Microheterogeneity of alpha1‐acid glycoprotein in the detection of intercurrent infection in systemic lupus erythematosus

Abstract

We evaluated the clinical usefulness of determinations of α₁-acid glycoprotein microheterogeneity patterns in distinguishing patients who have active systemic lupus erythematosus (SLE) from those who have SLE with intercurrent infection. We used agarose affinity electrophoresis with concanavalin A (Con A) as a ligand. Results were expressed as reactivity coefficients (RC), which are the ratios of variants reactive with Con A to the variants not reactive with Con A. No significant differences were found between the mean RC (±SD) in healthy individuals (1.35 ± 0.26) and that in patients with various degrees of SLE activity. In contrast, a significantly higher mean RC was found in sera from patients with intercurrent infection (2.70 ± 0.76) compared with each of the other groups studied (P < 0.001). An RC > 2.25 was found in none of 42 sera from patients without infection and in 15 of 18 sera from patients with infection (sensitivity 83%, specificity 100%). C-reactive protein (CRP) levels were also significantly higher in SLE patients with intercurrent infection than in patients with very active disease (P < 0.05). Levels of CRP >60 mg/liter were found in 3 of 42 SLE patients without infection and in 8 of 18 patients with infection (sensitivity 39%, specificity 93%). The results show that in SLE patients, the finding of a relative increase in Con A—bound serum α₁-acid glycoprotein is a more sensitive indicator of intercurrent infection than is the finding of increased levels of CRP.