Cytometry and Rhesus: not only for haemolytic disease of the newborn

Since the 1960s, when passive immunoprophylaxis with intramuscular administration of adequate doses of anti-D immunoglobulin was introduced to prevent maternal-foetal Rhesus (Rh) immunisation, the number of cases of haemolytic disease of the newborn (HDN) has decreased dramatically1–2. The most widely used test to detect the presence of foetal erythrocytes in maternal blood is the acid elution method described by Kleihauer-Braun-Betke3. Since the 1990s, other methods have been adopted for routine laboratory assessment of the degree of foetal-maternal haemorrhage (FMH), such as flow cytometric search for Rh-positive erythrocytes with monoclonal antibodies4 and the agglutination test on a card (gel agglutination technique, GAT). In our laboratory, we use the flow cytometric method, which selectively quantifies the circulating Rh-positive erythrocytes, by using a monoclonal antibody directed to the erythrocyte D antigens (Quanti-D Pe, Millipore). This method has the obvious advantages of sensitivity, specificity, objectivity and is faster than the traditional one5–6. The extreme specificity of the test has led us to adopt it not only to quantify the extent of FMH in order to prevent HDN, but also for other purpose. Here we illustrate two cases in which the use of flow cytometry helped us to explain clinical problems and to detect transfusion errors.