What is the role of blood tests and urinalysis in the workup of reactive arthritis (ReA)?

Updated: Dec 24, 2020
  • Author: Carlos J Lozada, MD; Chief Editor: Herbert S Diamond, MD  more...
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The values of acute-phase reactants, including erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), are usually elevated markedly (eg, ESR of 50-60 mm/hr) but later return to the reference range when the inflammation subsides. C1, C4, and C5 levels are within the reference range. C1 inhibitor functional assay (C1INH) and C2 levels may be elevated.

Other laboratory findings include a normocytic normochromic anemia along with mild leukocytosis (up to 20,000/µL) and thrombocytosis during the acute phase. Immunoglobulin A (IgA) antibodies to specific bacterial antigens have been reported. Test results for rheumatoid factor and antinuclear antibodies are negative.

Referral for HIV should be considered in patients presenting with history, symptoms, or findings suggesting increased risk for the disease; certain therapies are contraindicated in these patients. [63] The incidence of ReA is high among patients with AIDS, and HIV testing is mandatory in patients in whom ReA is newly diagnosed, even if they do not have the risk factors.

White blood cells (WBCs), red blood cells (RBCs), and small amounts of protein are present in urinalysis findings, indicating pyuria. Urine culture findings may be positive for Chlamydia or Ureaplasma, though test results may be negative if obtained several weeks after the onset of symptoms.

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