This is not an uncommon situation. For quite a few years, I was in charge of a prenatal testing lab at Memorial Blood Centers. One of the services we provided was Kleihauer-Betke testing. For quite a few years we repeated FMH screens on samples submitted for Kleihauer-Betke testing due to pos FMH screens when the Kleihauer-Betke test was negative. We followed the FMH screen procedure published by Betty Sebring, who, also, worked at Memorial. In all cases, the FMH screen test in our hands was negative.