Although the test for rheumatoid factor (RF) is helpful in rheumatoid arthritis (RA), it's also positive in many other connective tissue disorders that may be confused with RA. For instances, the RF test may be positive in Sjogren's syndrome and in lupus disorders.
The test for cyclic citrullinated peptide (CCP) antibodies, however, is specific for rheumatoid arthritis. A positive test result for CCP confirms RA, and it's also advantageous because the CCP shows up as positive earlier in the disease course. The RF test may also be negative in the absence of an active disease flare in RA.
When tests for RF and CCP are both negative and symtoms of systemic arthritis exist, tests for the arthritic conditions called spondyloarthropathies should be evaluated.