Donor AAT levels and acute GVHD (n = 111) by day 100. Plasma AAT levels in human allogeneic transplant donors. Donor AAT levels and the development of GVHD (by grade) in the respective recipients by day 100. GVHD severity increased with decreasing AAT levels. Modeling GVHD severity as a linear variable, a trend test showed decreasing average AAT plasma levels with increasing GVHD scores (P = .0006). This same conclusion held for GVHD scores by day 20 (P = .01) and by day 30 (P = .002) (not shown).