What Is a Joint Fluid Culture?

A culture of your joint fluid is a laboratory test. It identifies organisms that can cause infection in your joint fluid. The actual culture test takes place in a laboratory. The joint fluid is also used to test for the presence of protein, glucose, or crystals. For example, the presence of monosodium urate monohydrate crystals indicates you may have gout. The culture can also determine the number of white and red blood cells in the fluid.

You may experience pain and discomfort in your joints due to:

  • a sprain
  • a sports injury
  • repetitive movements
  • 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.

Before you have a joint fluid culture, tell your doctor if you’re taking any prescription drugs or over-the-counter medications or supplements. Also, tell your doctor if you’re pregnant or have a history of bleeding disorders. You may need to fast before the procedure, but there’s no other preparation required. Ask your doctor for specific instructions based on your medical condition.

Your doctor will get a sample of your joint fluid by performing a joint aspiration. A joint aspiration procedure can occur:

  • during a hospital stay
  • on an outpatient basis in a hospital
  • at the doctor’s office

As preparation for the removal of joint fluid, you’ll remove your clothing and put on a hospital gown. Your doctor will clean the site of the aspiration. The entire procedure occurs under sterile conditions. The doctor may do a joint aspiration using a local anesthetic near the site of the needle insertion. Joint aspiration is usually performed on the knee, but it may also be performed on your:

  • hips
  • ankles
  • shoulders
  • elbows
  • wrists

Your doctor will remove fluid from your joint using a needle and syringe in a procedure called a joint aspiration. You’ll feel a needlestick and possibly a slight stinging sensation. The doctor will draw a small sample of fluid into the syringe. Then, they’ll remove the needle and apply a bandage over the injection site.

Joint aspiration can also relieve pressure due to fluid collecting around the joint. Conditions like bursitis can cause liquid to collect around a joint. In some cases, a doctor will inject medication into the joint after removing the fluid if they’re certain that an infection doesn’t exist. Usually, this medication will be a corticosteroid, which is a medication that reduces inflammation. This is effective in treating bursitis and tendonitis. However, the relief is often temporary. The Cleveland Clinic notes that it’s common for fluid to collect around the joint again.

After collecting the sample, your doctor will send it to a laboratory for testing. The lab will test the fluid sample for:

  • blood cells
  • glucose
  • protein
  • crystals
  • organisms, such as bacteria, fungi, and viruses

You’ll be able to go home shortly after the procedure. Keep the aspiration site clean and dry. Remove the bandage as advised by your doctor. Aspirin may cause bleeding after the procedure. You should ask your doctor which pain relievers you should take. Because your joint may swell again, your doctor may recommend that you elevate the extremity and apply an ice bag to your joint.

Doctors consider joint aspiration to be a safe procedure. It’s normal for your joint to feel sore, uncomfortable, or appear bruised for a few days. However, contact your doctor immediately if you experience:

  • a fever
  • redness
  • swelling
  • bleeding
  • discharge from the aspiration site
  • an increasing amount of pain at the aspiration site
  • a restricted range of motion in the joint

These symptoms could be signs of infection and need quick treatment.

The laboratory will send a report to your doctor. Your doctor will then review it with you. If the lab found abnormalities, you may need other tests 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. Some of the other possible causes include:

  • bacterial arthritis
  • fungal arthritis
  • gonococcal arthritis
  • tuberculosis arthritis

Your doctor will recommend treatments based on the specific results of your test.