Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (16 page)

   Number and site/size of involved joints (score range 0–5)

   Serologic abnormality, based on serum levels of RF and anti–citrullinated protein antibody (score range 0–3)

   Elevated acute-phase response, based on CRP and ESR (score range 0–1)

   Symptom duration (< or ≥6 weeks; range 0–1)

   Who Should Be Suspected?

   Candidates are individuals presenting with fatigue, weakness, anorexia, and slowly progressive pain and swelling of the joints. Involvement of the small joints of the hands or feet should raise suspicion of RA. Early symptoms may also include fatigue, muscle pain, low-grade fever, weight loss, and numbness and tingling of the hands.

   Onset of RA most often occurs between the fourth and sixth decades of life but can also be seen in the pediatric population (juvenile rheumatoid arthritis) as well as the elderly. Women are three times more likely to develop RA than are men.

   Sixty to seventy percent of RA patients of European ancestry carry the
HLA-DR4
gene compared to 30% in the general population, indicating a genetic predisposition.

   Laboratory Findings

There is no pathognomonic test for RA. Tests for diseases that can mimic RA (hemochromatosis, SLE, systemic sclerosis, sarcoidosis) may be indicated.

   RF is positive in approximately 80% of patients within one year of presentation, but in only 30% at the onset of arthritis. In the absence of RF (15–20% of cases), the disease is called seronegative RA.

   Anti–citrullinated protein antibody, tested as anti-CCP or anti–mutated citrullinated vimentin, is more specific for RA than RF. Anti-CCP antibodies are found in 60–70% of RA cases and have approximately 95% specificity.

   ANA test is positive in 25–50% of patients.

   Synovial fluid analysis reveals an inflammatory pattern with increased WBC counts (2,000–50,000/μL in affected joints), with a predominance of neutrophils. Total hemolytic complement, C3, and C4 are markedly reduced.