Evaluation of disease activity by laboratory tests in juvenile rheumatoid arthritis.

We studied 29 juvenile rheumatoid arthritis patients with polyarticular onset in order to detect the presence of disease activity by laboratory tests. Laboratory studies included hemoglobin, hematocrit, erythrocyte sedimentation rate (ESR), white blood cell (WBC) and platelet counts. We also determined the levels of IgG, IgA, IgM, C3, C4 and C reactive protein, as well as the presence of rheumatoid factor and antinuclear antibodies. There were 13 patients in the group with polyarticular disease activity, and 16 in the group with asymptomatic juvenile rheumatoid arthritis. Low hematocrit and hemoglobin values, abnormal ESR and elevated WBC and platelet counts occurred in polyarticular juvenile rheumatoid arthritis patients with active disease. Increased levels of IgA, C3 and C4 were also found in the exacerbation stage, as compared to the asymptomatic control group. No differences were found in rheumatoid factor and antinuclear antibodies between the active and inactive juvenile arthritis patients. Our data agreed with previous studies in that a single laboratory test cannot necessarily confirm juvenile arthritis activity, and they suggest that two or more abnormal parameters would be useful in assessing the flare-up of the disease.