Psoriatic arthritis is a chronic form of arthritis. Multiple medical tests, including blood tests and imaging scans, are often needed 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, or inflammation and pain at sites where ligaments and tendons attach to bones.
Many people with PsA also have a history of psoriasis, which can cause skin and nail symptoms. These symptoms include a scaly rash and nail pitting.
PsA can cause similar symptoms as other types of arthritis, such as rheumatoid arthritis, ankylosing spondylitis, and gout. Other autoimmune conditions, joint infections, or injuries may also cause similar symptoms.
No single test can diagnose PsA. Typically a doctor will request multiple tests to check for signs of PsA and rule out other conditions. They will also rely on a person’s medical history and a physical exam.
Healthcare professionals will also perform follow-up tests after diagnosis to learn how the condition is progressing or responding to treatment.
Read on to learn about 12 medical tests that doctors may use to diagnose and monitor PsA.
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.
It may also be used to monitor someone with psoriasis for early signs of PsA, even if the person has not yet developed joint symptoms or enthesitis. The individual may need additional imaging and blood tests if the ultrasound shows signs of inflammation or damage.
An X-ray is a type of imaging test used for examining bones. Doctors may use X-rays to check for bone changes that can result 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 follow-up X-rays regularly or when new symptoms develop.
Early signs of PsA may not show up on an X-ray.
A computed tomography (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.
Magnetic resonance imaging (MRI) uses magnetic and radiofrequency fields to create 3D pictures of the inside of the body. It is useful for examining both soft tissues and bones. 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 along with joint symptoms, a doctor may request a skin or nail biopsy to visually examine the affected skin or nail.
During the biopsy, a healthcare professional will remove a small piece of the affected skin or nail. It will then be examined under a microscope for signs of psoriasis.
According to the National Psoriasis Foundation, approximately 30% of people with psoriasis develop PsA, and most people with PsA have a history 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.
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.
In this test, a healthcare professional will insert a needle into a vein to draw a sample of blood, which they will then send to a laboratory for testing.
A high ESR level may be a sign of PsA or another condition that causes inflammation, such as rheumatoid arthritis, lupus, or an infection. It is also possible to have PsA with a typical ESR level.
It is crucial to consider a person’s medical history and other test results when interpreting the ESR results.
C-reactive protein (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.
A doctor will consider a person’s medical history and other test results when interpreting their CRP levels.
Rheumatoid factor (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 present in the blood of 60–80% of people with rheumatoid arthritis. These antibodies are less likely to be detectable in the blood of people with PsA.
An anti-CCP antibody blood test can help with the diagnosis of PsA or rule out rheumatoid arthritis as a potential cause of a person’s symptoms.
Antinuclear antibodies (ANA) are proteins that attack the body’s own tissues. The presence of ANA in the blood may be a sign of 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 all people with this protein develop PsA, and not all people 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
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 confirm a diagnosis of PsA and rule out other potential causes of symptoms. The doctor will also consider a person’s medical history and physical exam when reviewing test results.
Healthcare professionals often recommend a combination of medication, physical therapy, and lifestyle changes to treat PsA. Some medications are effective for treating both PsA and psoriasis.
A person may need additional tests before a doctor prescribes certain treatments. For example, biologics are not safe for people with tuberculosis. So, a doctor may request a blood test and chest X-ray to determine whether someone has tuberculosis before prescribing biologic medication.
In addition, a person often needs frequent follow-up tests to determine how well the PsA is responding to treatment. These may include ESR and CRP blood tests, imaging tests, or other tests to check for signs of inflammation and bone damage.
Some treatments for PsA may cause anemia, liver damage, or other side effects. Complete blood counts (CBC), liver enzyme tests, or other tests are often used to check for and monitor side effects.