There is no specific laboratory test to diagnose OA. It is diagnosed using someone's personal and family medical histories, a physical exam, X-rays, and in some cases with an examination of synovial fluid from an affected joint. Tests that may be ordered to rule out other conditions and to evaluate the person's health include:
- Rheumatoid factor (RF) and Cyclic citrullinated peptide antibody (CCP) – to help diagnose rheumatoid arthritis (RA) and differentiate it from osteoarthritis; both tests are positive with RA and generally negative in OA.
- Synovial fluid analysis – to look for signs of joint infection and to detect monosodium urate (uric acid) crystals that could indicate gout or calcium pyrophosphate crystals that may contribute to joint damage in osteoarthritis
- Erythrocyte sedimentation rate (sed rate or ESR) – to detect inflammation in the body; ESR will be increased in RA but not in osteoarthritis.
- C-reactive protein (CRP) – to detect inflammation and test for the activity of the disease; may be used to help differentiate osteoarthritis and RA; an increased level of CRP occurs in RA but not in osteoarthritis.
- Complete blood count (CBC) – to help evaluate red and white blood cells and hemoglobin; may be ordered to monitor the side effects of some OA treatments
- Comprehensive metabolic panel (CMP) – to help evaluate and monitor kidney and liver function
- X-rays of the affected joints may show loss of cartilage, bone damage, bone spurs, and narrowing of the joint space but will frequently not show significant changes early in the disease.
- MRI (magnetic resonance imaging) – may also be used to examine affected joints