Joint Aspiration Laboratory Medicine

Updated: Nov 08, 2017
  • Author: Steven N Berney, MD; Chief Editor: Vinod K Panchbhavi, MD, FACS  more...
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Laboratory Medicine

Laboratory Medicine Summary

When aspirating a joint, make note of the appearance of the synovial fluid. Normal fluid is clear to light yellow and is viscous. Inflammatory fluid is darker yellow to cloudy 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 and covered with a cover slip then viewed immediately with a polarized light microscope.

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, use a sterile culture bottle. In particular cases it may be appropriate to order a mycobacterial culture or fungal culture.