12 Medical Tests for Psoriatic Arthritis, Explained

Few people like being poked and prodded, but if you’re living with psoriatic arthritis (PsA), regular medical testing is vital to keeping healthy. Psoriatic arthritis tests not only help your doctor diagnose this autoimmune condition but are also important for monitoring the disease’s progression, as well as managing psoriatic arthritis symptoms like painful joint inflammation.

Diagnosing psoriatic arthritis can be challenging because there’s no single test, says Magdalena Cadet, MD, a clinical rheumatologist and adjunct assistant professor in the department of medicine at New York University's Grossman School of Medicine in New York City. Along with a physical exam, you’ll likely need a series of both imaging procedures and blood tests in order to make a psoriatic arthritis diagnosis, as well as rule out other forms of arthritis, such as rheumatoid arthritis or gout. “Many types of arthritis are associated with inflammation, and it’s important to distinguish between them in order to initiate a treatment plan,” Dr. Cadet says.

The tests can help detect conditions associated with psoriatic arthritis, too, such as heart disease. “A physician may also closely monitor your blood pressure or cholesterol levels to assess cardiac risk factors,” Cadet says.

Here are 12 key medical tests that can help detect and monitor psoriatic arthritis.

1. X-Ray

X-rays, which use low-dose radiation to produce images of the inside of the body, can help your doctor make a psoriatic arthritis diagnosis and monitor progression of PsA.

“X-rays allow the doctor to see changes to the bone,” says Elyse Rubenstein, MD, a rheumatologist in Santa Monica, California. In people with psoriatic arthritis, X-rays may show bone erosion, new bone formation, bone fusion, or a phenomenon called “pencil in cup,” in which the ends of the bone have been eroded to a pencil-like point. Any of these changes indicate that the disease is getting worse, Dr. Rubenstein says.

Frequency of Testing A doctor may take an initial X-ray to help diagnose psoriatic arthritis and rule out other forms of arthritis that have different patterns of joint involvement, says Rubenstein.

After that, how often you have X-rays depends on your physician and the state of your disease. Some doctors take X-rays just once a year for routine monitoring, while others may take them only when a patient’s condition changes.

2. MRI

This noninvasive imaging technique uses a magnetic field and computer-generated radio waves to create detailed three-dimensional images.

A radiologist analyzes the MRI, then reports back to the rheumatologist. Inflammation, swelling, and bone erosion all indicate that psoriatic arthritis is active, notes Rubenstein.

Frequency of Testing A doctor may order an MRI during initial testing to help with making a psoriatic arthritis diagnosis, as well as later to monitor the disease or look for any changes in a patient’s psoriatic arthritis symptoms.

3. Erythrocyte Sedimentation Rate

Erythrocyte sedimentation rate, or ESR or sed rate, is a blood test that measures inflammation in the body, which helps determine a psoriatic arthritis diagnosis, says Elaine Husni, MD, MPH, vice chair of rheumatology and director of the Arthritis and Musculoskeletal Center at the Cleveland Clinic.

As with many blood tests, labs each have their own, slightly different reading of what ESR numbers mean, which they interpret based on past results, says Cadet. Age is also a factor. “ESR can be elevated slightly in elderly patients and still be normal for that person,” she says.

Frequency of Testing In addition to diagnosis, testing may be done several times a year to determine if there’s ongoing inflammation, says Cadet.

4. C-Reactive Protein

C-reactive protein (CRP) is a protein in the blood that indicates inflammation. If a blood test shows high CRP levels, you might have psoriatic arthritis, says Dr. Husni.

“Your doctor may use the test if your ESR is normal, since CRP is more accurate at detecting inflammation in some people,” adds Cadet.

Again, different labs may have slightly different interpretations of readings.

Frequency of Testing CRP analysis may be done for diagnosis and then several times a year to assess whether inflammation has responded to treatment, notes Cadet.

5. Rheumatoid Factor

Rheumatoid factor (RF), a protein produced by the immune system that can be a marker for autoimmune dysfunction, is sometimes an indication of systemic inflammation.

