To determine the diagnostic and screening test qualities of concentrations of the CD8+ lymphocyte subset in peripheral blood to discriminate patients with giant cell arteritis (GCA) from patients with other diseases.
A CD8+ lymphocyte test was performed in 454 patients from the Department of Medicine, Randers Central Hospital. The sensitivity, specificity and predictive values of the test were calculated and presented as receiver operating characteristic (ROC) curves.
The median percentage and numbers of CD8+ cells were significantly reduced in 227 patients with active untreated GCA compared with 227 in-patients of similar age and sex (GCA vs in-patients CD8% : 12.0 vs 20.0, CD8+ x 10(9)/l : 0.195 vs 0.374, p < 0.05). Identical ROC curves were obtained when patients with GCA were tested against various subgroups of patients. The sensitivity and specificity of the test for GCA at an optimal cutoff point were 71% and 80%, respectively, while the positive predictive value was 80%.
At an optimal cutoff point, concentrations of the CD8+ lymphocyte subset in peripheral blood discriminate patients with GCA from patients with other diseases. The sensitivity and specificity of the test for GCA are equal to those of other tests used in rheumatology.