Psoriatic arthritis (PsA) can develop at any age but most often starts between ages 30 and 50 in adults and around 11 or 12 in children. If you or your child have a history of psoriasis and are experiencing joint pain, swelling, stiffness, or back pain, schedule an appointment with your health care provider. If you have PsA, an early diagnosis can help prevent long-term joint damage.

Although no single test can confirm a diagnosis of PsA, dermatologists and rheumatologists can review the results of several tests to look for signs of PsA, determine the type and how severe it is, and recommend effective treatment options.

Psoriatic Arthritis and Psoriasis

PsA is a long-term inflammatory disease that causes joint pain, swelling, and stiffness. Up to 30 percent of people with psoriasis may develop PsA as well. PsA is diagnosed using a range of clinical tools, including medical history, physical examination, blood tests, and imaging studies. In some cases, doctors may also take a biopsy of synovial fluid — the thick, slippery liquid in joints that reduces friction and cushions movement — from inflamed joints.

In nearly 80 percent of people with PsA, psoriasis appears before joint symptoms begin. PsA symptoms can look similar to other types of inflammatory arthritis, like rheumatoid arthritis, ankylosing spondylitis, and gout — a form of arthritis that causes sudden joint pain, swelling, and redness. Because of these similarities, people are sometimes misdiagnosed. An article in Rheumatology and Therapy found that PsA affects men and women equally.

Medical History and Examination

Rheumatologists typically diagnose and treat PsA. They start by taking a medical history. Approximately 40 percent of people with PsA have at least one close family member with psoriasis or PsA, so your health care provider will likely ask if anyone in your family has psoriasis or another autoimmune disease. If you’re not sure, talk to your relatives before your appointment so you can provide that information.

A physical exam will follow to check your skin, nails, and joints for possible symptoms of PsA or psoriasis. Your doctor may ask when the symptoms first started, how often they appear, how severe they are, and any factors that make them better or worse.

Your physician may also check your hands and feet for PsA symptoms. Nail changes (pitting, crumbling, or ridging of fingernails and toenails, including separation from the nail bed) are an early sign of PsA. Your doctor will also look for swollen fingers or toes (dactylitis or “sausage digits”), enthesitis (pain and swelling of tendons and ligaments where they connect to bone), and other hallmark symptoms of PsA.

The physician will also evaluate the condition of your joints by lightly pressing on areas to check for pain, tenderness, swelling, and warmth. You may be asked to perform simple physical activities that show range of motion, stiffness, and overall mobility.

If you have back pain, fatigue, or any other potential PsA symptoms, tell your doctor during the physical exam. The more information you provide, the more likely it is you’ll get an accurate diagnosis.

What Tests Confirm Psoriatic Arthritis?

No single test or marker can say for sure if someone has PsA. However, your doctor can use a few different blood tests to measure inflammation levels and rule out other types of arthritis. ​If you have questions about blood tests for PsA, schedule an appointment with your health care provider.

C-Reactive Protein

This test measures amounts of C-reactive protein (CRP), a molecule made by the liver and released into the bloodstream to strengthen the immune system. High CRP levels indicate inflammation. A CRP test cannot confirm a PsA diagnosis on its own. However, when used alongside other blood tests and imaging studies, a CRP test can help your doctor make an accurate diagnosis by providing more information.

Erythrocyte Sedimentation Rate

An erythrocyte sedimentation rate (ESR) test detects levels of inflammation by measuring the rate at which red blood cells (erythrocytes) fall or settle in a tall, vertical tube. The more red blood cells collect at the bottom of the tube (sedimentation) in one hour, the higher the inflammation level. The presence of CRP and other antibodies in the blood causes these cells to settle faster. Like the CRP test, the ESR test alone doesn’t diagnose a specific illness, but it can be used alongside other tests to detect conditions that cause inflammation.

Rheumatoid Factor

This blood test is routinely used to diagnose or rule out rheumatoid arthritis. It measures levels of rheumatoid factor (RF), a protein that causes the immune system to mistakenly attack healthy tissues.

People with PsA are typically RF-negative, so a positive RF test result would suggest rheumatoid arthritis instead of PsA. However, low levels of RF may also be in the blood, indicating either rheumatoid arthritis or — rarely — both conditions.

