Abstract
Abstract Objectives Plasma glucose concentrations exhibit a pronounced daytime-dependent variation. The oscillations responsible for this are currently not considered in the determination of reference limits (RL) and decision limits. Methods We characterized the daily variation inherent in large-scale laboratory data from two different university hospitals (site 1 n=513,682, site 2 n=204,001). Continuous and distinct RL for daytime and night were estimated. Diurnal characteristics of glucose concentrations were further investigated by quantile regression analyses introducing age and cosinor-functions as predictors in the model. Results Diurnal variations expressed as amplitude/Midline Estimating Statistic of Rhythm (MESOR) ratio, averaged 7.7% (range 5.9–9.3%). The amplitude of glucose levels decreased with increasing concentrations. Between 06:00 and 10:00 h an average decrease of 4% has to be considered. Nocturnal glucose samples accounted for only 5% of the total amount but contributed to 19.5% of all findings over 11.1 mmol/L. Partitioning of RL between day and night is merely justified for the upper reference limit. The nocturnal upper RLs for both genders differed from those obtained during the day by 11.0 and 10.6% at site 1 and by 7.6 and 7.5% at site 2. Conclusions We conclude that indirect approaches to estimate upper RL of random plasma glucose concentrations require stratification concerning the time of sample collection.
Highlights
The biological variation in plasma glucose levels results from the complex interaction of genetically anchored metabolic processes that are subject to strict hormonecontrolled regulation
We conclude that indirect approaches to estimate upper reference limits (RL) of random plasma glucose concentrations require stratification concerning the time of sample collection
Estimation of RL based on the truncated maximum likelihood (TML) approach [7, 8] employing the Reference Limit Estimator (RLE) software developed by the Working Group on Guide Limits of the German Society of Clinical Chemistry and Laboratory Medicine (DGKL)
Summary
The biological variation in plasma glucose levels results from the complex interaction of genetically anchored metabolic processes that are subject to strict hormonecontrolled regulation. Clinical decision limits exist for all the respective prandial states. In addition to this extrinsic factor, there are intrinsic regulatory mechanisms that have developed evolutionarily and determine a centrally anchored diurnal rhythm of glucose metabolism independent of food intake [6]. These intrinsic mechanisms contribute to a certain extent systematically and predictably to the biological variability of glucose levels in a population
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