Objective: The authors report here our experience using the gel test to follow up chimerism in a 5 year old girl with β thalassemia/Hemoglobin E disease (β thal/HbE), post allogeneic bone marrow transplantation with Hb E trait HLA identical sibling donor. They were ABO blood group major mismatched donorrecipient pairs (donor and recipient blood group are B and O, respectively).
Material and Method: Pre and post transplanted EDTA blood samples from the girl with β thalassemia/Hemoglobin E were tested for ABO, Rh and direct antiglobulin test (DAT) using the A-B-AB-D-ctl/AHG card and the titer of anti-A and anti-B were tested by the conventional tube technique. The sex chromosome study and hemoglobin typing were also examined.
Results: In this technique, mixed field agglutination is clearly identified from positive and negative results. The authors detected peripheral recovery, mixed O/B population after transplantation on day +26 with positive DAT. The DAT was negative on day +67 after transplantation and the recipient blood group was completely changed to B on day +123. In addition, Hb typing was changed to Hb E trait with Hb F less than 5 % on day +37. The engraftment of neutrophils, more than 5x109/L, was detected on day+14 and platelet count was more than 20x109/L on day +28. On day +90, the patient was transfusionindependent with the mean Hb level at 11.4 g/dL (10.4-13.1). The sex chromosome and hemoglobin typing were changed to the donor on day +300.
Conclusion: The gel test is an alternative method which is simple and helpful in detecting mixed red blood cell populations, particularly in the ABO or other blood group mismatched bone marrow transplantation.

Keywords: Gel test, Chimerism