Anti-ζ Antibody Screening for α-Thalassemia Using Dried Filter Paper Blood

Abstract

The most common α-thalassemia in Southeast Asian or Southern Chinese populations is the (- -^SEA) double α-globin deletion. Couples heterozygous for (- - ^SEA) have 25% risk for hydrops fetalis from loss of all four α-globin genes. The (- -^SEA) deletion spares the embryonic ζ-globin genes and causes traces of ζ-peptide to persist throughout life. A colorimetric monoclonal anti-ζ antibody test for raised ζ-peptide has detected the (- -^SEA) deletion in liquid blood samples, but not deletions of the entire α-globin region with loss of the ζ-globin genes. Eluates from dried blood spots had the same anti-ζ antibody color reaction as whole blood, even after storage at 4°C for up to 77 days. The anti-ζ antibody test was positive in 24 of 91 microcytic samples (mean corpuscular hemoglobin <24 pg), including four with iron deficiency; it was negative in 26 provisionally diagnosed α-thalassemia-1 heterozygotes and all 32 nonmicrocytic samples. Southern blot analysis and a specific SEA-polymerase chain reaction test confirmed that 18 anti-ζ antibody-positive samples and 1 anti-ζ antibody-negative sample had the (- -^SEA) deletion. Two anti-ζ antibody-negative microcytic samples had the (- -^Fil) total α-globin region deletion, 2 had single α-gene deletions, 22 others may also have had a total α-region deletion. Hence specificity was very high and sensitivity was 95%. The anti-ζ antibody test can detect the (- -^SEA) deletion in dried blood samples, even after prolonged storage. This simple inexpensive test can conveniently screen samples collected at a distance from a central laboratory.