Consideration of immunochromatographic strip positive results for screening of alpha-thalassemia in elevated hemoglobin F samples

The screening test for early detection of α-thalassemia is essential in effective management and genetic counseling. The immunochromatographic (IC) strip test is widely used for α-thalassemia screening due to its simplicity and high sensitivity. This study explores the causes of false-positive IC strip results in subjects with HbF >5% who tested negative for common α⁰-thalassemia --^SEA, --^Thai and --^{Chiang Rai} type deletions. Fifty whole blood samples were tested using IC strips, and resulting positive samples were retested with washed red blood cells (RBCs) and plasma. Follow-up testing included molecular analysis to detect common hemoglobinopathies in washed RBCs, including α⁺-thalassemia -α^3.7 and -α^4.2 deletions, Hb Constant Spring (CS), Hb Quong Sze (QS) and Hb Westmead (WM), as well as antinuclear antibodies (ANAs) screening in plasma. Ten of 50 EDTA whole-blood samples tested positive using the IC strip test, with eight showing positivity in plasma and seven in washed RBCs. Among them, one plasma-positive sample was also positive for ANA, suggesting potential antibody interference. Of the seven RBC-positive samples, three had common hemoglobinopathies: two with the -α^3.7 deletion and one with Hb CS. The remaining four RBC-positive cases had no detectable mutations but were infants under three months of age. Since most false positives occur in infants under 8 months, caution is recommended when testing this age group. Additionally, washing red cells can help reduce antibody interference. Further molecular studies, such as Sanger sequencing, MLPA and NGS, should be initiated in cases without obvious causes.