Finding the right tests…
Emergency services available 24 x 7
Emergency services available 24 x 7
Finding the right tests…
Haematology
Synovial fluid is the thick, lubricating fluid inside your joints, and this test examines a sample of it, usually drawn from a swollen or painful joint by a doctor using a needle, a procedure called arthrocentesis. The lab looks at the fluid's colour and clarity, counts and classifies the white cells in it, checks for crystals under a specialised microscope, and can culture it for bacteria. Together these findings help separate a few broad categories of joint problem from each other: mechanical wear and tear, crystal-related arthritis like gout, inflammatory arthritis, and joint infection. It's one of the more direct ways to investigate an unexplained joint effusion.
The report typically covers the fluid's appearance, a total white cell count with the percentage that are polymorphs, and whether crystals or organisms were seen. A relatively low white cell count with a clear, viscous appearance is more consistent with mechanical or degenerative joint problems, while a markedly high white cell count, especially one dominated by polymorphs, raises concern for infection. Crystal examination, done under polarised light, either confirms or rules out gout or pseudogout by identifying the specific crystal type. If infection is suspected, a Gram stain and culture are also run on the same sample.
When a joint becomes swollen or painful without an obvious cause, examining the fluid inside it is one of the most direct ways to find out why, because the fluid itself reflects what's happening in the joint space. A rheumatology reference used by clinicians divides results into broad categories based mainly on the white cell count and what's found on closer examination.
A noninflammatory pattern, generally under a couple thousand white cells per cubic millimetre, fits with osteoarthritis or mechanical joint problems. An inflammatory pattern, roughly two thousand to fifty thousand cells, points toward conditions like rheumatoid arthritis or gout. A count above fifty thousand, particularly with more than three-quarters of the cells being polymorphs, raises strong suspicion for septic arthritis, a bacterial joint infection that needs urgent treatment.
A cell count alone can suggest a category, but crystal examination under polarised light is what actually confirms gout or pseudogout by identifying monosodium urate or calcium pyrophosphate crystals. A Gram stain and culture are what confirm or rule out a bacterial infection, since even a very high cell count is a pattern rather than proof on its own. Because septic arthritis can damage a joint quickly if untreated, this combination of tests is often run urgently when infection is a real possibility.
A doctor draws it from the joint using a needle, in a procedure called arthrocentesis. It's usually done in a clinic setting with local anaesthetic to reduce discomfort.
It suggests inflammation. The higher the count, especially with a large share of polymorphs, the more concerning it is for a bacterial joint infection rather than a mechanical or mild inflammatory cause.
Yes. Examining the fluid under polarised light to identify monosodium urate crystals is considered the definitive way to confirm gout, rather than relying on symptoms alone.
If septic arthritis, a bacterial joint infection, is suspected, results guide treatment decisions quickly. An untreated joint infection can cause lasting joint damage.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Pseudogout is a crystal-related joint condition caused by calcium pyrophosphate crystals rather than the urate crystals seen in gout. The same polarised-light crystal examination used for gout can identify it.
Possibly. Synovial fluid examination is used for a range of joint problems beyond infection, including gout, pseudogout, and inflammatory arthritis, since the fluid pattern helps distinguish between them.