A joint fluid culture is a laboratory test that uses your joint fluid to identify organisms that can cause infection. The actual culture test takes place in a laboratory and does not involve the patient. The joint fluid is also used to test for the presence of protein, glucose, or crystals (such as monosodium urate monohydrate or calcium pyrophosphate dihydrate that can cause gout and pseudogout respectively). The number of white and red blood cells in the fluid can be also be determined.
You may experience pain and discomfort in your joints due to a sprain, sports injury, misuse as a result of repetitive movements or an inflammatory arthritis caused by an immune condition. If you have chronic pain or inflammation in the joints without an apparent cause, your doctor may order a joint fluid culture to help diagnose a variety of conditions, including several forms of arthritis, gout, and joint infections.
How Is the Joint Fluid Obtained?
A joint aspiration procedure can be performed as part of a hospital stay, on an outpatient basis in a hospital, or at the doctor’s office.
As preparation for removal of joint fluid, you may be asked to remove your clothing and put on a hospital gown. An antiseptic will be used to clean the site where the sample is to be obtained from and the entire procedure is done under sterile conditions Joint aspiration is usually performed using a local anesthetic near the site where the needle will be inserted to remove the joint fluid. Most often done on the knee, joint aspiration can also be done on hips, ankles, shoulders, elbows, and wrists.
Your doctor will remove fluid from your joint using a needle and syringe in a procedure called a joint aspiration. You will feel a needle stick and possibly a slight stinging sensation. The doctor will draw a small sample of fluid into the syringe. Then, the needle will be removed and a dressing applied over the injection site.
In addition to obtaining fluid for a joint fluid culture, joint aspiration may also be used to relieve pressure due to fluid that is collecting around the joint. Conditions like bursitis can cause liquid to collect around a joint. In some cases, medication is injected into the joint after the fluid is removed. This is effective in treating bursitis and tendonitis.
After the sample is collected, it is sent to a laboratory where it can be tested for cells, glucose, protein, crystals, and organisms such as bacteria, fungi, and viruses.
Preparing for Joint Aspiration
Tell your doctor if you are taking any prescription drugs, over-the-counter medications or supplements, are pregnant, or have a history of bleeding disorders. In some cases, you may be instructed to fast before the procedure, but there is no other preparation required. Ask your doctor for specific instructions based on your medical condition.
After the Joint Aspiration
You will be able to go home shortly after the procedure. Keep the aspiration site clean and dry, removing the dressing as advised by your doctor. Aspirin may cause bleeding after the procedure, so ask your doctor which pain relievers you should take.
Risks of Joint Aspiration
Joint aspiration is considered a safe procedure. It is normal for your joint to feel sore, uncomfortable, or appear bruised for a few days. However, if you experience any of the following symptoms, contact your doctor immediately:
- redness or swelling
- bleeding or other discharge from the aspiration site
- increasing pain at the site
- restricted range of motion of the joint
These symptoms could be signs of infection and should be treated as quickly as possible.
Interpreting the Results
The laboratory will send a report to your doctor, who will then review it with you. If abnormalities are discovered, additional tests may be necessary to narrow down the cause and assess treatment options. Pain and swelling of your joint may be due to a variety of conditions other than injury, gout or inflammatory arthritis, including bacterial arthritis, fungal arthritis, gonococcal arthritis, or tuberculosis arthritis.
Your doctor will recommend treatments based on the specific results.