Proxy Markers of Serum Retinol Concentration, Used Alone and in Combination, to Assess Population Vitamin A Status in Kenyan Children
Elise F. Talsma *
Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands.
Hans Verhoef
Cell Biology and Immunology Group, Wageningen University, Wageningen, The Netherlands and London School of Hygiene and Tropical Medicine, MRC International Nutrition Group, London, UK.
Inge D. Brouwer
Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands.
Anne Mburu-deWagt
Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands.
Paul J. M. Hulshof
Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands.
Alida Melse-Boonstra
Division of Human Nutrition, Wageningen University, Wageningen, The Netherlands.
*Author to whom correspondence should be addressed.
Abstract
Objectives: To assess the diagnostic performance of serum concentrations of retinol-binding protein (RBP), transthyretin, retinol concentration measured by fluorometry and RBP:transthyretin molar ratio, either alone or in combination, to estimate the prevalence of vitamin A deficiency (serum retinol concentration <0.70 μmol/L measured by high-performance liquid chromatography(HPLC)).
Methods: A cross-sectional study was conducted in 15 primary schools in Kibwezi and Makindu districts in Eastern province, Kenya in June 2010 with 375 schoolchildren (6-12 years), 25 randomly selected from each school by lot quality assurance sampling.
Results: Complete data were collected for 372 children. Mean serum concentration of retinol (HPLC), RBP and transthyretin were 0.87 (SD 0.19) µmol/L, 0.67 (SD 0.17) µmol/L and 3.0 (SD 0.62) µmol/L. The mean RBP: Transthyretin molar ratio was 0.23. The prevalence of vitamin A deficiency measured with HPLC was 18%. Transthyretin and RBP showed the largest area under the curve (AUCs 0.96 and 0.93, respectively). Logistic regression resulted in a model predicting vitamin A deficiency based on RBP, transthyretin and C-reactive protein (AUC: 0.98) and prevalence depending cutpoints for the linear predictor were calculated.
Conclusions: Combination of transthyretin, RBP and C-reactive protein in a linear predictor showed excellent diagnostic performance in assessing vitamin A status, and has great potential to eventually replace serum retinol concentration measured by HPLC as the preferred method to assess the population burden of vitamin A deficiency. Further research is needed to confirm whether this linear predictor yields similar results in different populations and laboratories. Our methodology can be widely applied for other diagnostic aims.