis. Typical orders should include cell count, Gram stain, culture, and crystal analysis. Most commercial laboratories perform these tests on a green top (heparinized) tube. If more fluid is present or if septic arthritis is the leading differential, a sterile culture bottle should be used. In particular cases it may be appropriate to order a mycobacterial culture or a fungal culture.

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