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Letters |
a Author for correspondence. Fax 32 2 555 66 55; e-mail fcotton{at}ulb.ac.be
Department of Clinical Chemistry, Hôpital Erasme, Université Libre de Bruxelles, 808 Route de Lennik, B1070 Brussels, Belgium
To the Editor:
We read the letter from Dr. Dash with interest (1),
but we do not agree with her demonstration. We use the same
cation-exchange HPLC (Bio-Rad Variant) as Dr. Dash, and we have
concluded that hemoglobin (Hb) A2 cannot be
quantified in the presence of Hb D by this method. As shown on Fig. 1
, an incomplete return to baseline between the Hb
A2 and Hb D peaks does not allow accurate
integration of Hb A2. To confirm this
observation, we compared the Hb A2 values
obtained by HPLC and anion-exchange microchromatography (Quik-Sep;
Isolab) in nine samples from Hb D heterozygotes. The latter method
separates hemoglobins on the basis of their pI, and the Hb
A2 measurement is not influenced by Hb S or Hb D
but is influenced by Hb C, Hb E, or Hb O (2). When
anion-exchange chromatography was used, all results (mean, 2.6%;
range, 2.4–2.9%) were within the reference interval (2.0–3.5%),
whereas those obtained with HPLC were somewhat lower (mean, 1.8%;
range, 1.2–2.0%). It has been shown that these methods give similar
results in patients without hemoglobin variants
(3)(4). In our opinion, the low Hb
A2 values measured by HPLC are most probably
attributable to integration problems only. The Hb
A2 values measured by a specific method seem
similar in Hb D heterozygotes and Hb A homozygotes.
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To detect ß-thalassemia carriers, a precise and specific method for Hb A2 measurement is needed. This is not the case with HPLC in Hb D heterozygotes or in Hb S heterozygotes (3)(4). In these cases, another method is required, such as anion-exchange chromatography or capillary electrophoresis (4), which in turn are not suitable in the presence of Hb C, Hb E, or Hb O. This illustrates that each laboratory should have an alternative method adapted to each case and keep in mind the performances of each method.
References
Salmaniya Medical Complex, P.O. Box-12, Bahrain, Fax 973-279649
a Author for correspondence. Fax 32 2 555 66 55; e-mail fcotton{at}ulb.ac.be
To the Editor:
I am glad to note that Cotton et al. have corroborated our observation of low hemoglobin (Hb) A2 values in Hb D cases when measured by HPLC (Bio-Rad Variant).
Our documentation was to emphasize the unreliability of Hb A2 measurements by this method in the presence of abnormal hemoglobins because the value not only can be spuriously increased, as in Hb S cases, but may also be decreased, as in Hb D cases. Thus, additional methods are required to quantify Hb A2 in the presence of abnormal hemoglobins.
The following articles in journals at HighWire Press have cited this article:
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  T. N. Higgins, A. Khajuria, and M. Mack Quantification of HbA2 in Patients With and Without {beta}-Thalassemia and in the Presence of HbS, HbC, HbE, and HbD Punjab Hemoglobin Variants: Comparison of Two Systems Am J Clin Pathol, March 1, 2009; 131(3): 357 - 362. [Abstract] [Full Text] [PDF]
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 K. Zurbriggen, M. Schmugge, M. Schmid, S. Durka, P. Kleinert, T. Kuster, C. W. Heizmann, and H. Troxler Analysis of Minor Hemoglobins by Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry Clin. Chem., June 1, 2005; 51(6): 989 - 996. [Abstract] [Full Text] [PDF]
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G. M. Clarke and T. N. Higgins Laboratory Investigation of Hemoglobinopathies and Thalassemias: Review and Update Clin. Chem., August 1, 2000; 46(8): 1284 - 1290. [Abstract] [Full Text] [PDF]
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