Materials and Methods
From May to June 2009, a cross-sectional study was performed in school children, from grade 1 to grade 9, who were studying at a public school in Ongkhaluck province in Thailand. The majority of school children in Ongkahluck were from families with middle socio-economic status. All children who were scheduled to have blood examination as per the school policy for screening for ABO blood groups were eligible for the study. Children and their legal guardians were informed and approached for participation in the study. Children who already knew their blood group or refused to have their blood samples obtained were excluded from the study. The study protocol was approved by the Ethics Committee of the Faculty of Medicine, Srinakharinwirot University. Informed consent was obtained from children’s parents or guardians and assent was obtained from participating children.
Demographic data and anthropometric characteristics were collected by a trained member of our research group. Weight was measured to the nearest 100 grams using an electronic scale -Tanita Body Composition Analyzer (Model no. BF-680W, Tokyo, Japan). Height was measured to the nearest 0.1 cm. The Body Mass Index (BMI) was calculated as the ratio of weight/ (height) 2 [kg/m2]. Waist circumference was measured to the nearest 0.1 cm at the midpoint between the lower costal margin and the top of the iliac crest using a non-elastic flexible tape while the subject was in standing position [6]. Hip circumference was measured to the nearest 0.1 cm in standing position at the maximum circumference over the buttocks. Mid upper arm circumference was measured at the mid-point between olecranon process and the acromion process of the left arm. Triceps skinfold thickness was measured over the triceps muscle at the same level as mid arm circumference measurement using a lange skinfold caliper. Subscapular skinfold thickness was measured at the lower angle of the scapula of a relaxed left arm using the same caliper.