Do we need to test blood donors for sickle cell anaemia?

Abstract

The case reported here by Lippi G et al1 is very timely and perhaps needs wider reflection. Sickle cell Anaemia is mostly found in Sub-Saharan Africa and in the South Mediterranean regions. Epidemiological studies have demonstrated that a strong link exists between the presence of SCA and malaria. The presence of sickle haemoglobin offers a natural advantage against malaria infection, as Plasmodium Falciparum is less likely to multiply within the abnormal erythrocytes. However, when the sickle haemoglobin (HbS) is inherited homozygously, the subjects may suffer severe vaso-occlusive events (sickle cell crises) which over time will contribute to multiple organ damage and reduced life expectancy2. Both homozygous and heterozygous subjects will survive up to reproductive age, ensuring the transmission of the genetic defect. On the other hand, subjects with normal haemoglobin pattern (HbAA) are very likely to die of malaria infection during childhood or even in utero (e.g. cerebral malaria). Sickle Cell Anaemia (SCA) remains, one of the most relevant diseases. According to the World Health Organisation (WHO), each year > 300,000 babies with SCA are born worldwide; the majority of them in the Third World. Moreover approximately 5% of the world’s population are carriers of SCA - the percentage of people who are carriers of the gene is as high as 25% in some regions3. Because SCA is mostly found in geographical areas with very poor socioeconomical conditions, migration of people carrying the gene or with the actual disease is a common and increasing finding. In this respect, SCA has to be considered as a global problem. In addition intraethnic marriages will ensure the penetrance of the abnormal gene within caucasian populations which historically were not affected. The screening of blood donors for SCA is therefore a relevant question. Though initially this should probably seem obvious, we should remember that in particular geographical areas (e.g. Nigeria) excluding people from donating on account of their ethnic background or their potential heterozygous SCA-carrier status (HbAS) is not possible, as it would severely impair blood bank stocks4 and would reduce the availability of donations with blood groups more common to the indigienous population (e.g. Fya, Fyb, etc). The main reasons for exclusion of donors with HbAS from donating is that in particular settings, (especially during surgery or prolonged hypoxaemia or in cases of pre-existing vaso-occlusive disease) vaso-occlusion may occur2. The majority of studies on this topic have been conducted on military recruits under hypoxic conditions, showing an increased risk of sudden death (28%)5. Similarly, a donation of sickle cell blood, could carry some risk for patients, though the literature on this seems unclear and contradictory. For instance, in a study on patients that received known sickle-cell trait blood (n=13), no adverse effects were reported6. A further issue has arisen with leukofiltration of units collected from donors with sickle haemoglobin. The filtration time is often prolonged7 on account of sickle cell polymerisation and the filtration process may even fail with the result that the amount of white blood cells in the final product is beyond that specified in various guidelines. These abnormalities are usually detected by quality control (QC) and such units are discarded. The possibility, however, of administering a unit with sickle cell blood cannot be fully excluded unless a specific test is performed (e.g. sickle cell dex). Finally it is relevant to note that no clear consensus exists on this topic and neither has the European Commission considered this issue in its European Blood Directive (Directive 2002/98EC). Awareness of this issue and possibly a set of guidelines may be necessary.