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What Is Psoriatic Arthritis?

Psoriatic arthritis (PsA) is a chronic disease that typically affects both the skin and the joints. Psoriasis is a skin disorder that causes patches of inflammation and thickening. Although many people with psoriasis do not have arthritis, nearly one in three will eventually experience joint problems. 

Psoriatic arthritis is an autoimmune disease. Symptoms occur when your immune system attacks tissues in your skin and in and around your joints. If you have a family history of autoimmune disease, you are more likely to develop psoriatic arthritis. It may also be associated with infections, injury, alcoholism, smoking, and obesity. 

Sometimes the symptoms will affect different parts of the body, and some people have episodes in which symptoms flare up and then improve. Although there is no cure for psoriatic arthritis, there are treatments that can relieve symptoms and slow the progression of the disease.

The Role of Psoriatic Arthritis Tests

Psoriatic arthritis testing is used to help diagnose the disease, to evaluate your suitability for certain treatments, and to monitor for treatment effects. 

No single test can diagnose or rule out psoriatic arthritis. This disease is diagnosed by a physician who uses a range of information, including: 

  • Family and medical history
  • Physical examination
  • Lab tests
  • Imaging tests like x-rays and MRIs
  • Analysis of synovial fluid in the joints

The symptoms of psoriatic arthritis are similar to those of several other diseases, such as rheumatoid arthritis, gout, and osteoarthritis. Your doctor will perform lab tests to rule out other diseases as the source of your symptoms. Excluding other disorders that cause similar symptoms is an important part of diagnosing psoriatic arthritis. 

Who should get testing?

Psoriatic arthritis should be considered when someone with psoriasis develops joint problems, especially when certain symptoms are present. 

Often, people who have psoriasis will be screened for psoriatic arthritis in order to detect the disorder early if it begins to develop. A variety of screening tools can be used, which may be administered by a primary care provider or dermatologist. Screening questionnaires ask about common features of psoriatic arthritis, such as: 

  • Swollen joints
  • Fingernail problems
  • Heel pain
  • Swollen fingers or toes

If you have symptoms of psoriatic arthritis, it is a good idea to discuss your concerns with your doctor. Early diagnosis and treatment can help prevent the severe joint damage that may occur if the disease progresses. 

Getting test results

Lab tests alone cannot diagnose psoriatic arthritis. Because of this, you will need to speak with your doctor about what your lab tests mean in combination with other medical findings.

Types of Psoriatic Arthritis Tests

If your doctor suspects you may have psoriatic arthritis, a number of tests may be used to help diagnose psoriatic arthritis and rule out other conditions. Several tests are designed to detect antibodies, which are proteins that help coordinate immune responses. The table below lists tests that are often used during the process of diagnosing psoriatic arthritis:

Tests Related to Diagnosing Psoriatic Arthritis (PsA)
Test Name Test Sample What It Measures Significance for PsA
Erythrocyte Sedimentation Rate (ESR) Blood sample How fast red blood cells settle in a test tube A measure of inflammation, ESR is higher than normal in approximately 40% of patients with PsA.
Rheumatoid Factor (RF) Blood sample An antibody found in autoimmune disorders Usually negative in PsA; positive result may indicate rheumatoid arthritis
Cyclic Citrullinated Peptide (CCP) Antibody Blood sample An antibody often found in rheumatoid arthritis Usually negative in PsA; positive result may indicate rheumatoid arthritis
HLA-B27  Blood sample Human leukocyte antigen  (HLA) B27 on the surface of cells Genetic marker associated with PsA
Antinuclear Antibody (ANA) Blood sample Autoantibodies present in some autoimmune disorders Present in a minority of patients with PsA; positive result may indicate other autoimmune diseases
C-Reactive Protein (CRP) Blood sample A protein made by the liver related to inflammation in the body Typically higher than normal in PsA
Immunoglobulin A Blood sample An antibody made by the immune system Higher than normal in most patients with PsA
Synovial Fluid Analysis Synovial (joint) fluid sample Chemical and microscopic aspects of joint fluid Very high white blood cell counts are typical in PsA.
Complete blood count (CBC) with differential Blood sample Levels of various blood components High white blood cell count and low red blood cell count (anemia) may be present in PsA.
Blood Urea Nitrogen (BUN) Blood sample Urea, a waste product of protein metabolism Frequently higher than normal in PsA
Creatinine Blood or urine sample Creatinine, a waste product removed by the kidneys Often increased in PsA
Uric Acid Blood or urine sample Uric acid, a waste product removed by the kidneys Commonly higher than normal in PsA
Urinalysis Urine sample Detects and measures a number of substances in urine Excess protein in the urine is common in PsA. 

Imaging tests are commonly used in the diagnosis of psoriatic arthritis. They can detect certain types of joint damage and deformity that are more common in psoriatic arthritis than in other joint diseases. X-rays are most typically used, but other tests like MRIs and CT scans may also be ordered.

Many doctors use the Classification of Psoriatic Arthritis (CASPAR) criteria to make a diagnosis of psoriatic arthritis. This tool takes into account many typical features of psoriatic arthritis, such as skin psoriasis, nail lesions, swelling of the fingers or toes, a negative rheumatoid factor (RF) test, and new bone formation seen on imaging tests. 

If psoriatic arthritis is diagnosed, your doctor may order additional lab tests before you begin treatment. Health issues such as heart disease, kidney or liver abnormalities, or infections may be taken into consideration when your treatment is planned. Sometimes, infections will be treated before treatment begins.  

Getting Tested for Psoriatic Arthritis

Testing for psoriatic arthritis is ordered by your doctor or a specialist, such as a rheumatologist, a doctor who specializes in joint diseases, or a dermatologist, a doctor whose specialty is treating the skin. Blood and urine specimens used in testing can be provided in a doctor’s office or laboratory. 

Synovial fluid analysis involves collecting a small amount of joint fluid using a process called arthrocentesis. During this procedure, a needle is used to withdraw fluid from the space around a joint. It is usually done at a doctor’s office. 

Some diagnostic imaging tests, like x-rays, may be done in a doctor’s office. Others may need to be performed at an imaging center or hospital radiology department. 

At-home testing

Some of the tests used to diagnose and manage psoriatic arthritis are available as at-home tests. However, it is very important to work closely with a doctor if psoriatic arthritis is suspected. Psoriatic arthritis is a diagnosis made based on a doctor’s evaluation of many factors, not on the basis of a single test, so at-home testing alone is of limited benefit. 

You can speak with your doctor about whether at-home testing can play any role in your case. 

For some tests, testing kits enable you to obtain a blood sample using a finger prick. The sample is then mailed to a laboratory for analysis, and results are available through a secure online portal. The following tests are available with this type of at-home kit: 

  • At-home rheumatoid factor (RF) testing
  • At-home cyclic citrullinated peptide (CCP) antibody testing
  • At-home C-reactive protein testing

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