your doctor will diagnose psoriatic arthritis based on a physical exam patient history family history and lab tests. while there is no specific lab test to diagnose psoriatic arthritis blood tests from some patients may reveal mild anemia and elevated erythrocyte sedimentation rate. erythrocyte sedimentation rate (sed rate or esr) is a test that gives a rough index of inflammation. the sed rate is not specific and can be elevated with many other conditions such as other autoimmune syndromes infection tumor liver disease or pregnancy. your doctor may do other blood tests such as rheumatoid factor to help exclude the diagnosis of rheumatoid arthritis. rheumatoid factor is a blood test that is positive in 70% to 80% of those with rheumatoid arthritis. however this test may be positive in healthy people and negative in people with rheumatoid arthritis so it is not conclusive. when one or two large joints (such as knees) are inflamed arthrocentesis can be performed. arthrocentesis is an office procedure in which a sterile needle is used to withdraw (aspirate) fluid from the inflamed joints. the fluid is then analyzed for infection gout crystals and other inflammatory conditions. x-rays may show changes of cartilage or bone injury indicative of arthritis of the spine sacroiliac joints and/or joints of the hands. typical x-ray findings include bony erosions resulting from arthritis. magnetic resonance imaging tests (mri) may also be used to detect joint and tissue inflammation. the blood test for the genetic marker hla-b27 can be found in more than 50% of patients with psoriatic arthritis who have spine inflammation. because psoriatic arthritis may lead to bone loss a bone density scan may be taken to measure bone strength and to assess which patients may be at risk for osteoporosis and fractures.
how is psoriatic arthritis diagnosed?