Medical analysis laboratory must establish its own reference intervals depending on the facilities they are working with, the working substances and protocols. These reference intervals must be obtained depending on age groups in order to accurately interpret the results of the analyzes performed. The study is a retrospective one using 3217 data from the electronic archive of the SC Vladutiu & Garabedian SRL Clinic in Medias. Total serum calcium was determined by the colorimetric method on the Konelab analyzer. Processing of the collected data was done using the Hoffmann method, considering 5% up to 95% of the values in the database, the values being randomly selected. For comparison, data from the literature was used. In children under 1 year old, it was not possible to calculate the reference intervals since data was insufficient. In the other age groups, reference intervals obtained in the current study were similar to the studied literature. Reference intervals established for calcium can provide important guidance for the reasonable supplementation of this essential element in children.