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Etiology of anemia of blood donor candidates deferred by hematologic screening
Rev Bras Hematol Hemoter. 2012;34(5):356-60
the instructions of the kit, errors of up to 5.0% are permissible,
which in the case of male (13.0 g/dL) and female (12.5 g/dL)
donors corresponds to 0.7 g/dL and 0.6 g/dL, respectively. These
differences, based on the specifications of the instructions, do not
characterize failure of the technique employed and are in accordance
with the study of Rosenblit et al.
(16)
who found a difference of 0.6
g/dL between two automated techniques. Research carried out in
Northern England, employing the copper sulphate precipitation
technique to screen blood donors also observed differences between
tests of 0.24 for men and 2.8 for women
(17)
. It is recommended that
the variations should not exceed 0.3 g/dL when employing the
cyanmethemoglobin method
(18)
.
It is interesting that 38.1% of individuals considered
unsuitable by the finger prick technique, would have been
considered fit by the automated technique using a sample obtained
by venipuncture. These findings reinforce the need for stringent
controls and periodic evaluations of the screening technique as,
with this false positive rate, if extrapolated to the total number
of individuals excluded for anemia every year in Brazil, would
represent the inclusion of approximately 40,000 donors.
The general index of iron deficiency in the tested blood donor
candidates (anemic and non-anemic) was 20.5% with a slightly
higher prevalence in men (25.0%) than in women (18.9%), and
significantly higher in the Anemic Group, for both genders as
expected. Iron deficiency was responsible for anemia in 37.5%
of the Anemic Group. The worryingly high iron deficiency rate
observed in this study was similar to the result found in 348 male
and female blood donors in Port Harcourt in Nigeria (20.6%)
(19)
– a country in worse economic conditions than Brazil - and much
higher than the results of a study carried out in the blood bank of
Santa Casa de São Paulo
(1)
, in which 11% of 300 blood donors
of both genders had iron deficiency
(5)
, and in an Iranian study of
male blood donors (14.1%)
(20)
. However, alarming results on iron
deficiency were also found in a North American study on repeat
donors in which two-thirds (66%) of women and almost half of
men (49%) had iron deficiency
(4)
.
The fact that the non-anemic individuals in this study presented
ferritin levels higher than anemic candidates, although expected,
reinforces the importance of this test in the propedeutics of anemic
donors. In addition, identifying non-anemic donors with low levels
of ferritin (10.6%) should be the reason for prompt intervention
to prevent anemia; this supports the position of some authors
who suggest that ferritin should be measured in the screening of
donors
(19-23)
, particularly those who donated more than five times
(5,19)
as well as iron supplementation for iron deficiency
(24,25)
.
Studies have shown that ferritin levels drop with the number
of donations
(2,5,6,20)
and the greater frequency in male and female
donors than in individuals who are not donors
(5)
. In this study, the
ferritin levels dropped parallel to the number of donations with
more consistent declines being observed in individuals who made
six or more donations when compared to those who donated
less than six times, thus proving the influence of the number of
donations on serum ferritin levels.
Besides iron-deficiency anemia, beta thalassemia was
identified as a possible cause of anemia in 9.3% of the anemic
individuals in this study. Elevated Hb A2 was also found in
7.2% of the candidates in the Non-anemic Group even though
they did not present with anemia. Published data show that beta
thalassemia varies between regions and that heterozygosity
for thalassemia is responsible for the greatest difficulty of
diagnosing anemia followed by rare variants, and interactive
forms of hemoglobinopathies
(26,27)
. A study of the etiology of
anemia in 58 patients without iron deficiency and 235 controls
demonstrated that 32.8% of the patients and 0.9% of the
controls were beta thalassemia carriers
(28)
. Hence, our findings
of 7.2% of individuals in the Non-anemic Group with suspicion
of beta thalassemia are well above what would be expected.
However, researchers recommend caution when diagnosing
beta thalassemia only by the dosage of Hb A2. They point out
that elevated levels can also be detected in other acquired and
congenital conditions and suggest repeating the test before
arriving at any diagnostic conclusion
(7,29)
. Thus, we recommend
further studies to confirm these findings.
The results demonstrated evidence of a high rate of deferral
of donors due to anemia, and the discrepancies observed between
the manual screening technique used and automated screening
suggest the need for standardization, constant control of the
hematological screening technique employed and confirmation
of hematimetric levels before deferring a candidate due to
anemia. Iron deficiency has been confirmed as the leading
cause of deferral of blood donor candidates due to anemia; this
increases as the number of donations increases suggesting that the
measurement of ferritin levels should be included in the screening
process, especially after multiple donations and for individuals
with hematimetric levels close to cut-off limits. Additionally,
iron supplementation should be provided to all repeat donors and
donors with hemoglobin or hematocrit levels below or even near
to the normal cut-off limit.
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