The presence of F cells with a fetal phenotype in adults with hemoglobinopathies limits the utility of flow cytometry for quantitation of fetomaternal hemorrhage.

Background: Detection and quantitation of fetomaternal hemorrhage (FMH) can be difficult in patients with pre-existing elevations of HbF, such as those with hemoglobinopathies. The aim of this study was to evaluate the utility of dual-color flow cytometry with the Fetal Cell Count Kit (FCCK) in differentiating adult and fetal HbF in this population, as compared to flow cytometry (FC) using HbF alone.

Methods: Peripheral blood was obtained from normal adults and patients with hemoglobinopathies (β-thalassemia and sickle cell disease), including a small number of pregnant females. Cord blood was used to spike some samples with 5% fetal cells. Analysis by single color (HbF) and dual-color (HbF and carbonic anhydrase) FC was performed on these samples. Fetal cells were defined as those with high HbF fluorescence on single-color FC, and those that were HbF + CA- using the FCCK. The quantity of fetal cells detected by each technique was compared.

Results: Forty-six adult patients were included. In non-pregnant adults with hemoglobinopathies, a population of red cells with a fetal cell phenotype were detected by both techniques. The dual-color method reported lower quantities of these cells. In nineteen samples spiked with cord blood the FCCK consistently underestimated the quantity of fetal cells.

Conclusions: Patients with β-thalassemia and sickle cell disease have a population of HbF-containing cells which are phenotypically similar to fetal cells. Even with dual-color flow cytometry (FCCK), the detection and quantification of FMH by flow cytometry in this population remains difficult. © 2017 International Clinical Cytometry Society.