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Joint Fluid Analysis

Test Overview

Joint fluid analysis is a test to look at joint fluid under a microscope for problems such as infection, gout, pseudogout, inflammation, or bleeding. The test can help find the cause of joint pain or swelling.

Normally, only a small amount of joint fluid is found in a joint. Joint fluid acts as a lubricant for the joint and cushions joint structures. If you have a joint problem, you may have more fluid in your joint and your joint may become swollen, stiff, and painful.

A sample of joint fluid can be taken from any joint in your body. The joint fluid is then analyzed in a lab to look for inflammation, infection, gout, pseudogout, or bleeding.

Why It Is Done

Joint fluid analysis is done to find inflammation, infection, gout, or pseudogout. Removing some of the joint fluid may also relieve pain caused by the buildup of fluid in your joint.

How To Prepare

Tell your doctor if you:

  • Have had bleeding problems, take aspirin or some other blood thinner, or take over-the-counter medicines, such as ibuprofen (Advil, Motrin) or naproxen (Aleve). Your doctor will tell you when you should stop taking these medicines several days before your procedure. Make sure that you understand exactly what he or she wants you to do.
  • Are allergic to any medicines, including anesthetics.
  • Are or might be pregnant.

Talk to your doctor about any concerns you have about the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form .

How It Is Done

Joint fluid analysis takes about 20 minutes and can be done in your doctor's office, clinic, operating room, or emergency room. Depending on which joint will be examined, you may be asked to undress and put on a hospital gown. You will sit or lie down on an examining table.

Your doctor will examine the joint to determine where the needle should be inserted. The skin over the joint area will be cleaned with antiseptic solution. A local anesthetic is often injected into the skin over the joint. For young children, a sedative may also be given.

A long, thin needle is slowly inserted in the joint area. A syringe attached to the needle is used to remove a sample of joint fluid. Samples of the fluid may be put in special tubes or containers and sent to the lab. A cortisone shot may be given into the joint before the needle is removed, to help keep fluid from building up again.

A tight (pressure) bandage will be placed over the site to reduce swelling and bruising. An elastic bandage may also be wrapped around your joint, such as your knee, to reduce swelling.

How It Feels

You will feel a prick or sting when the anesthetic is given. You may feel tingling, pressure, pain, or fullness in your joint as the fluid is removed.


There is very little chance of having a problem after a joint fluid analysis. Infection, bleeding, or damage to the tendon, nerve, or joint is rare.

Sometimes your doctor may not be able to draw any fluid out. The joint space may be too small, you may have scar tissue in the joint space, or there may not be any fluid in the joint.

The joint may be sore for 1 to 2 days after the procedure. If you have a cortisone shot, you may have some soreness or irritation at the site of the shot for 1 to 2 days. Avoid strenuous use of the joint for 2 to 3 days.


Joint fluid analysis is a test to look at joint fluid under a microscope for problems such as infection, gout, pseudogout, inflammation, or bleeding. The test can help find the cause of joint pain or swelling.

The results of a joint fluid analysis are usually available the same day. The results from a culture are usually available in a few days.

Joint fluid analysis



Colour and clarity

Clear to light yellow

Red (bloody) or milky white (cloudy)

Blood cell count

No large numbers of red or white blood cells

Large numbers of red or white blood cells

Crystals (seen under a special microscope with polarized light)

Not present


Gram stain and culture

No bacteria are seen and no organisms grow in the culture.

Bacteria are seen or organisms grow in the culture.

Abnormal values

  • Colour and clarity. Slightly cloudy fluid may be caused by inflammation, gout, or pseudogout. A deep, dark red colour may be caused by bleeding in the joint. Milky white may be caused by infection or inflammation.
  • Blood cell count. Large numbers of red blood cells may be caused by bleeding in the joint from injury, inflammation, or abnormal clotting of the blood. Large numbers of white blood cells may be caused by gout, pseudogout, other types of arthritis (such as rheumatoid arthritis), psoriatic arthritis, injury, or infection.
  • Presence of crystals. Uric acid crystals in the joint mean you have gout. Calcium pyrophosphate crystals mean you have pseudogout.
  • Gram stain and culture. Bacteria in the joint fluid that are causing an infection may be seen under a microscope after being coloured with a Gram stain (a special dye). Joint fluid added to a substance that promotes the growth of germs (such as bacteria or a fungus) may show an infection. This is called a culture.

What Affects the Test

You may not be able to have this test or the results may not be useful if:

  • You do not have enough fluid in the joint space.
  • You have recently had cortisone injected into the same joint.
  • You have an infection in the skin near the joint.

What To Think About

  • Your doctor may recommend further treatment with medicine, physiotherapy, or surgery after the cause of your joint pain has been found.
  • Tissue from the joint lining may be removed during this test (synovial biopsy). The tissue sample is then examined under a microscope.


Other Works Consulted

  • Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.


Current as of:
August 5, 2020

Author: Healthwise Staff
Medical Review:
Anne C. Poinier MD - Internal Medicine
Brian D. O'Brien MD - Internal Medicine
E. Gregory Thompson MD - Internal Medicine
Adam Husney MD - Family Medicine
Martin J. Gabica MD - Family Medicine
Kathleen Romito MD - Family Medicine