Anti-Cyclic Citrullinated Peptide

Anti-cyclic citrullinated peptide (anti-CCP) is another type of protein that attacks healthy tissues in the body. An anti-CCP test is primarily used to diagnose or rule out RA.

Human Leukocyte Antigen B27

Human leukocyte antigen B27 (HLA-B27) is a gene associated with several autoimmune diseases. A blood test for this marker may be used to look for signs of PsA in people with a family history of the disease. It can also help diagnose a related inflammatory condition, ankylosing spondylitis. HLA-B27 isn’t a direct cause of PsA, but testing positive for the gene suggests a higher risk of active disease within the spine.

Imaging Tests for the Diagnosis of Psoriatic Arthritis

In addition to lab tests for PsA, diagnostic imaging is frequently used to confirm a PsA diagnosis. X-rays detect joint damage while MRI, ultrasound, or CT scans provide a closer look at soft tissue in the joints.

X-Rays

Standard X-rays are most effective at diagnosing later-stage PsA. They can detect severe bone changes — such as the “pencil-in-cup” phenomenon — that distinguish PsA from other rheumatic diseases. This classic symptom occurs when one end of a bone has eroded to a pencil-point shape at the joint. It’s typically a sign of severe joint damage that could require more aggressive treatment options.

Ultrasound

Ultrasound uses sound waves to capture images inside the body. This test has proven effective in detecting enthesitis, a hallmark symptom of PsA, even before a person experiences pain or tenderness where tendons attach to bone. This imaging test also helps tell synovial inflammation apart from other types of arthritis.

MRI

MRI uses large magnets and radio waves to create images of organs and structures inside the body, such as soft tissues that may be damaged by enthesitis or inflammation in the vertebral column or sacroiliac joints. Research shows that MRI scans are useful for evaluating active PsA.

Biopsies for the Diagnosis of Psoriatic Arthritis

To further explore a diagnosis of PsA, your doctor may want to study a sample of synovial fluid from an affected joint or take a skin sample to confirm psoriasis. If you’ve got psoriasis on the skin, it’s a strong sign that joint symptoms could be due to PsA.

Arthrocentesis

Arthrocentesis is a procedure used to rule out certain types of arthritis when making a diagnosis. Your doctor collects synovial fluid from your joints using a needle and syringe. The fluid is then examined for immune cells, like white blood cells, that cause inflammation.

The fluid may also be tested for uric acid levels, which can help detect gout. People with psoriatic disease have higher levels of serum uric acid and are at high risk for gout, which is caused by a buildup of uric acid crystals in foot joints.

Skin Biopsy

To confirm the presence of psoriasis and rule out other skin conditions, such as eczema, your doctor may perform a punch biopsy. They use a pencil-shaped device to remove a small tissue sample for examination under a microscope and then close the incision with a couple of stitches.

If you have questions about blood tests, imaging, biopsies, or how to test for PsA based on your symptoms, a doctor specializing in rheumatology can help.

Psoriatic Arthritis Classification Criteria

The Classification Criteria for Psoriatic Arthritis (CASPAR) are often used to define PsA in clinical trials. Many rheumatologists also rely on the criteria to make an accurate and conclusive PsA diagnosis. The CASPAR criteria require that a person already have some form of inflammatory arthritis and at least three points from the following list to be diagnosed with PsA:

• Active psoriasis — 2 points
• Family history of psoriatic disease — 1 point
• Nail psoriasis — 1 point
• Negative RF factor — 1 point
• Bone damage — 1 point
• Dactylitis — 1 point

What Is the Prognosis for Psoriatic Arthritis?

Although there is currently no cure for PsA, a growing range of treatments can help prevent the disease from spreading and destroying joints. Early diagnosis of PsA is important because permanent joint damage can occur within a couple of months after onset, with the number of affected joints increasing over time. Studies support early diagnosis and treatment to improve long-term outcomes.

Talk With Others Who Understand

On MyPsoriasisTeam, the social network for people with psoriasis and psoriatic arthritis, more than 131,000 members come together to ask questions, give advice, and share their stories with others who understand life with psoriatic arthritis.

Have you been diagnosed with psoriatic arthritis? What was your experience with getting a diagnosis? Share your thoughts in the comments below, or start a conversation by posting on your Activities page.