Intubation test A standard intubation test as described earlier14 will be performed in this subset of children after completion of iron absorption study. In brief, as soft gastric tube (18G) will be placed in most dependent part of stomach. Gastric acid samples will be collected from children lying in the left recumbent position using manual suction. The position of the tube will be confirmed by auscultation, aspiration of gastric juice, and nearly complete recovery of water injected in the tube. Samples of gastric juice will be discarded during the first 10 min after intubation. Thereafter, samples will be collected and saved in 15- min aliquot for 90 min. After 90 min of collection (basal sample), pentagastrin (peptavlon, ICI) will be injected subcutaneously at a dose of 0.6 ug/kg. The sample following pentagastrin stimulation for 60 min will be termed as "stimulated sample". The volime of gastric secretion in each of the 15 min collections will be rcorded and expressed as mililitre per hour. The concentrations of acid in each will be measured by titration of 1 mL gastric juice with 0.01N sodium hydroxide to pH 7.4, using an automated titrator (Metrohm, Herisau, Switzerland). Total acid output was calculated for each time pint by multiplying volume of gastric juice and acid concentration. Basal (BAO) and stimulated acid output (SAO) were calculated based on 2 samples collected for baseline measurement and the 4 samples collected after administration of pentagastrin respectively, and were expressed as mMol/h.