Also Known As
Joint fluid analysis
Formal Name
Synovial fluid analysis
This article was last reviewed on
This article waslast modified on 9 December 2019.
At a Glance
Why Get Tested?

To help diagnose the cause of joint inflammation, pain, and/or swelling

When To Get Tested?

When one or more of your joints are swollen, red, and/or painful

Sample Required?

A sample of synovial fluid is collected by a doctor from the affected joint with a syringe and needle using a procedure called a joint aspiration. The sample is called a joint aspirate.

Test Preparation Needed?

Consult with your doctor about test preparation. Synovial fluid collection and analysis may be performed after fasting or at random.

On average it takes 7 working days for the blood test results to come back from the hospital, depending on the exact tests requested. Some specialist test results may take longer, if samples have to be sent to a reference (specialist) laboratory. The X-ray & scan results may take longer. If you are registered to use the online services of your local practice, you may be able to access your results online. Your GP practice will be able to provide specific details.

If the doctor wants to see you about the result(s), you will be offered an appointment. If you are concerned about your test results, you will need to arrange an appointment with your doctor so that all relevant information including age, ethnicity, health history, signs and symptoms, laboratory and other procedures (radiology, endoscopy, etc.), can be considered.

Lab Tests Online-UK is an educational website designed to provide patients and carers with information on laboratory tests used in medical care. We are not a laboratory and are unable to comment on an individual's health and treatment.

Reference ranges are dependent on many factors, including patient age, sex, sample population, and test method, and numeric test results can have different meanings in different laboratories.

For these reasons, you will not find reference ranges for the majority of tests described on this web site. The lab report containing your test results should include the relevant reference range for your test(s). Please consult your doctor or the laboratory that performed the test(s) to obtain the reference range if you do not have the lab report.

For more information on reference ranges, please read Reference Ranges and What They Mean.

What is being tested?

Synovial fluid is a thick liquid that acts as a lubricant for the major joints of the body. It is found in small quantities in the spaces between the bones in a joint, called the synovial cavity. Here the fluid is produced and contained by the synovial membranes which cover the inner surface of the cavity. Synovial fluid lubricates the joint and reduces friction during movement in the knees, shoulders, hips, hands, and feet.

Synovial fluid analysis consists of inspection of fluid, as well as tests that detect changes in synovial fluid that may indicate the presence of diseases that affect joint structure and function.

Accordion Title
Common Questions
  • How is it used?

    Synovial fluid analysis may be requested to help diagnose the cause of joint inflammation, pain, swelling, and fluid accumulation. Diseases and conditions affecting one or more joints and the synovial fluid can be divided into four main categories:

    Infectious diseases: those caused by bacteria, fungi, or viruses. They may originate in the joint or spread there from other places in the body. These conditions include acute and chronic septic arthritis.

    Bleeding: bleeding disorders and/or joint injury can lead to bleeding in the synovial cavity. Commonly present in patients with untreated blood clotting disorders such as haemophilia or von Willebrand Disease.

    Inflammatory diseases including:

    Conditions that cause crystal formation and accumulation such as gout (needle-like uric acid crystals) and pseudogout (calcium pyrophosphate dihydrate crystals). Typically these affect the feet and legs. The diagnosis of gout is usually supplemented by measuring uric acid in blood.

    Conditions that cause immune mediated joint inflammation including autoimmune disorders such as rheumatoid arthritis and systemic lupus erythematosus (SLE). Other disorders such as sarcoidosis, Crohn’s disease and ulcerative colitis may be associated with arthritis. Infections in other parts of the body may produce a “reactive” arthritis also known as Reiter’s syndrome.

    Degenerative diseases such as osteoarthritis.

  • When is it requested?

    Synovial fluid analysis may be requested when a doctor suspects that a patient has a condition involving one or more of their joints and some of the following signs and symptoms:

    • Joint pain
    • Redness over the joint
    • Joint inflammation and swelling
    • Synovial fluid accumulation

    It is sometimes requested to monitor a patient with a known joint condition.

  • What does the test result mean?

    Synovial fluid aspirates usually contain a small amount of glucose and protein and may have a few white blood cells (WBCs) and red blood cells (RBCs).

    There are a wide variety of joint abnormalities including osteoarthritis, rheumatoid arthritis, gout, and infection (septic arthritis) that can cause inflammation, swelling, an accumulation of synovial fluid, and sometimes bleeding into one or more joints. These conditions can limit mobility and, if left untreated, may permanently damage the joints.

    The normal appearance of a sample of synovial fluid is usually:

    • Straw coloured
    • Clear
    • Viscous (thick) – drops of it from a syringe needle will form a “string” a few inches long.

    Changes in the physical characteristics may provide clues to the disease present such as:

    • Less viscous fluid may be seen in the presence of inflammation.
    • Cloudy synovial fluid may indicate the presence of microorganisms, white blood cells, or crystals.
    • Reddish synovial fluid may indicate the presence of blood, but an increased number of red blood cells may also be present in cloudy synovial fluid.

    The tests most commonly performed on synovial fluid are to look for microorganisms when infection is suspected. These include:

    • Gram stain allows the direct observation of bacteria or fungi under a microscope. There should be no organisms present in synovial fluid.
    • Culture and sensitivity is used to determine what type of microorganism is present. If bacteria are present, antibiotic sensitivity testing can be performed to guide antimicrobial therapy. If there are no microorganisms present, it does not rule out an infection; they may be present in small numbers or their growth may be inhibited because of prior antibiotic therapy.

    In addition:

    • Synovial fluid may be evaluated under polarised light to identify the presence of crystals and to distinguish the types of crystals, if present. Long needle-like monosodium urate crystals are associated with gout and short broader calcium pyrophosphate crystals are associated with pseudogout.
  • Is there anything else I should know?

    Other laboratory investigations which may be requested if a doctor suspects that a patient may have a systemic infection, include a full blood count (FBC), C reactive protein (CRP), and erythrocyte sedimentation rate (ESR). If gout is suspected, the doctor will request serum uric acid or urate. Some infections such as Lyme Disease (Borreliosis) are not easily diagnosed by joint aspirate and may require a specific blood test.

    Joint injury, surgery, and joint replacement can increase the risk of developing an infection in a joint.

  • What is arthrocentesis and how is it performed?

    Arthrocentesis is the removal of synovial fluid from a joint with a needle and syringe. A local anaesthetic is applied and then the doctor inserts the needle into the space between the bones and collects the synovial fluid.

  • Are there other reasons to do an arthrocentesis?

    Yes. Sometimes it will be performed to drain excess synovial fluid to relieve pressure in the joint and/or to aid in the treatment of an infection. Sometimes medicines such as corticosteroids will be introduced into the joint to help reduce inflammation and/or to relieve pain.