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Arthritis & rheumatoid arthritis

Arthritis testing: from diagnosis to prognosis and monitoring

We understand arthritis is one of the main reasons patients may find themselves in your office. In fact, arthritis affects more than 20% of American adults—over 50 million people. It is also one of the most common health complaints in the United States, and the leading cause of disability.1,2

That’s why Quest Diagnostics is committed to helping you quickly identify the source of your patients’ symptoms, allowing you to speed treatment and minimize the impact of disease. From first-line tests to monitoring, turn to Quest for the right test for the right patient at the right time.

14-3-3η (eta) protein: insight from innovation

More than 100 different diseases fall under the umbrella term “arthritis.”3 Their symptoms can be similar, making diagnosis challenging—and speed to diagnosis critical—to ensure timely management of symptoms and disease progression. Our growing portfolio of tests can help you distinguish between different forms of arthritis, speeding diagnosis and time to treatment.

At Quest, we’re driven by innovation. Our testing evaluates some of the newest tools for diagnosis—like the 14-3-3η (eta) protein, a predictor of early inflammation for rheumatoid arthritis (RA) and erosive psoriatic arthritis (PsA). This protein is released into synovial fluid and blood when there is inflammation associated with joint erosion and may play a biologic role in the erosive process. Blood levels appear elevated in patients with RA and PsA, but not in other diseases.4

A test for the 14-3-3η protein is available from Quest Diagnostics as an individual biomarker, as well as within our comprehensive panels. If RA and PsA are diagnosed early (ie, before significant joint erosion occurs), treatment can help to prevent irreversible damage. 

Comprehensive arthritis and rheumatoid arthritis testing portfolio

Treat rheumatoid arthritis early to help slow joint erosion

Rheumatoid arthritis (RA)—the inflammatory “flaring” arthritis—is a systemic autoimmune disease. Approximately 165,000 new cases are diagnosed annually in the United States.5 All parts of the body can be affected, including the heart and lungs, but RA is often characterized by symmetrical finger and wrist pain. One of the most potentially devastating forms of arthritis, it typically appears in the third and fourth decades of life and affects women more frequently than men.

Quest offers a full suite of testing for RA, including a test for the 14-3-3η protein biomarker.

Rheumatoid arthritis tests:

*Panel components may be ordered separately.

Get the differential diagnosis you need for osteoarthritis

Known as the “wear and tear” arthritis, osteoarthritis (OA) is the most common form of arthritis, affecting over 30 million Americans.6

Many symptoms of OA and RA overlap, including pain, swelling, and stiffness in the joints. These similarities can cause difficulty when differentiating the diseases. Differential diagnosis of OA and RA is important because treatments differ.7

Depending on the joint, classification criteria may include joint symptoms (pain, stiffness, swelling, enlargement, deformation), age, erythrocyte sedimentation rate, radiologic findings (presence of osteophytes or narrowing of joint space), synovial fluid tests (color, appearance, white blood cell count), and the sensation of crackling in the joint (crepitus).8

In addition, some laboratory markers are elevated in RA patients but normal in OA patients. A positive or elevated result for rheumatoid factor, cyclic citrullinated peptide antibody, or the 14-3-3η protein may suggest inflammatory arthritis, such as RA, rather than OA.

Osteoarthritis tests:

Identify psoriatic arthritis with emerging biomarker testing

Psoriatic arthritis (PsA) occurs in about 10% to 20% of people with psoriasis.9 While PsA is similar to RA, it is more serious, because it extends to the joints, ligaments, and tendons.

Evaluation of a patient for psoriatic arthritis may include a personal and family history and a physical exam. Helpful laboratory tests include10:

  • Rheumatoid factor and cyclic citrullinated peptide antibody to rule out RA
  • C-reactive protein and/or erythrocyte sedimentation rate to document inflammation
  • Hemoglobin or CBC to test for anemia

A marker of erosive arthritis in psoriasis: the 14-3-3η protein

Patients with psoriasis have normal 14-3-3η levels, as do psoriasis patients with nonerosive arthritis. However, patients with erosive psoriatic arthritis may have elevated 14-3-3η. As a result, elevations in 14-3-3η in followed psoriasis patients may herald onset of erosive disease.11 Quest incorporates a longitudinal view of the patient’s 14-3-3η test results for ease of monitoring.

Psoriatic arthritis tests:

The power of Quest



  1. Barbour K, Helmick CG, Boring M, et al. Vital signs: prevalence of doctor-diagnosed arthritis and arthritis-attributable activity limitation - United States, 2013-2015. MMWR Morb Mortal Wkly Rep. 2017;66(9):246-253. doi:10.15585/mmwr.mm6609e1
  2. Courtney-Long E, Carroll DD, Zhang QC, et al. Prevalence of disability and disability type among adults—United States, 2013. MMWR Mort Wkly Rep. 2015;64(29):777-783. doi:10.15585/mmwr.mm6429a2
  3. CDC. Arthritis types. Updated February 20, 2019. Accessed September 3, 2021.
  4. Maksymowych WP, Boire G, van Schaardenburg D, et al. 14-3-3η autoantibodies: diagnostic use in early rheumatoid arthritis. J Rheumatol. 2015;42:1587-1594.
  5. Alamanos Y, Voulgari PV, Drosos AA. Incidence and prevalence of rheumatoid arthritis, based on the 1987 American College of Rheumatology criteria: a systematic review. Semin Arthritis Rheum. 2006;36(3):182-188. doi:10.1016/j.semarthrit.2006.08.006
  6. CDC. Osteoarthritis. Reviewed July 27, 2020. Accessed September 3, 2021.
  7. Hochberg MC, Altman RD, April KT, et al. American College of Rheumatology 2012 recommendations for the use of nonpharmacologic and pharmacologic therapies in osteoarthritis of the hand, hip, and knee. Arthritis Care Res (Hoboken). 2012;64(4):465-474. doi:10.1002/acr.21596
  8. Hunter DJ, Nevitt M, Losina E, et al. Biomarkers for osteoarthritis: current position and steps towards further validation. Best Pract Res Clin Rheumatol. 2014;28(1):61-71. doi:10.1016/j.berh.2014.01.007
  9. Mease P. Update on treatment of psoriatic arthritis. Bull NYU Hosp Jt Dis. 2012;70(3):167-171. 
  10. American College of Rheumatology. Psoriatic arthritis. Updated March 2019. Accessed March 19, 2014
  11. Maksymowych WP, Naides SJ, Bykerk V, et al. Serum 14-3-3η is a novel marker that complements current serological measurements to enhance detection of patients with rheumatoid arthritis. J Rheumatol. 2014; 41(11):2104-2113. doi:10.3899/jrheum.131446