Lab Tests

What do the results of a synovial fluid analysis mean?

A Answers (1)

  • AHealthwise answered

    A synovial fluid analysis is a test to look at joint fluid under a microscope for problems such as infection, gout, pseudogout, inflammation, or bleeding. The test can help find the cause of joint pain or swelling.

    The results of a joint fluid analysis are usually available the same day. The results from a culture are usually available in a few days.

    Joint fluid analysis

    Color and Clarity

    • Normal: Clear to light yellow
    • Abnormal:  Red (bloody) or milky white (cloudy)
    Blood cell count
    • Normal: No large numbers of red or white blood cells 
    • Abnormal: Large numbers of red or white blood cells
    Crystals (seen under a special microscope with polarized light)
    • Normal: Not present 
    • Abnormal: Present
    Gram stain and culture
    • Normal: No bacteria are seen and no organisms grow in the culture. 
    • Abnormal: Bacteria are seen or organisms grow in the culture.
      Abnormal values
      • Color and clarity. Slightly cloudy fluid may be caused by inflammation, gout or pseudogout. A deep, dark red color may be caused by bleeding in the joint. Milky white may be caused by infection or inflammation.
      • Blood cell count. Large numbers of red blood cells may be caused by bleeding in the joint from injury, inflammation or abnormal clotting of the blood. Large numbers of white blood cells may be caused by gout, pseudogout, other types of arthritis (such as rheumatoid arthritis), psoriatic arthritis, injury or infection.
      • Presence of crystals. Uric acid crystals in the joint mean you have gout. Calcium pyrophosphate crystals mean you have pseudogout.
      • Gram stain and culture. Bacteria seen under a microscope on the Gram stain (a special dye) of the joint fluid may be caused by an infection. Bacteria that grows out of a culture plate in 1 to 2 days confirms the presence of an infection.

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