What to know about synovial (joint) fluid analysis
Many joints contain small amounts of synovial fluid, which helps keep the joint lubricated and able to move smoothly. Most joints, including the knees and hips, are synovial joints.
When a person has painful or swollen joints, a doctor can extract and analyze a sample of their synovial fluid to help determine the cause of these symptoms.
Synovial joint analysis can help a doctor diagnose and monitor the following:
- inflammatory conditions, such as gout or RA
- degenerative conditions, including osteoarthritis
- bleeding conditions
In this article, we look at the procedure of synovial fluid analysis, including the results and risks.
Synovial fluid analysis procedure
A doctor can perform a synovial fluid analysis to help diagnose joint conditions.
During a synovial fluid analysis, a doctor will extract and analyze a sample of synovial fluid from the joint. Doctors may refer to the collection of synovial fluid as arthrocentesis.
During the procedure, a healthcare professional will typically follow these steps:
- numb the area around the affected joint using a local anesthetic injection or a numbing spray
- insert a needle and syringe into the joint between the two bones
- draw out a small sample of synovial fluid through the syringe and deposit it into a container
- send the sample to a laboratory for analysis
The procedure is quick and relatively painless.
What do the results mean?
Synovial fluid analysis assesses a person's synovial fluid for signs of inflammation, swelling, bleeding, and other joint abnormalities.
Doctors may look for several different types of change, including the following:
Abnormal appearance of synovial fluid
If a doctor finds a greater quantity of fluid than usual or it has a reduced thickness, this can indicate inflammation. Synovial fluid should be viscous, meaning that it is thick and sticky.
Synovial fluid that is an abnormal color can indicate inflammation. Synovial fluid is usually clear and colorless, but abnormal fluid can appear cloudy and colored. This suggests that microscopic or chemical changes have occurred. In this case, a doctor may recommend additional analysis.
The presence of microscopic organisms can indicate an infection.
A technician will analyze the fluid sample for microscopic properties that could indicate a health condition. These may include:
- an abnormally high white blood cell count, which could indicate gout, RA, or septic arthritis
- an abnormally high red blood cell count, which could indicate a bleeding disorder
- the presence of crystals, which can signify gout or pseudogout
- the presence of microorganisms, such as bacteria or fungi, which could be due to an infection
Other tests, such as gram stain or culture tests, can also detect the presence of microorganisms.
Doctors cannot diagnose a condition based on the results of a synovial fluid analysis alone, but this test can help them make an accurate diagnosis. For a complete diagnosis, a doctor will also need to consider a person's medical history, conduct imaging tests, and carry out a physical examination.
A doctor may also order other blood or urine tests alongside the synovial fluid analysis to help them make a diagnosis. For example, they can rule out infection using a blood culture test, which tells them whether or not a person has an infection elsewhere in the body.
Risks of a synovial fluid analysis
Synovial fluid analysis is a very safe procedure when a doctor performs it in sterile conditions.
People may experience some bleeding or soreness around the site of injection after the procedure, but this should not last long.
If the needle were not sterile, this could cause an infection. However, this scenario is unlikely to occur.
Synovial fluid analysis is a procedure that doctors use to help them diagnose several joint-related conditions, including RA, osteoarthritis, and gout. It also allows them to rule out infection as the cause of symptoms.
Signs of a medical condition may include the abnormal appearance of synovial fluid, changes in its chemical makeup, or the presence of crystals.
A doctor will use synovial fluid analysis alongside other diagnostic tests to determine the cause of a person's joint pain and inflammation.