Making the Diagnosis
Using a number of tests, a doctor is able to diagnose psoriatic arthritis and eliminate other possible conditions. Often, the skin symptoms of psoriasis (present or past) are clear indicators. Pitting of the fingernails is an almost certain sign that joint pain is caused by psoriatic arthritis and not some other form of arthritis.
The first step is to X-ray the joints to see what changes are taking place. Next, a doctor may do a blood test for rheumatoid factor to eliminate the possibility of rheumatoid arthritis. Tests of fluid in the joints can also rule out gout, which may have arthritic symptoms very similar to psoriatic arthritis. This process of elimination is necessary because there's no test that confirms a diagnosis of psoriasis or psoriatic arthritis. That's why diagnosis of psoriatic arthritis is usually based on the characteristic presence of both skin and joint symptoms.