A synovial fluid test is the most definitive way of determining a diagnosis of gout.

What is gout?  With this test, doctors can tell whether your pain results from uric acid crystals — meaning you do have gout — or from a different cause.

What Is Synovial Fluid?

The fluid inside joints is called synovial fluid. It lubricates joints to keep them moving smoothly.

  • Synovial fluid is similar to the oil in your car in that it prevents hard surfaces from grinding against one another.
  • During a gout attack, this fluid fills up with uric acid crystals. The crystals become lodged inside the joint when uric acid changes from a liquid state in the bloodstream to a solid, crystallized state inside the joint.
  • Having uric acid crystals in a joint’s synovial fluid is like getting sand in your car’s oil.

How Is the Test Done?

No special preparation is needed in advance of a synovial fluid test.

The doctor inserts a needle into the inflamed joint to extract a small amount of synovial fluid. This procedure, called arthrocentesis or joint aspiration, can be done in a doctor’s office, an outpatient clinic, or an emergency department.

The entire procedure takes about a half hour, but the actual aspiration only takes a couple of minutes.


Synovial Fluid Analysis

The collected sample of synovial fluid will be sent to a laboratory, where a technician will:

  • Assess the color and clarity, which indicates whether inflammation is present.
  • Look for uric acid crystals or other types of crystals like those found with pseudogout.
  • Look for bacteria, which could point to an infection.

Test Results

The synovial fluid test determines whether you have gout, pseudogout, rheumatoid arthritis, septic arthritis, or some other condition.

  • Gout — the test will show crystals made of uric acid.
  • Pseudogout — the test will show crystals made of calcium pyrophosphate (CPP), not uric acid.
  • Septic arthritis — the test will show a bacterial infection.
  • Rheumatoid arthritis — the test will show no crystals or bacteria, but a lot of inflammation.

  Bottom Line:  A synovial fluid test is the only way to determine conclusively whether you have gout, pseudogout, septic arthritis, or some other condition. Having this test will provide direction for overcoming your pain as quickly as possible.

(click here to learn more about home testing meters for blood uric acid)