Intra-individual variation

Levels of ACHE and PCHE vary in healthy people because of genetic differences or under specific physio-pathological conditions inter-individual coefficients of variation of cholinesterase activity have been determined to be about 15 to 25% for PCHE and 10 to 18% for RBC-ACHE. Corresponding figures for intra-individual variations are 6% and 3 to 7%, respectively (Dillon and Ho, 1987). 

The glucose values are worthy of attention because of the large number of determinations that have been made in many laboratories. There is evidence of substantial intra-individual variation in glucose values which is in part responsible for the range of the observed values.33,34 In spite of this normal variance in values in the same individual, however, there is evidence that inter-individual differences exist among well people. Some, on repeated tests, tend to have low values, some intermediate, and some high. 

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. 

Concerted evolution apparently operates among neodermatan ribosomal operons (Collins and Cunningham, 2000). However, intraspecific and intra-individual variation is common in neodermatans and other eukaryotes, especially in spacers, and indicates that the force of concerted evolution cannot completely overcome contrary influences. Such influences include the effects of replication slippage and unequal crossing over, both of which can occur in regions of simple sequence, which is abundant in eukaryotic... 

Intra-individual variation in ITS1 is common and is often due to the presence of differing numbers of repeat regions. Other differences can be due to sequence variation, including insertions and deletions, outside the repeats. Differences between individuals can also have such a basis, and mention of this will be made in this section. 

Intra-individual variation in ITS1 is absent or slight in monogeneans (e.g. Zietara et al.,... 

Table 2 Intra-individual variations of clinical chemistry measurands in serum [1]...

Gibbs, A. and Crowe, J.H. (1991). Intra-individual variation in cuticular lipids studied using Fourier transform infrared spectroscopy../. Insect Physiol., 37, 743-748. 

P8. Popp-Snijders, C., Lips, P., and Netelenbos, J. C., Intra-individual variation in bone resorption markers in urine. Ann. Clin. Biochem. 33, 347-348 (1996). 

However, serum concentrations should be interpreted with caution in view of significant intra-individual variation (309). 

Most NSAIDs are well absorbed from the gastrointestinal tract, although there can be substantial inter- and intra-individual variations, e.g. indometacin [1, 24],... 

Kalow W, Tang BK, Endrenyi L. 1998. Hypothesis comparison of inter- and intra-individual variations can substitute for twin studies in drug research. Pharmacogenetics 8 283-89... 

Holzel WGE. Intra-individual variation of analytes in serum of patients witli chronic renal failure. Clin Chem 1987 33 670-3. 

Although the two-period crossover design has certain intrinsic weaknesses, intra-individual variation is usually smaller than variation between subjects, and bioequivalence can usually be established using a smaller number of subjects in a crossover study. The order in which subjects receive single doses of the different formulations must be randomised and an adequate interval allowed between doses to ensure washout. The number of subjects will depend on the variability of the kinetics of the compound. A power calculation should be performed using historical data, if possible. In practice, the minimum number of volunteers needed is 12 and the maximum usually about 24 but is occasionally more. The number and times of blood samples is a critical a sufficient number of samples is required around the to permit and to be identified with adequate accuracy. Sampling should continue for at least 3-4 half-lives and later samples should be spaced so that no more than about 15% (or ideally 10%) of the AUC has to be determined by extrapolation or interpolation between points. Model-fitted data are usually not acceptable should be obtained directly from the observed concentration data and... 

Mason HJ, Lewis PJ. Intra-individual variation in plasma and erythrocyte cholinesterase activities and the monitoring of uptake of organo-phosphate pesticides. J Soc Occup Med I4S4 39 121 4. 

Physiological factors that contribute to the intra-individual variation of blood constituents have been reviewed recently (Statland and Winkel, 1977, 1981 Young, 1979 Solberg and PetitClerc, 1988). Data on the effects of physiological changes on the concentrations of trace elements in blood are scanty, but it seems inevitable that physiological factors should also have similar effects on determination of their concentrations. 

Morrison, B., Shenkin, A., McLelland, A., Robertson, D.A., Barroman, M., Graham, S., Wuga, G. and Cunningham, J.K.M. (1979). Intra-individual variation on commonly analysed serum constituents. Clin. Chem., 25,1799. 

Brock, A. (1990). Immunoreactive plasma cholinesterase (EC 3.1.1.8) substance concentration compared with cholinesterase activity concentration and albumin Inter- and intra-individual variation in a healthy population group. J. Clin. Chent. Biochem. 28,851-856. 

Chambless LE, Roeback JR (1993) Methods for assessing difference between groups in change when initial measurements is subject to intra-individual variation. Statistics in Medicine 12 1213-1237. 

Ducey, P. K., Anthony, C. D., and Brodie, E. D., Jr., 1991, Thresholds and escalation of antipredator responses in the Chinese saiamander Cynops cyanurus inter- and intra- individual variation, Behav. Process. 23 181-191. 

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