How is Reactive Arthritis diagnosed
Which laboratory investigations are useful in confirming the diagnosis of ReA?
The diagnosis of ReA is clinical, and no laboratory investigation can substitute for a proper history and physical examination. However, they can be used in confirming the clinical diagnosis. Arthrocentesis is the most valuable test because it excludes septic and crystalline arthritis.
Laboratory Investigations that Are Useful in Confirming the Diagnosis of Reactive Arthritis
| Expected Result | |
|---|---|
| Primary (essential) | |
| ESR and/or CRP | Elevation |
| Complete blood count and differential | Polymorphonuclear leukocytosis |
| Thrombocytosis and anemia of chronic disease | |
| Rheumatoid factor | Negative |
| Urinalysis | Pyuria, microhematuria +/– bacteria |
| Synovial fluid analysis | Moderate leukocytosis |
| Negative Gram stain and no crystals | |
| Cultures and/or PCR | |
| —Throat | (+/–) ( Chlamydia ) |
| —Urine | (+/–) ( Chlamydia ) |
| —Stool | (+/–) ( Yersinia and Salmonella can persist for weeks) |
| —Synovial fluid | Negative cultures |
| —Urethra/cervix | (+/–) ( Chlamydia ) |
| —Sputum | (+/–) ( Chlamydia pneumonia ) |
| Secondary (optional) | |
| Antinuclear antibody | Negative |
| Antibody serology | Positive (e.g., Yersinia , Shigella , and Chlamydia ) |
| Blood cultures | Negative, unless septic |
| Radiographs | |
| • Peripheral joints | Arthritis, enthesitis |
| • Axial joints | Spondylitis, enthesitis |
| • Anteroposterior pelvis | Sacroiliitis |
| Electrocardiogram | Heart block |
| Colonoscopy | Ileitis/colitis |
Note: In 40% of reactive arthritis patients an infectious agent cannot be identified. Urine polymerase chain reaction for Chlamydia and stool cultures may be helpful in patients with urethritis or diarrhea, respectively. Serologic tests for Chlamydia, Salmonella, and Yersinia can be done depending on the suspected inciting agent.CRP , C-Reactive protein; ESR , erythrocyte sedimentation rate; PCR , polymerase chain reaction.