Although RF is mostly associated with rheumatoid arthritis, it can also occur in a small percentage of people with psoriatic arthritis, says Rubenstein. To distinguish the two conditions, doctors will look at RF levels in the context of other factors, such as a certain pattern of joint involvement and symptoms of psoriasis, which can accompany psoriatic arthritis.

Frequency of Testing This is usually done only at the initial diagnostic appointment, says Rubenstein.

6. Anti-Cyclic Citrullinated Peptide Test

Blood tests that look for the presence of anti-cylic citrullinated peptide antibodies (anti-CCPs), which are inflammatory, are commonly used to diagnose rheumatoid arthritis, but anti-CCPs can also indicate psoriatic arthritis.

Frequency of Testing The anti-CCP test is typically done in a patient’s initial evaluation.

7. HLA-B27

HLA-B27 is a blood test that looks for a genetic marker for psoriatic arthritis — a protein called human leukocyte antigen B27 (HLA-B27), which is located on the surface of white blood cells.

HLA-B27 is associated with a larger group of autoimmune diseases, called spondyloarthropathies, which includes psoriatic arthritis, Cadet says. These conditions can cause inflammation in the entheses anywhere in the body, but mainly in the spine.

If untreated over a long period, this inflammation may cause the destruction of cartilage, muscle spasms, and a decrease in bone mineral density that may lead to osteopenia or osteoporosis.

Frequency of Testing “The HLA-B27 test is usually performed only at an initial visit to help establish a diagnosis,” says Cadet.

8. Tuberculosis Test

Tuberculosis (TB) is a bacterial infection that typically affects the lungs but can also reach bones, joints, and kidneys. Symptoms include fever, night sweats, chills, coughing, weight loss, and fatigue.

People with psoriatic arthritis must have a negative TB test before they can take biologic medications, which are protein-based drugs given by injection or infusion. By suppressing the immune system, these medications may reactivate latent (inactive) tuberculosis.

A TB blood test assesses whether the body has launched an immune response to the presence of Mycobacterium tuberculosis bacteria. The test is done in a lab after a blood sample is drawn.

Frequency of Testing Doctors order a TB test before prescribing biologics and may repeat testing annually as long as a patient is taking the medication, says Cadet. She adds, “Any patient who exhibits symptoms or has been exposed to TB should have an immediate TB test.”

9. Chest X-Ray

Doctors often order a chest X-ray in conjunction with a TB test to increase the chance of detecting infection, says Cadet. “The X-ray may show scarring from prior exposure to TB, or if there’s an active or new infection,” she says.

Frequency of Testing As with the TB skin test, doctors may order a chest X-ray prior to prescribing biologics, repeating the test annually as long as the patient is taking the medication, says Cadet.

10. Serum Uric Acid

Frequency of Testing Testing may be done several times a year, says Cadet.

11. Bone Mineral Density Scan

Unfortunately, common psoriatic arthritis medications — such as prednisone, a corticosteroid — can weaken bones over time and increase the risk of osteoporosis. “And psoriatic arthritis itself is associated with a decrease in bone mineral density,” notes Rubenstein.

If you’re diagnosed with osteopenia, a condition involving weakened bones that may lead to osteoporosis, your doctor will discuss medications that can slow or stop bone loss, and may recommend calcium and vitamin D supplements along with resistance exercise, says Rubenstein.

Frequency of Testing “Bone density screening is done during menopause and every one to two years after that,” says Rubenstein. “If a patient is on prednisone or other medications that decrease bone mineral density, the test may be done earlier and repeated every one to two years.”

12. Blood Test for Anemia

When you have psoriatic arthritis, ongoing inflammation may cause anemia, a decrease in healthy red blood cells that can lead to dizziness, shortness of breath, and exhaustion, says Cadet.

If blood work reveals anemia, your doctor will give you an exam and other blood tests to find the cause. In people with psoriatic arthritis, treatments that reduce inflammation also help with anemia, says Cadet.

Frequency of Testing Doctors may order tests to be done several times a year to see if the anemia has worsened or improved.

Additional reporting by Julia Califano.