A retrospective analysis of the value of monocyte monolayer assay results for predicting the clinical significance of blood group alloantibodies

BACKGROUND: Cellular assays (e.g., monocyte monolayer assays [MMAs]) have been used to predict the clinical significance of red blood cell (RBC) alloantibodies. STUDY DESIGN AND METHODS: Twenty years of MMA data were retrospectively analyzed to 1) determine the optimal cut point (by correlating MMA results from 46 patients with RBC survival study results and/or laboratory and clinical signs of hemolytic transfusion reactions [HTRs] when incompatible blood was transfused), and 2) determine what percentage of 251 unusual alloantibodies (most to high-incidence antigens) were predicted to be clinically significant. RESULTS: Two MMA cut points (5% and 20%) were chosen using a receiver-operating characteristics curve. No patients with MMA results less than or equal to 5 percent had clinical signs of a reaction; one-third of patients with MMA results 5.1 to 20 percent versus two-thirds with results greater than 20 percent had clinical signs of a HTR after transfusion of incompatible blood. Using 5-percent or 20-percent cut points, 173 (69%) or 97 (39%) of 251 unusual alloantibodies gave positive MMAs, respectively. CONCLUSION: A negative MMA (less than or equal to 5%) indicates that incompatible blood can be given without risk of an overt HTR but does not guarantee normal long-term survival of those RBCs. Most unusual alloantibodies are predicted to cause shortened RBC survival, but transfusion of incompatible blood may not result in any clinical or laboratory signs of a HTR. We have used the MMA for approximately 20 years, instead of a 1-hour chromium-51 RBC survival, to aid in the decision to transfuse RBCs incompatible with antibodies to high-incidence antigens.