Red blood cell alloimmunisation and autoimmunisation in transfusion dependent beta thalassemics from Southern India

Introduction

Treatment modalities for patients with beta thalassemia major include chronic transfusion therapy, iron chelation, splenectomy, and allogeneic hematopoietic transplantation. The goal of long-term transfusion support is to maintain the patient's hemoglobin at 9.5-10 g/dL, thus improving his or her well-being while simultaneously suppressing enhanced erythropoiesis. Although chronic blood transfusion is lifesaving, this is associated with complications like erythrocyte alloimmunization and autoimmunization and poses a major challenge for repeated transfusions in these patients. Allogeneic blood transfusion is a form of temporary transplantation and this procedure introduces a multitude of foreign antigens and living cells into the recipient that persist for a variable period of time. A recipient who is immunocompetent often mounts an immune response to the donor antigens, resulting in various clinical consequences, depending on the blood cells and specific antigens involved. The factors responsible for alloimmunization are complex and involve antigenic differences on the red cell between the blood donor and the recipient ; the recipient's immune status ; and the immunomodulatory effect of the allogenic blood transfusions on the recipient's immune system(1). Some alloantibodies are hemolytic and may cause, though not invariably, hemolytic transfusion reactions and limit the availability for further safe transfusions. Others are clinically insignificant. The frequency of alloimmunisation among thalassemics in India ranges from 3.79% to 18.8% (2, 3, 4) and across the world frequency ranges from 2.7% to 37% (5)

Erythrocyte autoantibodies appear less frequently but they can result in clinical hemolysis and difficulty in cross matching of blood. Patients with autoantibodies may have a higher transfusion rate and often require immunosuppressive drugs, splenectomy or alternative options in treatment. (6, 7, 8).

Material and Methods

This was a cross-sectional descriptive study conducted in Kasturba Medical College Hospital, Attavar, Mangalore from January 2011 to December 2011, after obtaining informed consent from the parents of all patients. Time bound Research Ethics Committee had approved the study. Study was conducted in 55 beta-thalassemia patients who were on regular blood transfusion.

Parents were interviewed and the transfusion records were examined for the details like, age of the patient, age at diagnosis and initiation of transfusion therapy, total number of blood units transfused (transfusion of whole blood or packed cells in ml/kg was calculated from the records and then number of units), type of blood transfused (whole blood or packed cells; leucoreduced or non-leucoreduced blood), transfusion interval, status of splenectomy and detailed clinical evaluation. Investigations done were - peripheral smear, to look for evidence of any significant hemolysis , a screening test to detect the presence of antibodies directed against red blood cell antigens belong to the Rh (D, C, E, c, e, Cw ), Kell (K, k), Duffy (Fya, Fyb),Kidd (JkaJkb), Lewis (Lea, Leb), P, MNS (M, N, S, s), Lutheran (Lua, Lub) and Xg blood group systems. . Antibody screening is done in the standard immunohematology lab which also participates in EQAS (external quality assessment scheme) program in immunohematology and follows the AABB (American Association of Blood Banking) guidelines for immunohematology testing.

A commercially available 3 cell antigen panel was used for the antibody screening procedure where25µL of the patient's serum was mixed with50 µLred cells using low ionic strength saline (LISS) Coombs gel card. The cards were incubated at 37 degree C for 15 min and then centrifuged for 10 minutes. Look for agglutination. If antibody screening with the 3-cell antigen panel was positive, an extended 11-cell antigen panel was used for antibody identification in LISS.

A polyspecific direct antiglobulin test was performed on all patients using 0.8% patient's red cell suspension and LISS Coombs gel cards.

Results

A total of 55 transfusion dependent ß thalassemics were included in this study out of which 30 (54.55%) were males and 25(45.45%) females with a male to female ratio of 1.2: 1.

(Table 1). Mean age of patients included in the study was 8.23 years (age range: 6months - 16 years).

Mean weight and height of these patients were 20.96 ± 7.343 Kg and 117.34 ± 17.59 cm respectively. All the patients were receiving non leukoreduced packed red cell transfusion at an interval of 2-4 weeks. Twenty eight patients (50.9%) have been started on regular transfusion at before or at 1year of age. Four(7.27%) patients were of blood group A, 4(7.27%) were blood group AB, 18(32.73%) were blood group B and 29(52.73%) were blood group O. Fifty one (92.7%) patients were of Rh positive while 4 (7.3%) were of Rh negative blood group.

