Microheterogeneity of alpha 1-acid glycoprotein in the detection of intercurrent infection in patients with rheumatoid arthritis.

We evaluated the clinical usefulness of determinations of alpha 1-acid glycoprotein (AGP) microheterogeneity in distinguishing patients who have active rheumatoid arthritis (RA) from those who have RA and an intercurrent infection. AGP microheterogeneity was studied by affinity electrophoresis with concanavalin A as the ligand, and the results were expressed as reactivity coefficients (RC). Significant differences were found between the mean RC (+/- SD) in healthy individuals (1.27 +/- 0.16) and the mean RC in RA patients with intercurrent infection (1.74 +/- 0.90), as well as with the mean RC in RA patients with grades III and IV disease activity (0.92 +/- 0.18 and 0.81 +/- 0.25, respectively). Moreover, an additional microheterogeneous form of AGP, similar to that observed in non-RA patients with infections, was noted in RA patients with infections (sensitivity 100%, specificity 100%). The results show that an increase in AGP reactivity with concanavalin A is a sensitive indicator of intercurrent infection in patients with RA.