What Are Psoriatic Arthritis Blood Tests?

There is no single blood test that can check for psoriatic arthritis (PsA), a chronic, inflammatory disease of the joints that can also cause a skin disorder called psoriasis. Your doctor will order a series of blood tests to check for different signs of psoriatic arthritis. This means diagnosis will take more than a single visit.

While you might be tempted to rely on your doctor to monitor your condition through blood tests, you may find it’s helpful to have a basic understanding of what is being tested and why. This way, you’ll know which questions to ask to get the best treatment possible.

Types of Blood Tests

The specific types of blood tests your doctor will order may vary. Only after reviewing the results of these tests together, along with your symptoms, will your doctor make a diagnosis.

When it comes to inflammatory illnesses like PsA, the tests are typically checking for signs of inflammation in your blood. Doctors call these “biomarkers” of inflammation.

Following are the common blood tests for arthritis:

• Antinuclear antibody test (ANA): This is a basic blood test that can tell whether your body’s white blood cells are making higher levels of antibodies. A positive ANA test doesn’t necessarily mean you have an autoimmune disorder.
• Erythrocyte sedimentation rate (ESR, also called sed rate): Sed rate checks for inflammation and can be used to track progression of inflammatory diseases. An increased sed rate may indicate inflammation, but it can also be due to other conditions.
• C-reactive protein (CRP): This general blood test checks for the C-reactive protein and indicates the presence or absence of inflammation. 
• Rheumatoid factor (RF): If your rheumatoid factor is high, it could mean you have an autoimmune disease like rheumatoid arthritis. About 80% of rheumatoid arthritis patients have the rheumatoid factor in their blood.
• Human leukocyte antigen B27 (HLA-B27): This checks for the HLA-B27 protein on your white blood cells, which can show increased activity in disease states.
• Serum uric acid measurement: This tests uric acid levels (waste products) found in your blood and determines how well your body produces and then removes uric acid. Uric acid is made when your body breaks down purines from foods. High uric acid levels could indicate a type of arthritis called gout.

Other Tests for Psoriatic Arthritis 

You will likely also be required to take the following tests for your diagnostic examination to be considered complete:

• Bone density scans can check for joint damage or bone loss and look for other conditions like osteoporosis (weak bones), osteopenia (weak bones not quite as severe as osteoporosis), and demineralized bones (loss of calcium in bones).
• Imaging tests like X-rays and MRIs (magnetic resonance imaging tests) are used to examine bones and joints in detail to see the level of damage or inflammation.

Treatment Procedures

Your primary care doctor will order blood work, sending the lab request to the closest or most convenient clinic covered under your insurance plan. Your doctor may also ask you to get an imaging test.

Due to the nature of these blood and imaging tests, all of them require in-person visits. Follow-ups, however, may be handled either in person or through telehealth appointments (by way of video or audio visits in your home), especially when reviewing test results, renewing prescriptions, or doing general check-ins after you have your diagnosis.

Your Appointment

On the day of your appointment, you will have a laboratory technician, such as a phlebotomist, nurse, or other trained medical professional, draw blood from your arm. This is the person who will label your vials and either test them on-site or send them to a laboratory for assessment. 

If the tests show markers of inflammation and you are experiencing other symptoms of psoriatic arthritis (like psoriasis flare-ups, including itchy, scaly skin, and joint pain), you will be referred to a specialist called a rheumatologist. 

Your rheumatologist is the best person to:

• Confirm your diagnosis after reviewing all test results and your medical history
• Direct you toward the best treatment depending on the severity of your psoriatic arthritis and whether the symptoms are mostly external (skin issues), internal (joint issues), or a combination of both.

How to Prepare

Getting blood work usually is straightforward, but there are a few steps you can take to make sure the experience goes as smoothly as possible. If you're allowed to drink water, keep yourself as hydrated as possible prior to the blood draw.

Some of the most common factors to consider before getting blood work include:

• Verifying if you need to fast (abstain from food or drink) for any of the tests ordered
• Reviewing with your physician your medications, including any vitamins, supplements, herbs, and drugs, in case they can affect test outcomes
• Thoroughly reading your patient care instructions
  
• If you struggle with medical, needle, or blood phobias, asking your doctor for advice on coping strategies and whether you can bring a support person to the clinic
• Asking questions or if there’s anything else you should be aware of before leaving your appointment
  

Unless you are told to do so, don’t make major dietary changes before getting blood work. Doing so could compromise the quality of the results, including by affecting comparisons between past and current results.

A Word From Verywell

If your doctor has suggested blood testing to see if you have psoriatic arthritis, you may be surprised to learn there is no single test for this inflammatory condition. Rather, there are several important tests to check for levels of inflammation and for certain proteins in your blood that may indicate PsA.

Getting blood work, as well as imaging tests, will help your doctor diagnose your condition and find the most effective treatments available.