Joint Fluid Analysis Health Article

Microbiological analysis

All samples of synovial fluid should be cultured and Gram-stained. The Gram stain results can be definitive for septic arthritis if neutrophils and bacteria are found, but is not always positive. The fluid should be inoculated on blood agar plates; on chocolate (heated blood) agar plates for gonococcus and Haemophilus; and in broth such as thioglycolate for the isolation of anaerobic bacteria. N. gonorrhoeae is responsible for about 75% of septic arthritis in young and middle aged adults. Staphylococcus spp. account for about 75% of septic arthritis in the elderly. Staphylococcus, Streptococcus, and Haemophilus are the most common genera isolated from children.

Preparation

Prior to the procedure, any risks that are involved should be explained to the patient. The patient will be given a local anesthetic but no pain medications or sedatives are required. If the clinician requests a glucose test, the patient will be asked to fast for six to 12 hours before the procedure. If not, there is no special preparation required for a joint fluid analysis.

Aftercare

Some post-procedural pain may be experienced. For this reason, the patient should arrange to be driven home by someone else. Aftercare of the joints will depend on the results of the analysis.

KEY TERMS

Aspirate—The removal by suction of a fluid from a body cavity using a needle.

Bursae—A closed sac lined with a synovial membrane and filled with fluid, usually found in areas subject to friction, such as where a tendon passes over a bone.

Gout—A painful joint disease characterized by the deposition of uric acid crystals in the joint. These crystals cause swelling and redness.

Hematoma—A localized mass of blood that is confined within an organ or tissue.

Hyaluronic acid—A high molecular weight made of carbohydrate and glucuronic acid that is found in high concentrations in the synovial fluid. This provides thickness to the fluid so it can cushion the joint.

Joint—A moveable portion of bone found between two bones.

Lupus erythematosus—A multisystem disease with an autoimmune etiology. Lupus causes problems with the skin, kidneys, joints and the serosal membranes.

Rheumatiod arthritis—A chronic and progressive inflammation of the joints whose cause is unknown.

Synovial fluid—A transparent lubricating fluid secreted in a sac to protect an area where a tendon passes over a bone.

Complications

While joint fluid analysis is generally a safe procedure, especially when performed on a large, easily accessible joint, such as the knee, some risks are possible. Some of the complications to the procedure, although rare, include infection at the site of the needle stick, an accumulation of blood (hematoma) formation, local pain, injury to cartilage, tendon rupture, and nerve damage.

Results

Normal values typical for synovial fluid are shown below:

• Volume: 0.15-3.5 mL.
• Transparency: clear.
• Color: straw or pale yellow.
• Viscosity: 1.6 in (4 cm) thread or greater.
• Mucin clot: firm.
• Glucose: different from plasma by 10 mg/dL or less.
• Total protein: less than or equal to 2.0 g/dL.
• White blood cell count: less than 200 per microliter.
• Differential: less than 25% granulocytes.
• Crystals: negative.

Health care team roles

The removal of synovial fluid from a joint should be done by a physician. Laboratory tests are performed by clinical laboratory scientists/medical technologists. Physicians interpret the results of laboratory tests.

BOOKS

Burtis, Carl A. and Edward R. Ashwood. Tietz Textbook of Clinical Chemistry. Philadelphia: W.B. Saunders Company, 1999.

Kaplan, Lawrence A. and Amadeo J. Pesce. Clinical Chemistry, Theory, Analysis and Correlation. St. Louis: Mosby Publishers, 1996.

Stobo, John D., David B. Hellman, Paul W. Ladenson,, Brent G. Petty and Thomas A. Traill. Principles and Practice of Medicine, 23rd Edition. Stamford, CT: Appleton and Lange, 1996.

Jane E. Phillips, PhD