RBC Measurements and Genotype in a-Thalassemia Trait
Measurements of Red Cell Parameters in a-Thalassemia Trait:
Correlation With the Genotype
CHEN WANG, LISA BEGANYI, BERNARD J. FERNANDES
Laboratory Hematology 6:163-166
©2000 Carden Jennings Publishing Co., Ltd.
Microcytosis, a common finding in the complete blood count, often
requires further investigation to determine its cause. a-Thalassemia
trait constitutes a significant proportion of patients with
microcytosis. In this study, we looked at the red blood cell (RBC)
parameters found in patients with a-thalassemia trait and evaluated
the correlation of these parameters with the various genotypes of
a-thalassemia trait. A total of 96 adult patients were confirmed to
have a-thalassemia trait on the basis of genotyping, and were assigned
into 3 groups, including 39 patients with a single gene deletion
(-a/aa), 33 with the trans type 2 gene deletion (-a/-a), and 24 with
the cis type 2 gene deletion (--/aa). A comparison of RBC indices
showed a correlation between the degree of microcytosis and the number
and type of gene deletions. The --/aa genotype was associated with the
lowest mean corpuscular volume (MCV), followed by the -a/-a genotype
and then the --a/aa genotype. The RBC count showed the reverse trend
among the 3 groups. Most of the patients with the --/aa genotype (79%)
had positive results for the hemoglobin H inclusion body test, but
virtually all patients with -a/aa or -a/-a genotypes had negative
results for this test. It is particularly important to identify
patients who have the --/aa genotype, because these patients are at
risk for producing offspring with clinically serious thalassemia. The
finding that the --/aa genotype was associated with a lower MCV and
higher RBC count than the other 2 genotypes, and that most of those
with the --/aa genotype had readily detectable hemoglobin H inclusions
in the RBCs, may have practical application in the differentiation of
--/aa from the other genotypes, particularly when genotyping is
unavailable.
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 6.3.Wang
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