LAUSR

Åsberg [1] and co-authors analyzed a NHANES dataset to show that RCVs calculated as fixed percentages lead to inconsistent interpretations, and that RCV calculations with functions lead to more consistent interpretations. I read this study with interest. The NHANES dataset did not include the time of day when pairs of samples were collected so direct assessment of the influence of diurnal variation on RCVs was not possible. Patient pairs of NHANES test results that are inherently affected by diurnal variation will demonstrate greater differences in observed values and in this manner, diurnal variations contribute to the slope values observed and reported by Åsberg [1] and co-authors as functions. The extent of the contribution of diurnal variation to the slopes could not be determined. I agree with the authors’ conclusion that use of RCVs calculated as fixed percentages are not ideal for consistent clinical interpretation. I hope that future studies will extend the work by Åsberg [1] and co-authors that RCVs should be calculated and interpreted with knowledge of both functions and test diurnal variation to reliably detect clinically significant changes in test results. To assess this hypothesis future studies will require data sets with detailed information about the time of day that specimens were collected.