tailieunhanh - ANEMIAS AND OTHER RED CELL DISORDERS - PART 8

Thay thế amino acid trong hemoglobin S và C hemoglobin thay đổi các đặc tính phí của các phân tử để họ di chuyển khác nhau trong một điện trường hơn so với F hemoglobin A. Hemoglobin và hemoglobin A2 đều có mô hình di cư khác nhau từ hemoglobin A, | CHAPTER 13 I SICKLE CELL DISEASE 261 TABLE 13-3 IDENTIFICATION OF THE HEMOGLOBINS COMMON IN THE SICKLE CELL SYNDROMES Technique Positives Negatives Direct Quantification Time Use Availability Cellulose acetate electrophoresis Separates A S F C Not acceptable for A2. Poor F A S separation No 60 min High Citrate agar electrophoresis Clear separation of F from A S Not acceptable for A2 No 60 min High Isoelectric focusing Clear separation of F A S C Not acceptable for A2 Yes 45 min Low HPLC Identifies A S C F A2 None Yes 5 min Moderate PCR Identifies all common Hb variants useful for prenatal screening Relatively expensive Yes 30 min Low DIAGNOSIS OF SICKLE CELL DISEASE The amino acid substitutions in hemoglobin S and hemoglobin C change the charge characteristics of the molecules so that they migrate differently in an electric field than does hemoglobin A. Hemoglobin F and hemoglobin A2 each has different migration patterns from hemoglobin A S and C because of their structural differences. Nonetheless the various hemoglobins overlap in pattern depending on the electrophoretic technique. No single approach can provide complete identification of aberrant and normal hemoglobin in one fell swoop. The most commonly used approach to identification of aberrant hemoglobins is cellulose acetate electrophoresis at alkaline pH followed by citrate agar electrophoresis at acid pH when necessary. Table 13-3 summarizes this information. The amino acid substitutions in hemoglobin S and C also change size and biophysical characteristics of the molecules. High performance liquid chromatography HPLC takes advantage of these differences to separate the hemoglobin variants from hemoglobin A. The technique requires a very small amount of blood and much less time than the electrophoretic approaches. In contrast to electrophoresis HPLC also gives a quantitative readout of the relative hemoglobin content of a sample. HPLC is slowly displacing electrophoresis for the identification of common .