Psoriatic arthritis is a chronic form of arthritis. People may need multiple medical tests, including blood tests and imaging scans, to help diagnose psoriatic arthritis and show how the condition is progressing.

Psoriatic arthritis (PsA) is an autoimmune condition that causes joint swelling, stiffness, and pain. It can also cause enthesitis, which refers to inflammation and pain in bodily areas where ligaments and tendons attach to bones.

No single test can diagnose PsA. Typically, a doctor will request multiple tests to check for signs of PsA and rule out other conditions.

This article outlines 12 medical tests doctors may use to diagnose and monitor PsA.

There is no definitive diagnostic test for PsA, so doctors assess a person’s symptoms to help with diagnosis.

According to the National Psoriasis Foundation, 85% of people with PsA experience skin symptoms first, such as a scaly rash and nail pitting. Doctors may diagnose the condition if someone has these symptoms alongside joint swelling, stiffness, and tenderness.

Diagnostic ultrasound is an imaging test that uses sound waves to create pictures of the inside of the body. It is particularly useful for viewing soft tissues, such as tendons, ligaments, and the synovium membrane that lines joints.

An ultrasound may help diagnose PsA if someone develops symptoms of joint inflammation or enthesitis. Doctors may also use ultrasound to monitor someone with psoriasis for early signs of PsA, even if the person has not yet developed enthesitis.

An X-ray is a type of imaging test for examining bones. Doctors may use them to check for bone changes resulting from PsA or other types of arthritis.

Different types of arthritis may affect the bones in different ways. Identifying certain types of changes can help determine the type of arthritis a person has.

X-rays can help doctors diagnose PsA and monitor the condition following diagnosis and treatment. A person may need regular follow-up X-rays or when new symptoms develop.

Early signs of PsA may not show up on an X-ray.

A CT scan combines multiple X-ray images to create cross-sectional pictures of the bones. It is particularly useful for examining bones in complex joints or areas that may be difficult to see on a standard X-ray.

For example, a healthcare professional may use a CT scan to examine the shoulder girdle, spine, pelvis, or sacroiliac joints. It may also help diagnose PsA.

A person may need follow-up scans to monitor the condition following diagnosis and treatment.

MRI scans use magnetic and radiofrequency fields to create 3D pictures of the inside of the body. It can provide more detailed pictures than an X-ray.

An MRI may help doctors diagnose PsA. Follow-up MRIs can help monitor the condition following diagnosis and treatment.

Early signs of PsA are more likely to show up on an MRI than an X-ray.

If someone has skin or nail symptoms and joint symptoms, a doctor may request a skin or nail biopsy to examine the affected skin or nail.

During the biopsy, a healthcare professional will remove a small piece of the affected skin or nail. They will then examine the sample under a microscope for signs of psoriasis.

The ESR test measures how quickly red blood cells separate from other blood cells and settle to the bottom of a blood sample. A high ESR rate is a sign of inflammation, which can have various causes, including PsA, rheumatoid arthritis, or an infection.

An ESR test can help doctors confirm a diagnosis of PsA. A person often requires follow-up tests to monitor the condition after diagnosis and treatment. This can help determine whether the treatment is reducing inflammation.

CRP is a protein that the liver produces. High CRP levels are a sign of inflammation.

A CRP test can help confirm a diagnosis of PsA and monitor the condition during treatment. Frequent CRP tests can also help determine how well treatment is working.

High CRP levels may result from PsA or another condition that causes inflammation. It is also possible to have PsA with typical CRP levels.

RF is a protein that the immune system produces. Some people with PsA have high levels of RF, but this is more often a sign of rheumatoid arthritis.

Ruling out rheumatoid arthritis as a potential cause of joint symptoms is crucial when diagnosing PsA. An RF blood test can help with this.

Cyclic citrullinated peptide (CCP) antibodies are proteins in the blood of 60–80% of people with rheumatoid arthritis. These antibodies are less likely to be detectable in the blood of those with PsA.

An anti-CCP antibody blood test can help diagnose PsA or rule out rheumatoid arthritis as a potential cause of someone’s symptoms.

ANAs are proteins that attack the body’s tissues. The presence of ANA in the blood may indicate an autoimmune condition, such as lupus or other similar connective tissue diseases.

A positive ANA blood test may also indicate PsA.

Human leukocyte antigen (HLA) genes tell the body how to produce HLA proteins. These proteins are present on the surface of white blood cells. They help the immune system recognize the body’s own cells.

Some people inherit a copy of the HLA-B27 gene, which increases the risk of certain autoimmune conditions, such as PsA and ankylosing spondylitis.

An HLA-B27 antigen blood test can check for HLA-B27 protein in the blood. People with this protein have an increased risk of PsA.

However, not everyone with this protein will develop PsA, and not all those with PsA have this protein. Doctors often consider the results of an HLA-B27 antigen test in relation to a person’s medical history and other test results.

A doctor may perform a joint fluid analysis to check for signs of certain conditions that can affect the joints, such as:

  • PsA and other types of inflammatory arthritis
  • joint infections
  • gout

Healthcare professionals may also use a joint fluid analysis to help rule out gout and joint infections as potential causes of a person’s symptoms.

Gout is a type of arthritis that develops when uric acid crystals build up in the joints. It can cause symptoms similar to PsA.

In this test, a healthcare professional will insert a needle into an affected joint to draw out a sample of joint fluid. They will send this sample to a laboratory, where a technician will analyze it for inflammatory markers, uric acid crystals, and other irregularities.

A person often needs multiple tests for a doctor to diagnose PsA and rule out other potential causes of symptoms. The doctor will also consider the individual’s medical history and physical exam when reviewing test results.

As many people with PsA experience skin and nail changes first, doctors usually ask about these and examine the skin and nails. Imaging scans and blood tests are also important in confirming a PsA diagnosis.