How is Reactive Arthritis diagnosed

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 CRPElevation
Complete blood count and differentialPolymorphonuclear leukocytosis
Thrombocytosis and anemia of chronic disease
Rheumatoid factorNegative
UrinalysisPyuria, microhematuria +/– bacteria
Synovial fluid analysisModerate leukocytosis
Negative Gram stain and no crystals
Cultures and/or PCR
—Throat(+/–) ( Chlamydia )
—Urine(+/–) ( Chlamydia )
—Stool(+/–) ( Yersinia and Salmonella can persist for weeks)
—Synovial fluidNegative cultures
—Urethra/cervix(+/–) ( Chlamydia )
—Sputum(+/–) ( Chlamydia pneumonia )
Secondary (optional)
Antinuclear antibodyNegative
Antibody serologyPositive (e.g., Yersinia Shigella , and Chlamydia )
Blood culturesNegative, unless septic
• Peripheral jointsArthritis, enthesitis
• Axial jointsSpondylitis, enthesitis
• Anteroposterior pelvisSacroiliitis
ElectrocardiogramHeart block

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.


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