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.
Roughly 8 to 16 percent of people with psoriatic arthritis will test positive for anti-CCPs, says Rubenstein. Some research has found the presence of anti-CCP in up to 20 percent of people with PSA.
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 positivity has been reported in 14 to 40 percent of patients with axial PsA, a form of PsA that causes inflammatory back pain, and in less than 10 percent of patients with predominantly peripheral PsA, which involves the joints in your arms, legs, hands, and feet.
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.
There are two kinds of TB tests: a skin test and a blood test. The skin test involves injecting a small amount of a protein called tuberculin into the skin of the lower arm, then checking the area around 48 to 72 hours later to see if there has been a reaction. The result depends on the size of the raised, hard area or swelling.
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
Uric acid is a substance that forms when the body breaks down purines, which are found in human cells and many foods. Elevated blood levels of uric acid are sometimes identified in people with psoriatic arthritis and can also be linked to gout, heart disease, and high blood pressure, according to Cadet.
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.
By measuring your blood levels of hemoglobin (the pigmented, oxygen-carrying component of red blood cells), your doctor can determine if you have anemia. A normal reading is 12 to 16 grams of hemoglobin per deciliter of blood in women and 14 to 18 grams in men.
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.
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