Screening and diagnosis of Hb Quong Sze [HBA2: c.377T > C (or HBA1)] in a prenatal control program for thalassemia.

Hb Quong Sze [Hb QS, HBA2: c.377T > C (or HBA1)] is a common nondeletional thalassemia in southern China. It is one of the major alleles causing nondeletional Hb H (β4) disease in the Chinese population. There is no strategy currently in place that aims to screen using hematological index cutoffs for this variant. This study was carried out to evaluate whether it is effective to use mean corpuscular hemoglobin (MCH) <27.0 pg as a screening test in the first step of screening for Hb QS carriers in southern China. The data of hematological testing in the Hb QS carriers obtained from couples who underwent prenatal thalassemia screening, regardless of the red blood cell (RBC) indices, were retrospectively reviewed. A total of 51 Hb QS carriers were identified, giving a prevalence rate of 0.2%; among these, 45 were Hb QS heterozygotes. The values of hemoglobin (Hb), MCV and mean corpuscular Hb (MCH) in the 45 Hb QS heterozygotes were 13.2 ± 1.8 g/dL, 75.2 ± 3.3 fL and 24.5 ± 0.5 pg, respectively. Eight heterozygotes (17.8%) had an MCV value of >80.0 fL, ranging from 80.9 to 84.1 fL, and would not be detected using the cutoff value of MCV <80.0 fL as a criterion for thalassemia screening. However, if screening had been based on the MCH <27.0 pg value, all 45 Hb QS heterozygotes would have been detected. Using a cutoff value of MCH <27.0 pg in nondeletional thalassemia screening would greatly decrease the DNA diagnosis burden.