Intra- and Interindividual Variations

In general, the variations due to analytical components in clinical chemistry measurements usually are much less than variations due to the preanalytical factors. The 

A similar formula can be used when the corresponding coefficients of variations are substituted to obtain a measure of imprecision. The probability that the difference between test values from the same animal is significant at the 95% level (i.e., this difference occurs by chance at fewer than 1 in 20 occasions) can be expressed by the formula 2.8 x SD ab and is known as a critical difference. The critical difference may also be calculated by the formula  

96 X the square root of 2 x (biological coefficient of variation for intraindividual + analytical coefficient of variation ) 

In some reported canine studies, 1.96 is replaced by 2 (Fraser 2001,2004 Martinez-Subiela, Tecles, and Ceron 2003 Jensen and Aaes 1992). 

Some measurements of the biological variation that occur for both intra- and interindividual animals have been made in rat studies (Lindena, Btittner, and Trautschold 1984 Carakostas and Banerjee 1990) and dog studies (Leissing, Izzo, and Sargent 

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Le Beau MA, Christenson RH, Levine B, Darwin WD, Huestis MA. Intra- and interindividual variations in urinary concentrations of endogenous ganrnia-hydroxybutyrate. J Anal Toxicol 2002 26 340-6. 

Intra- and interindividual variations in protease inhibitor drug exposure can influence the safety and effectiveness of anti-HIV therapy. In the example presented here, in addition to the description of the pharmacokinetics of nelfinavir and its metabolite, it was possible to evaluate the impact of the coadministration of ritonavir. 

LeBeau M.A., Darwin W.D. and Huestis M.A. (2000b). Intra- and interindividual variations in urinary levels of endogenous GHB. In Proceedings - Society of Forensic Toxicologists Annual Meeting, Milwaukee, WI, p. 5. 

Intra- and Interindividual Variations, Critical Differences, and Reference Ranges... 

Beckman O, Bondesson E, Asking L, Kallen A, Borgstrom L. Intra- and interindividual variations in pulmonary deposition via Turbuhaler and pMDI. Drug Delivery to the Lungs VI. The Aerosol Society, 1995. 

Table 1 Biological setting points for electrolyte total ion concentrations and active molalities. Estimations of cVb% are based on physiological ranges given by the intra- and interindividual variation referred to the mean biological setting point...

Flanagan JM, Popendikyte V, Pozdniakovaite N et al. Intra- and interindividual epigenetic variation in human germ cells. Am J Hum Genet 2006 79 67-84. 

Any analysis of biomonitoring data should include an assessment of the importance of sources of variation. Basic sources to be considered are laboratory, intra-individual, interindividual, and variability attributable to groups. 

In experiments carried on in the author s laboratory several years ago, the B vitamin content of milks from individual cows and from individual human mothers was determined.63 So far as this study is concerned, involving as it did only B vitamins, the intra-individual variation (that is, from day to day) appeared to be greater than interindividual differences. The number of human cases studied was not sufficient to be the basis of any sound conclusion on this point. 

V(inter) is the interindividual or between subject variance and V(intra) is the intraindividual or within person variance which includes both true day-to-day variation and any random methodological error. 

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