There isn't a blood test for psoriatic arthritis in the way that people who may have rheumatoid arthritis can be tested for rheumatoid factor. However, your doctor may test for rheumatoid factor to help distinguish between these conditions, as well as doing other blood tests to look for inflammation. You may have an X-ray; this can show up particular features of the disease, although these changes usually only appear once you have had arthritis for a while.
Attribution: BUPA