Methodological aspects of the micronutrient assessment in the Brazilian National Survey on Child Nutrition (ENANI-2019): a population-based household survey

Abstract

This article aims to present methodological aspects on the collection, analyses, coverage, challenges, and the lessons learned from laboratory assessment of micronutrients on the Brazilian National Survey on Child Nutrition (ENANI-2019). This is a household survey on a probability sample of children under five years of age from 123 Brazilian municipalities in all 26 states and the Federal District. Blood samples were drawn by venipuncture at the homes of children 6 to 59 months of age. This procedure was performed by experienced phlebotomists from the laboratories located in the selected municipalities and scheduled in advance. Blood and serum levels were measured for biomarkers of nutritional status, using the services of a clinical test laboratory with nationwide coverage, for the following micronutrients: iron (hemoglobin and ferritin), zinc, selenium, folic acid, and vitamins A, B1, B6, B12, D, and E. C-reactive protein was analyzed as a marker of inflammation. A barcode identifier was used to track the blood samples and to link the biochemical test results to the other data collected in the survey. A total of 14,558 children were studied. Of the 12,598 eligible children, 8,829 (70.1%) had blood samples drawn. Of the total number of children who had samples drawn, 91.8% (n = 8,025) have results for at least nine of the 12 analyses performed. Coverage of the analysis varied from 95% (for vitamins A and E) to 84.2% (for folic acid). Aliquots of whole blood and serum were stored in a biorepository for future analyses. The results of this pioneering study in the country will back the formulation and, when necessary, the reorientation of public policies in food and nutrition.

Sampling plan of the Brazilian National Survey on Child Nutrition (ENANI-2019): a population-based household survey

“…Laboratory analyses of blood samples showed unit non-response (lack of measures for all the biomarkers) and item non-response (lack of measures for some subset of biomarkers), as observed in Castro et al 5 . Considering the nature of these measurements, we decided that it was not possible to compensate for non-response in this set of variables using imputation.…”

“…Data were collected after the child's parents or guardians signed two copies of the free and informed consent form. The methods used in the development of ENANI-2019 have been described in detail in specific publications 2,3,4,5 .…”

Prevalence and predictors of vitamin D insufficiency in Brazilian children under 5 years of age: Brazilian National Survey on Child Nutrition (ENANI-2019)

“…A sample size of 3000 households per Brazilian geographical region was defined, considering a minimum proportion of 2 %, a relative error estimate of 35 %, a confidence level of 95 % and a sampling and design effect set at 2. Details of the sample design, study completion and reasons for not drawing blood samples have been published previously (11)(12)(13) .…”

Methodological aspects of the assessment of dietary intake in the Brazilian National Survey on Child Nutrition (ENANI-2019): a population-based household survey

“…Data were collected after obtaining the signature of two copies of the informed consent form of the child's parent or guardian, who received one of the signed copies. The methods employed in the overall development of ENANI-2019 and those used in domains II and III are described in detail elsewhere in specific publications 11,12,13,14 .…”

“…Errores de recogida o incompletitudes en el sistema eran corregidos inmediatamente, y el equipo de campo era sistemáticamente contactado e informado sobre su desempeño, siendo reiteradas las orientaciones de recogida de datos. Todos los niños de la muestra fueron evaluados usando los dos instrumentos, obteniéndose datos referentes al cuestionario estructurado de cada uno de los 14…”