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What Is Arthritis?

Arthritis describes a group of conditions in which inflammation or disease affects one or more joints. Arthritis can affect any joint in the body but is most common in weight-bearing joints such as the spine, knee, and hip. Arthritis may involve one joint (monoarthritis) or more than one joints (oligoarthritis or polyarthritis).

Arthritis is the leading cause of disability in the United States, affecting approximately 54.4 million adults. This group of conditions can be related to several underlying causes, such as:

  • Gradual wear and tear on the joints
  • An autoimmune disorder in which the immune system attacks otherwise healthy cells
  • An injury, such as a fracture or broken bone
  • Infection, often with a virus or bacteria
  • The buildup of crystals in and around the joint, including those formed of uric acid and calcium pyrophosphate dihydrate

In patients with arthritis, a joint becomes inflamed, which leads to swelling, stiffness, and pain. If left untreated, inflammation can cause long term or permanent disability. There are over 100 different types of arthritis. The most common types of arthritis include:

  • Osteoarthritis: Osteoarthritis is the most commonly diagnosed form of arthritis. Frequently affecting the hips, knees, and hands, osteoarthritis develops when the cartilage within a joint starts to break down.
  • Rheumatoid arthritis: Rheumatoid arthritis is an autoimmune disorder in which a person’s immune system attacks healthy cells, causing inflammation, pain, and swelling in the affected joints or other organs.
  • Gout: Gout is associated with excess uric acid in the body that forms needle-like crystals in affected joints, fluids, and other tissues. Episodes, called flares, of gout can start suddenly and may last for days or weeks.
  • Ankylosing spondylitis: A chronic form of arthritis, ankylosing spondylitis mainly affects the spine, causing painful inflammation of the joints between the vertebrae and between the spine and pelvis. As the disease progresses, it can sometimes cause the bones in the spine to fuse together.
  • Fibromyalgia: Fibromyalgia is a type of arthritis that is characterized by full-body pain and stiffness, fatigue, and other symptoms.
  • Lupus: People with lupus experience symptom flares and periods without symptoms called remission. When symptoms occur, joint pain and swelling are common.
  • Psoriatic Arthritis: This type of arthritis occurs in some people who have a skin condition called psoriasis. Psoriatic arthritis is marked by painful, swollen, and stiff joints as well as other symptoms.

Other types of arthritis include juvenile rheumatoid arthritis, a diverse condition that first appears in children younger than 16 years of age, septic arthritis, and reactive arthritis. Septic arthritis is caused by an infection in a joint, while reactive arthritis develops in response to an infection in another part of the body.

The Role of Arthritis Testing

Arthritis testing may be used for diagnosis, guiding treatment, or monitoring of arthritis: 

  • Diagnosis: Arthritis testing is often used to diagnose the cause of a person’s symptoms and rule out other health conditions.
  • Treatment planning: In some patients, arthritis testing is used to plan for treatment or determine a patient’s risk of severe side effects while receiving arthritis treatment.
  • Monitoring: While patients are being treated for arthritis, testing may be used to monitor the effectiveness of medications and track the progression of the disease.

Who should get testing?

Anyone with concerns about arthritis should talk to their doctor about whether or not arthritis testing is appropriate. Arthritis testing may be recommended for patients experiencing symptoms of arthritis in one or multiple joints. In patients with symptoms in a single joint, indications for urgent arthritis testing include:

  • Joint pain, swelling, warmth, or stiffness
  • Fever
  • Skin changes near the joint, including broken, red, warm, or tender skin
  • Past diagnosis of a severe bleeding disorder
  • Past diagnosis or current symptoms of a sexually transmitted disease

In patients with symptoms affecting multiple joints, indications for seeking prompt medical care, including arthritis testing, include:

  • Joint changes, including swelling, warmth, and redness
  • Skin changes, including rashes, spots, or blotches
  • Sores, especially in the mouth, nose, or near the genitals
  • Chest or abdominal pain
  • Shortness of breath or severe cough
  • Fever, sweats, weight loss, or chills
  • Eye changes, including redness or pain

Arthritis testing is also performed in patients who have been diagnosed with certain types of arthritis in order to plan treatment, as well as monitor treatment progress and disease progression. In these cases, arthritis testing can aid doctors in managing the disease as effectively as possible.

Getting test results

There are many tests that are used in diagnosing and treating arthritis. The time it takes to receive test results depends on the type of test performed and whether or not test samples need to be sent to a specialized laboratory for analysis. While some test results may be available on the same day, other tests can take days or weeks to complete.

Testing results are often communicated to patients through a follow-up appointment, phone call, or online medical chart. Patients with questions about their test results, including when to expect results, should contact their doctor for more information.

It’s important to keep in mind that, although a single test can provide a lot of information, diagnosing and treating arthritis often depends on results of more than one test.

Types of Arthritis Tests

Diagnosing arthritis involves taking a patient’s medical history, conducting a physical examination, and performing imaging and blood tests. Testing of joint fluid (known as synovial fluid) is often needed. Because there are many types of arthritis, it’s important for doctors to identify the type(s) of arthritis causing a patient’s symptoms.

After taking a patient’s medical history and conducting a physical exam, doctors may recommend a synovial fluid analysis. Synovial fluid is located in the spaces between joints and cushions bone ends to reduce friction during movement of the joint. The synovial fluid analysis consists of a group of tests that determine the underlying cause of arthritis. For example, the presence of needle-shaped uric acid crystals helps confirm gouty arthritis.

Additional tests may be used to diagnose arthritis and rule out other conditions. The selection of tests depend on a patient’s symptoms and the type of arthritis suspected by doctors.

