Laboratory markers available for the diagnosis of RA, including rheumatoid factor (RF), cyclic citrullinated peptide (CCP) antibody, and the 14.3.3 eta protein.
RF is an autoantibody that targets the Fc region of IgG. It is widely used as a laboratory marker of RA because serum levels are often elevated in RA patients.
The sensitivity of RF testing is 60% to 86% for established RA and 57% for early RA.
The usefulness of RF testing is somewhat limited by its low specificity: 70% to 85% for established and early RA.
Cyclic citrullinated peptide (CCP) identifies autoantibodies to citrullinated
peptides, which are often elevated in RA patients.
CCP testing has similar sensitivity for established RA (64% to 88%)2,7 and early RA (59%)4; however, specificity (90% to 99%) is higher for both established and early RA.
CCP antibody testing is at least as sensitive as and more specific than RF testing in various clinical situations.
CCP testing is more specific than RF testing, but is is not considered a replacement for RF testing.
Serology tests for both markers provides greater sensitivity than the use of either alone.
Between 28% and 44% of patients with early RA test negative for both RF and CCP antibody, and patients who develop erosive RA may remain negative for both markers.
The 14-3-3η protein biomarker for the detection of RA, may play a role in stimulating tumor necrosis factor alpha, metalloproteinases, and other inflammatory mediators critical to the joint erosive process.
14-3-3η protein is found in the central nervous system and synovial joint tissue.
The 14-3-3η protein is released into the extracellular space such as synovial fluid and peripheral blood,when synovial inflammation associated with joint erosion is present in RA and psoriatic arthritis.
14-3-3η tends to be elevated in patients with RA, but not in other diseases including osteoarthritis, osteoporosis, gout, psoriasis, CROHN’S disease, ulcerative colitis, type 1 diabetes, systemic lupus erythematosus, primary sjogren’s syndrome, scleroderma, or multiple sclerosis.
14-3-3η as an RA marker is that it can improve identification rates of early RA.
The benefit of increased sensitivity allows earlier detection and treatment in the course of disease, which can minimize irreversible joint damage.
The median concentration is 6.13 ng/mL in early RA patients with joint damage and 1.30 ng/mL in those without joint damage.
The 14-3-3η protein is also a biomarker for the detection of erosive psoriatic arthritis.
Both RA and psoriatic arthritis can be difficult to diagnose clinically early in the disease process and can be associated with early joint erosion.
Psoriatic arthritis affects approximately 30% of patients with psoriasis.
With psoriatic arthritis, 14-3-3η positivity may help differentiate those with joint damage from those without joint damage.
The median 14-3-3η levels are higher in patients with erosive psoriatic arthritis (0.23 ng/mL) than nonerosive psoriatic arthritis (0.0 ng/mL).
14-3-3η results may help differentiate RA from osteoarthritis.
Testing useful: in Individuals suspected of having RA
In Individuals with psoriatic arthritis
In Individuals with arthritis requiring differential diagnosis of osteoarthritis from RA or erosive psoriatic arthritis
14-3-3η protein: <0.2 ng/mL