Application of retinol-binding protein enzyme immunoassay to dried blood spots to assess vitamin A deficiency in a population-based survey: The Uganda Demographic and Health Survey 2006

Background. Vitamin A deficiency is a public health problem in most developing countries. The technological challenges associated with the measurement of serum retinol have limited the epidemiologic assessment, of vitamin A deficiency. The combination of retinol-binding protein (RBP) enzyme immunoassay and dried blood spots offers a rapid, inexpensive, and reliable tool for the population-level assessment of vitamin A deficiency in resource-poor settings. Objective. To report on the application of RBP enzyme immunoassay and dried blood spots to assess serum retinol concentrations as an indicator of vitamin A status in the Uganda Demographic and Health Survey 2006. Methods. A total of 5,642 capillary blood spot samples were collected by fingerprick onto filter paper cards from women (15-49 years) and children (6-59 months) in a representative probability sample of 9,864 households between May and October 2006. The cards were dried, packed individually with desiccant, and kept at 4 degrees C in a portable refrigerator in the field and at -20 degrees C in the laboratory. Prior to analysis, the RBP enzyme immunoassay was optimized with the use of matched serum and dried blood spots. Results. The correlation between RBP values determined by matching serum and dried blood spots was excellent (r = 0.79, p <.00001). The prevalence of vitamin A deficiency in women (RBP < 1.24 mu mol/L) and children (RBP < 0.825 mu mol/L) was 19.4% and 20.4%, respectively. Conclusions. The combination of RBP enzyme immunoassay and dried blood spots is a simple, reliable, and cost-effective tool for the estimation of vitamin A deficiency in population-level surveys in resource-poor settings.