Several tests may be performed to determine whether a patient’s symptoms are related to inflammation, including from infectious or other systemic disorders. However, these tests are not able to identify the specific underlying cause:

Tests Related to Diagnosing Inflammatory Disorders
Test Name Test Sample What It Measures
White Blood Cell Count (WBC) Blood sample The amount of white blood cells in a blood sample
Erythrocyte Sedimentation Rate  (ESR) Blood sample How quickly red blood cells (known as erythrocytes) settle in a test tube
C-Reactive Protein (CRP) Blood sample A protein that increases due to inflammation in the body

Additional tests may be ordered to diagnose or rule out autoimmune rheumatic disorders, including rheumatoid arthritis and ankylosing spondylitis:

Tests Related to Diagnosing Autoimmune Rheumatic Disorders
Test Name Test Sample What It Measures
Antinuclear Antibody (ANA) Blood sample Autoantibodies (immune proteins) present in certain autoimmune disorders
Cyclic Citrullinated Peptide (CCP) Antibody Blood sample Anti-CCP antibodies present in certain autoimmune disorders, particularly in rheumatoid arthritis
Rheumatoid Factor (RF) Blood sample An autoantibody that is present in some autoimmune disorders
HLA-B27 Blood or urine sample Presence of the protein HLA-B27 on the surface of cells, which can increase risk for some autoimmune disorders, such as ankylosing spondylitis

Other tests may be performed to determine the cause of inflammation or blood detected in the synovial fluid or to rule out other causes of arthritis:

Tests Related to Diagnosing Other Causes of Arthritis
Test Name Test Sample What It Measures
Prothrombin Time and International Normalized Ratio (PT/INR) Blood sample How long it takes for a blood clot to form
Partial tissue thromboplastin time (PTT) Blood sample How long it takes for a blood clot to form
Platelet count Blood sample Number of platelets in a blood sample
Blood culture Blood sample The presence of microbes in the blood, including bacteria and other germs
Gonorrhea testing Urine sample or swab from site of potential infection The presence of the bacteria Neisseria gonorrhoeae in the body
Chlamydia testing Vaginal swab, rectal swab, or urine sample The presence of a chlamydia infection

Imaging tests may be needed to further evaluate abnormalities, but are often unnecessary when evaluating a patient with symptoms affecting the joints. When imaging tests are performed, they may include an x-ray, CT, MRI, or ultrasound.

Rarely, a biopsy of the bone, synovium, or other tissues may be used to rule out other causes of joint pain, such as certain types of infections and tumors.

When used in treatment planning, arthritis testing may involve genetic testing, which analyzes a patient’s DNA, to determine appropriate treatment. One type of genetic analysis, called HLA testing, may be ordered for patients of certain ethnic backgrounds who are diagnosed with gout. HLA testing in patients diagnosed with gout determines whether or not patients have a specific gene variant, called the HLA–B*5801 allele. If present, this gene variant puts these patients at a higher risk of severe side effects from medication used to treat gout.

Another example of genetic testing used in planning treatment for arthritis is in patients diagnosed with rheumatoid arthritis. Patients diagnosed with rheumatoid arthritis may be treated with a type of medication called thiopurine prodrugs. Testing for variants in the thiopurine methyltransferase (TPMT) and nudix hydrolase 15 (NUDT15) genes can help doctors understand the extent to which a patient’s body is able to metabolize thiopurine prodrugs. Understanding drug metabolism is helpful in determining safe and effective dosage of these medications.

Arthritis testing may also be used to monitor patients with many types of arthritis over time. For example, patients diagnosed with gout have levels of blood uric acid measured at regular intervals to monitor the effectiveness of gout treatment. Patients with rheumatoid arthritis may have many blood tests during treatment to monitor the progression of the disease and detect unexpected side effects or toxicity of treatment.

Getting Tested for Arthritis

Arthritis testing is ordered by a doctor or specialist if indicated by a patient’s signs or symptoms. For testing that requires a sample of a patient’s blood, the sample can be drawn in a doctor’s office or other medical setting.

A sample of synovial fluid is obtained through a procedure called a joint aspiration or arthrocentesis. During a joint aspiration, a doctor applies local anesthesia to the affected joint before using a needle to withdraw a sample of synovial fluid for analysis. An ultrasound may be performed during a joint aspiration to help the doctor obtain the sample.

Urine samples and oral swabs may be collected by a doctor or by the patient using a doctor’s instructions. In some cases, a 24-hour urine sample may be required, which involves the collection of all a patient’s urine over a 24-hour period.

At-home Arthritis testing

At-home testing does not diagnose arthritis and is not a substitute for either medical care or testing ordered by a doctor or specialist. However, at-home tests are available that analyze several substances related to arthritis:

  • At-home cyclic citrullinated peptide (CCP) antibody testing: At-home tests may be available that detect the presence of anti-CCP antibodies in the blood. This test involves obtaining a blood sample from the finger tip at home, collecting the sample in a test vial, then mailing the test vial into a laboratory for analysis.
  • At-home rheumatoid factor (RF) testing: At-home tests are available that measure rheumatoid factor in the blood. At-home rheumatoid factor testing requires users to obtain a blood sample using a finger stick, collect a blood sample in the test vial, then send the test vial into a laboratory.
  • At-home uric acid testing: Tests measuring levels of uric acid in the blood involve obtaining a drop of blood from a finger stick, applying it to a test strip, and reading the result on a handheld meter.
  • At-home gonorrhea testing: At-home gonorrhea testing involves collecting a sample of urine and mailing it to a certified laboratory using a prepaid shipping label.
  • At-home chlamydia testing Testing for chlamydia at home requires patients to collect a swab from a potential site of infection or a sample of urine and mail it to a laboratory for testing.

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