Joint Fluid Analysis

Arthrocentesis, Synovial Fluid Analysis

Results

Joint 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

	Normal	Abnormal
Color and clarity	Clear to light yellow	Red (bloody) or milky white (cloudy)
Blood cell count	No large numbers of red or white blood cells	Large numbers of red or white blood cells
Crystals (seen under a special microscope with polarized light)	Not present	Present
Gram stain and culture	No bacteria are seen and no organisms grow in the culture.	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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Author:	Shannon Erstad, MBA/MPH	Last Updated: June 12, 2008
Medical Review:	Kathleen Romito, MD - Family Medicine Stanford M. Shoor, MD - Rheumatology
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