rev bras hematol hemoter. 2 0 1 5; 3 7(5) :287–289
www.rbhh.org
Revista Brasileira de Hematologia e Hemoterapia
Brazilian Journal of Hematology and Hemotherapy
Scientific Comment
The importance of hemoglobin A
2
determination
Maria Stella Figueiredo
*
Universidade Federal de São Paulo (UNIFESP), São Paulo, SP, Brazil
a r t i c l e i n f o
Article history:
Received 24 June 2015
Accepted 7 July 2015
Available online 21 July 2015
Hemoglobin (Hb) A
2
(
2
2
) constitutes less than 3% of the total
hemoglobin (Hb) in adults and has almost no physiological
importance.
1
On the other hand, the determination of Hb A
2
is an important tool to diagnose the beta-thalassemia trait
(BTT).
1,2
Although individuals with BTT do not need treat-
ment, the accurate detection of the carrier state is important
in genetic counseling to determine risk of having a child with
a major disease.
3
Elevated levels of Hb A
2
and microcytosis are suggestive
of the diagnosis of BTT. However, BTT may be present with
normal levels of Hb A
2
as a few cases of -thalassemia are
not associated with elevated Hb A
2
, and because of the asso-
ciation of BTT with iron deficiency or with -thalassemia
(-Thal).
1,2,4–6
There are many other factors, inherited or
acquired, that can interfere in Hb A
2
levels (Table 1).
3,4
Hb A
2
can be measured by several laboratorial methods, but
these methods have differences in accuracy.
7
Cation exchange
high performance liquid chromatography (HPLC), microcol-
umn chromatography, and cellulose acetate electrophoresis
with elution are considered acceptable methods to diagnose
BTT, whereas cellulose acetate electrophoresis followed by
scanning densitometry is not.
2
The accuracy of cellulose
acetate electrophoresis with elution depends on the train-
ing and experience of the laboratory technician who performs
See paper by Fonseca et al. on pages 296–301.
*
Correspondence to: Hematology and Blood Transfusion Division, Escola Paulista de Medicina, Universidade Federal de São Paulo
(UNIFESP), Rua Dr. Diogo de Faria, 824, 0437-002 São Paulo, SP, Brazil.
E-mail address: stella.figueiredo@unifesp.br
the test, and microcolumn chromatography can give problems
with co-elution of some Hb variants.
7
Recent studies have confirmed the higher quality of auto-
mated HPLC in the measurement of Hb A
2
compared to the
other methods,
8,9
which is why this has become the method
of choice. On the other hand, in automated HPLC, the mea-
surement of Hb A
2
is inaccurate when Hb S is present.
2,3,10
As the amount of Hb S is related to the degree of inaccuracy,
levels are higher in patients with sickle cell anemia (SCA) or
Hb S/-thalassemia (S-Thal) than in sickle cell trait.
2
Thus,
the amount of Hb A
2
does not indicate BTT when Hb A and
beta gene variants are found together.
11
Furthermore, when
beta gene variants are present without Hb A, the diagnosis of
concomitant BTT is not necessarily associated to the elevation
of Hb A
2
and so further investigations using family studies or
DNA analysis are necessary.
10
As mentioned above, -Thal is capable of interfering in the
determination of Hb A
2
.
4
Individuals with the
0
-thalassemia
trait or homozygous for
+
-thalassemia have lower levels of
Hb A
2
, but the influence of the coinheritance of -Thal and
BTT on Hb A
2
levels is uncertain.
6
In Brazil, the incidence of -Thal varies from 0.11 to 0.22%
depending on the geographical region studied.
12–15
It is well
known that the association of -Thal and SCA is common in
http://dx.doi.org/10.1016/j.bjhh.2015.06.002
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