Total number of units of blood transfused ranged from 5units to 200 units (mean: 60.82 units).

Blood transfusion requirement during the previous year ranged from 102 ml/kg/yr to 222 ml/kg/yr (mean of 167.44ml/kg/yr).On peripheral smear examination, 52 (94.5%) patients showed features of thalassemia and 3(5.5%) were normal. The children with thalassemia who were adequately transfused have normal peripheral smear as ineffective erythropoiesis is suppressed. None of the peripheral smears were showing any features of significant hemolysis due to alloimmunization or autoimmunization.

None of the children were splenectomised.

Red Cell Alloantibodies

Out of 55 patients one patient developed alloantibody which was anti-K. Details of antibodies which were screened has been shown in Table 2. Transfusion details of the patient who has developed alloimmunisation has been mentioned in Table 3. All 55 patients were negative for Direct Coomb's Test.

Discussion

The development of red cell antibodies (both alloantibodies and autoantibodies) occurs in a variable number of multiply transfused thalassemia major patients. In majority of them, these antibodies are non-hemolytic; however, in some, they may be hemolytic. Fifty five patients were included in this study. These patients were transfused with nonleukoreduced ABO and RhD antigen matched blood. In this study we found an alloimmunization rate of 1.8% (one patient out of 55, who was positive for anti-K antibody) in beta thalassemics who were receiving regular nonleukoreduced packed red blood cell transfusion. This incidence is very low when compared to the various studies conducted worldwide.

Very few studies regarding alloantibody formation have been done so far in India. From the available literature, frequency of red cell alloimmunization ranges from 3.79% to 18.8 % in India. There is less disparity between the blood donor and patient population in- terms of ethnicity and hence the antigen status. This may be the reason for the lower alloimmunization rate in our study population. However we have not studied the frequency of minor red cell antigens in this population and that is the limitation of the study.

Some international reports showed wide variation in incidence of alloimmunisation following regular transfusion in thalassemics like 22.6% in a study by Spanos et al (9), 11% in a study by Coles(10) et al, Sirchia et al reported 5.2%(11), and Michail Merianou reported a frequency rate of 23.43%(12). Ameen et al in a study in Kuwait showed a higher frequency (30%) (13). Most of the available literature is from south east Asia and Mediteranean countries for the review as more reaearch is being done there.

Michail et al reported alloimmunization in two groups of children. One was the better-matched group which comprised of children who received blood matched for(compatible with) ABO, Cc, Ee, D and K antigens while the usual-match group received blood compatible with ABO and RhD antigen. They also found that the overall frequency of alloimmunization between the usual-match and better- match group was not statistically significant (12).

The factors responsible for high rate of alloimmunization in thalassemics are largely unknown. Various authors have observed a lower rate of alloimmunization in patients in whom transfusion was initiated at an early age. Spanos et al and Michail Merianou V et al have shown that alloimmunization rate was significantly lower in patients who started transfusion therapy before three years of age as compared to those who were started on transfusion later(9,12). Singer et al. reported a higher incidence of alloimmunisation among thalassemics who were splenectomised which was attributed to the absence of an efficient filtering of damaged or senescent red cells which may explore new antigens(1). Further, the total number of transfusions is also expected to have an effect on frequency of alloimmunisation (18).

Even though some earlier studies have shown some correlation between development of red cell alloimmunisation and factors like age at initiation of transfusion, splenectomy status, type of blood product transfused and number of units of blood transfused, in this study we were not able to analyze such correlation in view of the low incidence.

Conclusions

Frequency of red cell alloimmunization in this study was found to be 1.8%. None of the patients developed red cell autoimmunization. In most of the hospitals across our country, blood is provided to these children after ABO-Rh grouping and IAT cross-match and other antigens are not tested for. Since the development of alloantibodies in multi transfused thalassemics is a well recognized phenomenon and most of the common alloantibodies being directed against the Rh, Kell, Duffy and Kidd blood group systems, it would be ideal if phenotypically matched blood (for at least for Rh, Kell, Duffy and Kidd) can be provided to these patients who are receiving chronic blood transfusions.