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目的 :确定血红蛋白 A2 (Hb- A 2 )在α地中海贫血和β地中海贫血 (地贫 )诊断中的临界值 ,并进行敏感性、特异性和准确性的评估。方法 :采用同步盲法对 383例门诊例行产检的育龄夫妇进行 Gap- PCR、反向斑点杂交基因(RBD)诊断和 Hb- A2的定量测定。 Gap- PCR确诊的α地中海贫血 2 4 6例 ,其中α地中海贫血杂合子 12 2例为病例组 ,12 4例正常者为对照组。 RBD确诊的β地中海贫血 135例 ,其中 10 0例β基因缺陷的杂合子为病例组 ,35例正常者为对照组。确定最适合的临界值 ,并进行准确性、敏感性、特异性、阳性似然比、阴性似然比评估。结果 :诊断α地中海贫血 Hb- A 2最适临界值为≤ 2 .3% ,敏感性 5 9.8% ,特异性 5 7.3%。诊断β地中海贫血最适临界值为≥ 3.8% ,其敏感性为 95 % ,特异性77.1%。Hb- A2的受试者工作曲线显示 Hb- A2在β地中海贫血诊断时曲线下面积大于α地中海贫血诊断时的曲线下面积。结论 :Hb- A 2在α地中海贫血筛查时临界值为≤ 2 .3% ,在β地中海贫血筛查中为≥ 3.8%。 Hb- A2的含量变化对β地中海贫血基因缺陷的敏感性和特异性较高 ,对α地中海贫血基因缺失的敏感性和特异性稍低
OBJECTIVE: To determine the critical value of hemoglobin A2 (Hb-A2) in the diagnosis of alpha thalassemia and beta thalassemia (thalassemia) and evaluate its sensitivity, specificity and accuracy. Methods: Gap-PCR, reverse dot blot hybridization (RBD) diagnosis and quantitative determination of Hb-A2 were performed in 383 pregnant women of childbearing age who were routinely diagnosed at the outpatient department by synchronous blind method. There were 246 cases of α-thalassemia confirmed by Gap-PCR, in which 122 cases of α-thalassemia heterozygote were case group and 124 cases were control group. RBD diagnosed 135 cases of β-thalassemia, 10 cases of β-gene defect heterozygotes for the case group, 35 cases of normal control group. Determine the most appropriate cut-off value, and the accuracy, sensitivity, specificity, positive likelihood ratio, negative likelihood ratio assessment. Results: The optimal cutoff value of Hb-A 2 in diagnosing α-thalassemia was ≤ 2.3%, sensitivity 5.8%, and specificity 7.33%. The optimal threshold for diagnosis of β-thalassemia is ≥ 3.8% with a sensitivity of 95% and a specificity of 77.1%. Subject curves for Hb-A2 show that the area under the curve for Hb-A2 at diagnosis of beta-thalassemia is greater than the area under the curve at diagnosis of alpha-thalassemia. CONCLUSIONS: The cut-off value of Hb-A2 at alpha thalassemia screening is ≤ 2.3% and ≥ 3.8% in β-thalassemia screening. The change of Hb-A2 is sensitive and specific to the gene defect of β-thalassemia, and has a lower sensitivity and specificity to the gene deletion of α-thalassemia