sCD177/PR3 is detectable in the supernatant from RBC concentrates. (A) The concentration of sCD177/PR3 was measured in fresh RBCs (day 1) and stored RBCs (day 21) before and after filtration using standard blood bank procedures (left). As control, the albumin concentration in RBCs before and after filtration was assessed (right). (B) Evaluation of sCD177/PR3 protein content in sera from TRALI patients and 3 donors. The serum sample from the TRALI patient and 3 donors were analyzed in ELISA. Note, donor 1 was involved in TRALI reaction. The values are representative of 3 independent tests and are presented as mean ± SD. **P < .01.