Diagnosing psoriatic arthritis can be difficult as there is no specific lab test for this condition. First a doctor will analyze if the patient has signs of psoriasis. If joint pain and inflammation is associated with psoriasis, chances are, it is psoriatic arthritis. Doctors will also check for a family history of this condition. It tends to run in families. The next step is to eliminate other forms of arthritis like rheumatoid arthritis, tendonitis, osteoarthritis etc.

This can be done by a lab test which checks the blood for the antibody called rheumatoid factor. A negative result for rheumatoid factor indicates that this is not rheumatoid arthritis. About 50% of people with psoriatic arthritis show the presence of a genetic marker called HLA-B27. This could be an indicator of psoriatic arthritis. The erythrocyte sedimentation rate can also tell doctors about the occurrence of inflammation.

Sometimes, a small amount of fluid may be aspirated from inflamed joints and analyzed to rule out conditions like bacterial infections, gout etc. An X-ray will also help doctors to identify psoriatic arthritis. This condition is characterized by bone erosion, destruction and deformities. An X-ray will help doctors identify these problems and make a correct diagnosis.