Serum β2-microglobulin level is a useful indicator of disease activity and hemophagocytic syndrome complication in systemic lupus erythematosus and adult-onset Still's disease.

This study demonstrates whether serum β2-microglobulin (β2-MG) level can be an indicator of the status of systemic lupus erythematosus (SLE) and adult-onset Still's disease (AOSD), and development of hemophagocytic syndrome (HPS) complication. Serum β2-MG level was compared between the active and inactive statuses of SLE and AOSD in hospitalized patients. Active status was defined as a state for which a therapy was introduced. Serum β2-MG level was also compared between patients with and without HPS complication. HPS was diagnosed on the basis of clinical and pathological findings. Laboratory markers of HPS including peripheral blood cell counts and levels of serum lactate dehydrogenase (LDH), serum ferritin, plasma fibrin/fibrinogen degradation product (FDP), and plasma D-dimer were examined to determine their correlations with serum β2-MG level. Sixteen SLE and seven AOSD patients (all females, aged 39.0 ± 16.4) were included. The serum β2-MG level was high in the active status of underlying diseases and decreased significantly after the therapy (3.5 ± 1.4 vs. 2.1 ± 0.8 mg/L, p < 0.001). Among patients with active status, the β2-MG level was higher in patients with HPS (two with SLE and three with AOSD) than in patients without HPS (4.9 ± 1.8 vs. 3.3 ± 1.4 mg/L, p < 0.05). Serum β2-MG level significantly correlated with the levels of serum LDH (r(s) = 0.42, p < 0.05), plasma FDP (r(s) = 0.58, p < 0.05), and plasma D-dimer (r(s) = 0.77, p < 0.01). Serum β2-MG level would be a useful indicator of disease activity and development of HPS complication in patients with SLE and AOSD.