The Monocyte Monolayer Assay: Past, Present and Future

Serologic testing using the indirect antiglobulin test (IAT) is known to be insufficient to determine the clinical significance or insignificance of a given antibody to red blood cells (RBC), particularly in cases of antibodies to high-prevalence antigens, such as anti-Ge or anti-Yt^a. An in vitro functional cellular assay, the monocyte monolayer assay (MMA), has been studied for more than 40 years for its potential use to differentiate between clinically significant and insignificant RBC antibodies. The MMA has recently been used to select donor blood for transfusion into patients having a serologically incompatible crossmatch, without any obvious sequalae. Thus, the MMA shows great potential for future use to select donor blood for transfusion in situations where antibodies to high-prevalence antigens or complex multiple alloantibody problems confront transfusion services. In this report, we review the history leading up to the current uses of the MMA, its optimization, and potential use for the selection of serologically incompatible donor blood for transfusion. We describe current ongoing work to document and improve the efficacy of the MMA. Finally, we briefly describe possible future directions to make the MMA more amenable to routine laboratories.