Using multiples of the median to normalize serum protein measurements

Quantification of serum proteins is useful in the diagnosis and clinical management of many disorders. With the introduction of automated analyzers and standardized reference materials, one of the last barriers to more widespread utilization of these measurements is the lack of availability of reliable and transferable age- and gender-specific reference ranges. One normalization method that deserves consideration is converting values to multiples of the median (MoM) for age and gender. When two analytic methods agree, or differ only by a proportional amount, conversion to MoM can be used to simplify the clinical interpretation of serum protein results. As a test of this method, assay results for IgG, transferrin, and albumin from three Swedish hospitals were normalized using published reference ranges from the United States. All assays were standardized to CRM 470. IgG results were in agreement in mass units, and transferrin measurements were proportionally different. However, there were important, non-proportional differences in albumin measurements. After converting IgG and transferrin measurements to MoM, published reference ranges were appropriate for the Swedish Hospitals.