Background: Calcium exists in human blood in a free form and in a form bound to plasma proteins, principally albumin. Since it is the ionized form that is biologically active, it has long been common practice to present calcium adjusted on the basis of serum albumin concentration. The concept of adjusted calcium has only been evaluated in adults. In this study, we evaluated the use of the adult-adjusted equation to report calcium in children.
Methods: We searched the laboratory information system over three teaching hospitals for young patients aged between newborn and 18 years old with a request for calcium and albumin analysis but with no evidence of disturbances of calcium homeostasis. These data were organized on the basis of age and was separated into four age groups (birth to 1 month old, 1 month to 1 year old, 1 to 5 years old and 5 to 18 years old). These data were subjected to regression analysis to derive the calcium-adjusted equation for each age group.
Results: There is an inverse relationship between the bias value and the age. The younger the age, the higher the difference between the adjusted calcium calculated by the adult equation and that calculated by the age-specific equation. This pattern was maintained on all sites.
Conclusion: For all sites, the adult-adjusted calcium equation may be used to calculate the adjusted calcium for children aged one year old and above.