Validation of a rapid enzyme immunoassay for the quantitation of retinol-binding protein to assess vitamin A status within populations

Formerly of Program for Appropriate Technology in Health (PATH), Seattle, WA 98396, USA.
European Journal of Clinical Nutrition (Impact Factor: 2.71). 11/2006; 60(11):1299-303. DOI: 10.1038/sj.ejcn.1602456
Source: PubMed


To compare the prevalence of vitamin A deficiency (VAD) among Cambodian preschool children as determined by the retinol-binding protein-enzyme immunoassay (RBP-EIA) and direct measurement of serum retinol by high-performance liquid chromatography (HPLC).
Sera from 359 children were randomly selected from archived specimens collected in a national VAD prevalence survey in Cambodia.
Sera were first analyzed for retinol content by HPLC and then subjected to analysis using RBP-EIA to determine serum RBP concentrations. National Institute of Standards and Technology and control sera were used to ensure quality and accuracy for each set of analyses. To classify VAD, the same cutoff point of <0.70 micromol/l was employed for each indicator.
Overall, the prevalence of VAD based on serum retinol was 22.3% (95% confidence interval (CI): 18.0, 26.6), whereas the RBP-EIA indicated a VAD prevalence of 20.9% (95% CI: 16.7, 25.1). A simple linear regression model indicated an R2 of 0.79, and a receiver operating curve analysis revealed an area under the curve of 0.92.
We found no significant difference between the results of RBP-EIA compared to retinol analyzed by HPLC in estimating the prevalence of VAD. Use of the test could enable public health authorities to assess the extent of VAD and track progress in control programs in resource-poor settings.

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Available from: Patrick Racsa, Oct 16, 2014
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    • "The ability to accurately, but feasibly, assess vitamin A status in individuals and communities using responsive indicators is fundamental to quantifying the prevalence and severity of vitamin A deficiency, maintaining surveillance of a population over time, and evaluating programs. Although valid methods exist for research, there is an ongoing and urgent need to refine, simplify, and lower the cost and processing times required to assess population vitamin A status. Examples of recent developments that hold the potential for meeting program needs with further refinements in the future include the measurement of retinol-binding protein as a means to assess vitamin A status (Hix et al., 2006), collection and analysis of blood spots to determine the status of vitamin A and other micronutrients (Erhardt et al., 2004), and dark adaptometry (Congdon and West, 2002) which is presently undergoing further refinements to advance portability and reduce costs (Labrique A et al, personal communication, 2006). In terms of evaluating the impact of programs, it is likely that indicators for supplementation and fortification programs will be different, as the former can reduce mortality and xerophthalmia but often have minimal effects on concentrations of serum retinol (West, 2002). "
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    ABSTRACT: Variation in the relationship between plasma retinol-binding protein (RBP) and retinol (ROH) has implications for vitamin A (VA) status assessment using RBP. Our objectives were to identify factors affecting the RBP:ROH relationship and to derive and evaluate population-specific RBP cutoffs for VA deficiency (VAD) in Cameroon. Plasma RBP, C-reactive protein (CRP), α1-acid-glycoprotein (AGP), and ROH concentrations were compared in a subsample of women 15-49 y (n = 121) and children 12-59 mo (n = 123) included in a national survey conducted in 2009. Plasma RBP and ROH were highly correlated (r = 0.94 for women; r = 0.96 for children; P < 0.001). Pregnancy and lactation altered the RBP:ROH relationship in women, but obesity, elevated CRP and AGP, age, and VA status did not. Among children, age altered the RBP:ROH relationship, but sex, stunting, VA status, and elevated CRP and AGP did not. Cutoffs for VAD derived using regression analysis were <1.17 μmol RBP/L for women (corresponding to <1.05 μmol ROH/L) and <0.83 μmol RBP/L for children (corresponding to <0.70 μmol ROH/L). The sensitivity and specificity of derived cutoffs were 81.8 and 93.0% for women and 94.7 and 88.9% for children, respectively. The infection-adjusted prevalence of low VA status (<1.17 μmol RBP/L) was 21.9% (95% CI = 18.7-25.0%) among women. Among children, the infection-adjusted prevalence of VAD (<0.83 μmol RBP/L) was 35.0% (95% CI = 31.1-39.0%). In conclusion, VAD remains a public health problem in Cameroon. The RBP:ROH relationship should be considered in surveys using RBP to assess VA status, and use of population-specific cutoffs may be advisable.
    Journal of Nutrition 11/2011; 141(12):2233-41. DOI:10.3945/jn.111.145805 · 3.88 Impact Factor
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    ABSTRACT: In Cambodia, many factors may complicate the detection of iron deficiency. In a cross-sectional survey, we assessed the role of genetic hemoglobin (Hb) disorders, iron deficiency, vitamin A deficiency, infections, and other factors on Hb in young Cambodian children. Data on sociodemographic status, morbidity, and growth were collected from children (n = 3124) aged 6 to 59 mo selected from 3 rural provinces and Phnom Penh municipality. Blood samples were collected (n = 2695) for complete blood count, Hb type (by DNA analysis), ferritin, soluble transferrin receptor (sTfR), retinol-binding protein (RBP), C-reactive protein, and α(1)-acid glycoprotein (AGP). Genetic Hb disorders, anemia, and vitamin A deficiency were more common in rural than in urban provinces (P < 0.001): 60.0 vs. 40.0%, 58.2 vs. 32.7%, and 7.4 vs. 3.1%, respectively. Major determinants of Hb were age group, Hb type, ferritin, sTfR, RBP, AGP >1.0 g/L (P < 0.001), and rural setting (P < 0.05). Age group, Hb type, RBP, elevated AGP, and rural setting also influenced ferritin and sTfR (P < 0.02). Multiple factors affected anemia status, including the following: age groups 6-11.99 mo (OR: 6.1; 95% CI: 4.3, 8.7) and 12-23.99 mo (OR: 2.7; 95% CI: 2.1, 3.6); Hb type, notably Hb EE (OR: 18.5; 95% CI: 8.5, 40.4); low ferritin (OR: 3.2; 95% CI: 2.2, 4.7); elevated AGP (OR: 1.4; 95% CI: 1.2,1.7); rural setting (OR: 2.3; 95% CI: 1.7, 3.1); low RBP (OR: 3.6; 95% CI: 2.2, 5.9); and elevated sTfR (OR: 2.1; 95% CI: 1.7, 2.7). In Cambodia, where a high prevalence of genetic Hb disorders exists, ferritin and sTfR are of limited use for assessing the prevalence of iron deficiency. New low-cost methods for detecting genetic Hb disorders are urgently required.
    Journal of Nutrition 02/2012; 142(4):781-7. DOI:10.3945/jn.111.148189 · 3.88 Impact Factor
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