Biological Variation and Hemoglobin A1c: Relevance to Diabetes Management and Complications

Biological variationThe term biological variation refers to differences in clinical attributes between individuals not due to measurement or analytic uncertainties (1).Pediatricians have frequent day-to-day experience with assessment and interpretation of biological variation; for example in healthy growing children height increases with age.But chronologic age is not the only determinant of height and at any given chronological age there is considerable variation in height between children.To facilitate relative height comparisons between children over time it is common practice to calculate a height z-score which removes the effect of age.Children tend to track in height and have consistency in height z-score over time, i.e., tall children tend to remain tall and short children short.The consistency of differences in height z-scores between individual children over time is an example of between-individual biological variation in height which is not due to differences of age.Between-individual biological variation is present in virtually all clinical measurements and can pose a particular challenge when interpreting results of blood samples sent to the clinical laboratory for analysis (1).When analytes are measured repeatedly from healthy individuals, the range of values from one individual often consistently occupies only a small part of the reference interval for the entire population (1, 2).Statistically, the variation in values for a repeatedly measured analyte between separate individuals in a population is greater than the variation of values for that analyte measured within individual members of the population.