Laboratory Testing for Osteoarthritis
Laboratory tests are not indicated for the diagnosis of osteoarthritis, as the diagnosis is made clinically based on age, joint pain pattern, and minimal morning stiffness, with radiography used only for confirmation when needed.
Clinical Diagnosis Without Laboratory Testing
Osteoarthritis should be suspected and diagnosed clinically without routine laboratory work 1, 2:
- Patients older than 50 years with joint pain, minimal morning stiffness (typically less than 30 minutes), and functional impairment likely have OA 1
- The diagnosis is based on history of joint pain worsened by movement and weight-bearing activity 2, 3
- Commonly affected joints include fingers, shoulders, hips, knees, and ankles, especially in patients over 40 years 1
When Laboratory Testing May Be Appropriate
Blood tests should be performed only to exclude other conditions that can mimic or cause secondary osteoarthritis 4:
- Inflammatory arthritis (rheumatoid arthritis, psoriatic arthritis): ESR, CRP, rheumatoid factor, anti-CCP antibodies
- Crystal arthropathy (gout, pseudogout): Serum uric acid, joint aspiration for crystal analysis
- Metabolic bone disease: Calcium, phosphate, alkaline phosphatase, vitamin D
- Septic arthritis: Joint aspiration with cell count, Gram stain, and culture when infection is suspected 5
Laboratory testing is not useful for diagnosing or monitoring osteoarthritis itself 2, 4.
Imaging as the Confirmatory Tool
Plain radiographs are the appropriate confirmatory test when imaging is needed 5:
- X-rays of the affected joint area are rated 9/9 (usually appropriate) for suspected osteoarthritis 5
- Radiographic findings include joint space narrowing, osteophytes, subchondral sclerosis, and bone cysts 2, 3
- Important caveat: Radiographic findings often do not correlate well with symptom severity 1
- Imaging is most helpful before surgical referral or when the diagnosis is uncertain 1
Common Diagnostic Pitfalls to Avoid
- Ordering routine inflammatory markers (ESR, CRP) in typical OA cases—these are normal in primary OA and only useful to exclude inflammatory arthritis 2, 4
- Obtaining radiographs in every patient—clinical diagnosis is sufficient in typical presentations 1
- Misinterpreting radiographic severity—severe radiographic changes may exist with minimal symptoms and vice versa 1
- Missing secondary causes—always consider trauma history, metabolic disorders, or inflammatory conditions in atypical presentations 3, 6