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Tests and diagnosis
By Mayo Clinic staffYour doctor will examine your knee thoroughly and may recommend diagnostic tests. If the underlying cause of water on the knee is unknown, he or she will want to know why you've developed this condition.
Diagnostic tests include:
- X-ray. Your doctor will request an X-ray to make sure you haven't broken or dislocated any bones or to determine if you have arthritis.
- MRI. This test detects abnormalities of the bone or knee joint, such as a tear in your ligaments, tendons or cartilage.
- Joint aspiration (arthrocentesis). During this procedure your doctor withdraws fluid from inside your knee for analysis such as cell count, culture for bacteria, and examination for crystals, such as uric acid or calcium pyrophosphate dihydrate (CPPD) crystals found in gout or pseudogout.
- Blood tests. If your knee is swollen, red and warm to the touch when compared to your other knee, your doctor may be concerned about inflammation due to rheumatoid arthritis or a crystalline arthritis, such as gout or pseudogout, or joint infection. Besides sending the joint fluid to the lab for analysis, he or she may request blood tests to determine your white blood cell count, erythrocyte sedimentation rate, and perhaps the level of C-reactive protein or uric acid.
