The monocyte monolayer assay: a noninvasive technique for predicting the severity of in utero hemolysis

To test the noninvasive monocyte monolayer assay in predicting hemolytic severity in utero, we studied 18 patients from two institutions with significant erythrocyte alloantibodies. Serum samples were obtained from each patient. Each subject donated a serum sample during her pregnancy. Monocytes were harvested from a single healthy donor and grown in monolayer culture. Erythrocytes with the appropriate antigens were sensitized with maternal serum and incubated with the monocyte monolayers. Erythrophagocytosis was scored as a percentage of the positive control. Perinatal outcomes were assessed post hoc and cases were classified as unaffected or mildly, moderately, or severely affected using standard definitions. Prenatal management was conducted without knowledge of the results. Six of the 18 patients had severe disease and one of the 18 had moderately severe disease. At a cutoff level of 20, the assay generated the following results: sensitivity was 7 of 7 (100%), specificity was 10 of 11 (90.9%), positive predictive value was 7 of 8 (87.5%), and negative predictive value was 10 of 10 (100%). The monocyte monolayer assay appears to be a useful, noninvasive modality for predicting the severity of hemolytic disease in utero.