Page 2565 - Hematology_ Basic Principles and Practice ( PDFDrive )

2288 Part XIII Consultative Hematology

hypovolemia. However, in nonimmune patients and in pregnant TABLE UK Donor Selection Guidelines for Donors at Risk of
women, blood transfusion must be accompanied by careful hemody- 158.3 Transmitting Malaria
namic monitoring to avoid precipitating or exacerbating pulmonary
edema. A recent randomized clinical trial showed that red cell longer- Donor Risk Category Guidelines
storage RBC units are not inferior to shorter-storage RBC units for Resident Defined as having lived in sub-Saharan Africa
tissue oxygenation as measured by reduction in blood lactate levels (except South Africa) or Papua New Guinea
and improvement in cerebral tissue oxygen saturation among children for a continuous period of 6 months at any
with severe anemia. 124 time of life
Whatever clinical guidelines emerge, in reality blood transfusion Permanent deferral unless malaria antibody test
in the heartland of malaria-endemic areas is beset by many practical results are negative at least 6 months after
and theoretic problems. First, the absence of well-characterized donor returning from a malarious area
panels (and thus systematic blood collection) frequently jeopardizes Any subsequent visits to any malarious area
the supply of blood. Second, even when standard screening for each require a 6-month deferral period and
human immunodeficiency virus (HIV) is in place, the residual risk negative antibody test results before
for HIV transmission in the serologic window of infectivity remains reinstatement
at 1 in 2500 to 1 in 6000. At a practical level, positive indirect
antiglobulin test results in the setting of acute infection may make History of malaria Permanent deferral unless malarial antibody test
the exclusion of alloantibodies difficult. Depending on the clinical results are negative at least 3 years after
urgency and transfusion history, the least serologically incompatible cessation of treatment or last negative test
blood may have to be given. results
One therapeutic option available in North America and in Europe Undiagnosed While abroad or within 4 weeks of return
for the urgent treatment of nonimmune patients with severe disease febrile illness Deferral for 12 months or 6 months if malarial
would be an exchange blood transfusion. This procedure removes antibody test results are negative
nonsequestered, infected erythrocytes and possibly circulating toxins. All other risks Deferral for 12 months or 6 months if malarial
In the absence of evidence from trials for the use of exchange transfu- antibody test results are negative
sion in malaria, some have suggested that this treatment could be
given for hyperparasitemia (>20%) in severely ill nonimmune
patients. 125,126 The salient features that make this clinical problem a and that significant immunity to falciparum malaria may be acquired
major public health concern are the very large numbers of children by residence after 6 months in a malarious area.
affected and the difficulty of satisfactory treatment by blood transfu- The criteria also require that residents, as well as those having had
sion outside specialist centers. malaria or an undiagnosed febrile illness, may be reinstated , after six
months without malaria or a fever that could have been due to
malaria or three years after treatment for an episode of malaria, if
Malaria as a Transfusion-Transmitted Infection antimalarial antibodies cannot be detected. The importance of anti-
malarial antibody testing rests on the fact that it is a very sensitive
Malaria is undoubtedly the most common transfusion-transmitted method to detect chronic infection, whereas the identification of
infection in the world. In endemic areas a large proportion of adult circulating malarial antigens or nucleic acids or microscopy would
donors will be parasitemic, perhaps 20% to 80%, depending on the fail to detect a level of 1 parasite/mL, which would still give a highly
rate of transmission. Here donor deferral is impractical, and treat- infectious dose in a unit of blood.
ment of recipients with a course of effective antimalarials is the most The assays for antimalarial antibodies previously used indirect
practical alternative. In nonendemic areas, transmission of malaria is immunofluorescence antibody tests (IFATs) to detect reactivity to a
an occasional but potentially devastating complication of blood crude parasite lysate as a target antigen. However, an enzyme-linked
transfusion, and considerable thought and resources are required to immunosorbent assay (ELISA) using recombinant malarial antigens
combat the problem effectively. has proved to be a more practical if slightly less sensitive alternative
The first case of transfusion-transmitted malaria (TTM) was in to IFATs. 131,134,135 These tests detect antimalarial antibodies in less
127
1911. Between 1911 and the mid-1970s the incidence of TTM than 2% of donors who have visited endemic areas. It has been cal-
rose to more than 140 cases per year, with P. vivax the most common culated that the return of 90% of malarial antibody–positive visitors
species causing infection, although the proportion of cases from P. to the donor pool releases an extra 50,000 units per year in the United
falciparum has steadily increased, perhaps reflecting the speed and Kingdom, and this is a highly cost-effective process to reduce the
destination of international travel. It is striking that the background attrition of eligible blood donors. In the United States, over 200,000
problem, namely malaria in returned travelers, is much more common donors per year are deferred after travel to malaria-endemic areas.
in the United Kingdom than in the United States, with the per capita Donor deferral is based on the potential of a donor to carry malaria
incidence differing by nearly a factor of 10 and a higher proportion and is therefore based on the area of travel, length of stay or residence,
of cases from P. falciparum in Europe and the United Kingdom elapsed time since leaving the endemic area, and history of malaria. It
compared with the United States. 128 has been repeatedly shown that application of even the most thorough
Recent experience in the United Kingdom and the United States donor questionnaires allows some of those carrying malaria to give
has emphasized the seriousness of TTM. Two of the last five cases of blood because guidelines are frequently incorrectly applied or ques-
malaria owing to blood transfusion in the United Kingdom were tions are answered inaccurately in routine practice. 133,136
fatal. 129–131 In the United States, 14 cases of TTM were reported In Canada donors reporting diagnosis or treatment of malaria
between 1990 and 1999, but only 5 cases were reported between defer permanently, and in the United States donors are deferred for
133
2000 and 2009. 132,133 Detecting these cases after transfusion is fre- 3 years after treatment. The criteria will inevitably cause unneces-
quently delayed because malarial infection acquired in nonendemic sary deferral of those who never actually had malaria but also permit
countries rarely figures in immediate differential diagnosis and some individuals with low-level chronic infection to donate because
requires careful examination of the blood film. malaria not infrequently presents more than 3 years after travelers
The mainstay of preventing TTM in the United Kingdom is return from endemic areas. 132,133 The last case of malaria transmitted
donor deferral backed up by detection of circulating antibodies to in the United Kingdom was by someone who had left a malarious
malaria antigens. The guidelines for donor deferral were carefully area 8 years previously, and the longest recorded case of recrudescence
134
revised after analysis of circumstances of recent TTM (Table 158.3). of malarial infection is 44 years for P. malariae.
These criteria recognize that malaria in the nonimmune patient is Permanent deferral of all those visiting malaria-endemic areas is
likely to present within 6 months of return from an endemic area unlikely to be a viable strategy to prevent TTM because donor bases