Determination of mean corpuscular haemoglobin cut-off point for differentiating alpha plus and alpha zero thalassaemia in thalassaemia screening

This study assesses haematological parameters as screening tools for identifying α zero (α⁰) thalassaemia candidates for DNA analysis. The Malaysia Thalassaemia Diagnosis Code (MTDC) uses mean corpuscular haemoglobin (MCH) < 25 pg to screen for suspected α⁰ thalassaemia carriers. Six haematological parameters from 304 cases genotyped by Gap-Polymerase Chain Reaction or Multiplex Ligation-dependent Probe Amplification were analyzed. Among the cases, 160 individuals (52.6%) were α+ thalassaemia silent carrier (-α/αα), comprising heterozygotes for -α3.7, -α4.2, –(α)20.5 and -α2.4. Twelve individuals (3.9%) were α+ thalassaemia carrier (-α/-α), including homozygous -α3.7 and compound heterozygous -α3.7 and -α4.2. Meanwhile, 111 individuals (36.4%) were α0 thalassaemia carrier (--/αα) consisting of heterozygotes for --SEA, --GB, --FIL, --AW, and –THAI deletions. Deletional Hb H disease (--/-α) was observed in individuals with compound genotypes such as -α3.7/--SEA, -α3.7/--GB, -α3.7/--AW, -α4.2/--SEA and -α2.4/--SEA. All parameters correlated with the number of α-globin gene deletions, with mean corpuscular volume (MCV) (r2 = 0.73) and MCH (r2 = 0.77) showing the strongest associations. Gender-specific MCH cut-offs of < 22.65 pg for males and < 22.25 pg for females demonstrated excellent diagnostic performance, with higher sensitivity and specificity in females (90.3% and 93.9%) than in males (89.5% and 88.9%). The findings indicate that the currently used MCH cut-off of 25 pg may be higher than optimal for identifying α⁰ thalassaemia carriers. A lower MCH threshold improves detection performance and may support refinement of the MTDC screening criteria to better prioritize high-risk individuals while reducing unnecessary DNA testing among α⁺ thalassaemia cases.