A Novel and Rapid Assay for Sickle Cell Disease Screening
Children born with sickle cell disease in low-resource regions of the world often remain undiagnosed and therefore do not receive appropriate treatment.
A novel diagnostic immunoassay may present a rapid and affordable point-of-care option for screening newborns in low resource countries for sickle cell disease (SCD), according to a report published in the American Journal of Haematology.
Though over 90% of children with SCD are born in sub-Saharan Africa and central India, up to 90% of these children do not receive a diagnosis and die before reaching 5 years of age. Most screening programs for SCD are limited by cost, lack of adequate laboratory infrastructure, or lack of sustained funding.
HemoTypeSC is an immunoassay that detects hemoglobins A, S, and C sing monoclonal antibodies. The test requires only 1.5 µL of blood and has an end-user cost of less than $2 per test. In this blinded, multicenter, prospective diagnostic accuracy study, researchers collected blood from a total of 587 patients from low- (Ghana; 383 patients), medium- (Martinique; 46 patients), and high-resource (United States; 158 patients) countries. The blood was tested with HemoTypeSC, and the resulting diagnoses were confirmed by gel electrophoresis in Ghana, isoelectric focusing in Martinique, or capillary zone electrophoresis in the United States.
Primary outcomes included determining sensitivity, specificity, and positive and negative predictive value of HemoTypeSC in detecting HbA, HbS, and HbC in trait and disease states.
HemoTypeSC demonstrated both sensitivity and specificity of 100% for detecting HbA, and sensitivity and specificity were greater than 99% for detection of both HbS and HbC. Across all Hb phenotypes, HemoTypeSC demonstrated accuracy of 99.5%. The assay identified every HbSS and HbCC phenotype, 499 of 501 HbAA, HbAS, or HbAC phenotypes, and 31 of 32 HbSC phenotypes.
The authors noted that one limitation of HemoTypeSC is its qualitative nature, which means certain Hb phenotypes are indistinguishable by the assay. For example, HemoTypeSC would return a result of sickle cell trait for both sickle-beta-positive-thalassemia and HbS trait because HbA and HbS are both present in both cases. However, these limitations are present in other previously published point-of-care Hb screening devices as well.
HemoTypeSC does not require instrumentation, electricity, or refrigeration, making it a promising diagnostic tool “that can be used in resource-limited regions with a high prevalence of SCD to provide timely diagnosis and support newborn screening programs,” the authors concluded.
Steele C, Sinski A, Asibey J, et al. Point-of-care screening for sickle cell disease in low-resource settings: A multi-center evaluation of HemoTypeSC, a novel rapid test [published online October 5, 2018]. Am J Haematol. doi: 10.1002/ajh.25305