Interpretation of laboratory results also includes the comparison of the result with a predetermined reference range. The reference ranges represent the areas in which 95 percent of the value of the samples of healthy individuals is located. The reference range of the analyte may differ from laboratory to laboratory due to differences in population, method, apparatus, etc. Establishing one's own reference range would be desirable in terms of accuracy, but impracticable due to its scale. As an alternative solution, the laboratory is offered the so called verification of reference ranges. After reviewing the literature, the laboratory decides on a reference range that has been established in the local population or where the same methods have been used, and tries to prove its suitability for the given conditions.
Our task was to verify the reference ranges used in the Laboratory for the Diagnosis of Hormones and Tumor Markers for the analytes 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D. These are metabolites of vitamin D; 25-hydroxyvitamin D represents a supply in the body, and 1,25-dihydroxyvitamin D is a steroid hormone and represents the active form.
Verification was performed by selecting a reference population and measuring serum analyte concentrations. We then collected a homogeneous sample of 20 values with normal distribution using statistical tests and compared them with the reference ranges. The reference range for 25-hydroxyvitamin D was successfully verified despite seasonal fluctuations. We were unable to verify the reference range for 1,25-dihydroxyvitamin D used in the laboratory. However, the values coincided with the range specified by the manufacturer. It is proposed to replace the reference values for 1,25-dihydroxy vitamin D for those established by the manufacturer.
Despite the successful verification of the range for 25-hydroxy vitamin D, the question arises as to its significance or usefulness. The fact is that the majority of the population in Slovenia is malnourished with vitamin D and consequently the reference values do not represent optimal values for health. In case the reference range does not serve as a tool for clinical decisions, a sensible substitution for the recommended values could be considered.
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