[Transfusion requirements and mean annual hemoglobin level in thalassemia major]. / Apports transfusionnels et taux d'hémoglobine moyen annuel dans la thalassémie majeure.

The blood requirements using packed red cells (C) and the mean annual haemoglobin level (Hb ma), corresponding to the mean of all haemoglobin levels before (Hb pre T) and after (Hb post T) transfusion over 1 year, have been measured in 14 splenectomized and regularly transfused thalassaemia major patients. In these non-hypersplenic patients a linear relation was determined between C and Hb ma. The blood consumption C has also been measured in 5 patients with hypersplenism. The comparison of C between these two groups of patients offered the possibility of defining the limit of C, for a given value of Hb ma, above which hypersplenism is indicated. The measurement of Hb ma requires the value of Hb post T, a parameter which is sometimes difficult to obtain in practice. For this reason, a method of calculating Hb post T using Hb pre T, C and the number of transfusions over 1 year (N) is described. The relation between these parameters is: Hb post T = Hb pre T + C/N X 0.23. To use this formula, the conditions must be as follows: the haematocrit of blood units must be between 75% and 85%, and the blood volume of each transfusion in a given patient must be identical throughout the year.