Individual character of variation in time-series studies of healthy people: II. Differences in values for clinical chemical analytes in serum among demographic groups, by age and sex.

Abstract

Assessment of the significance of an observed set of serum chemical values for determining a person's state of health requires comparison with a set of defined reference values. We tested the assumption that a reference group of individuals, categorized by age and sex, gives a narrower range of variation than does a larger mixed population. If this were true, the demographic set would be a more sensitive reference than is the customary "normal range" for interpretation of values occurring in the individual. The ratio, R, of intra-personal to inter-personal (group) standard deviations was similar for defined age/sex classes and the overall group for 16 serum constituents. When the "raw" intra-individual variation (biological plus analytical variation) was adjusted to remove the average analytical component, the resulting R was less than 80 for all constituents except creatine kinase, which indicates that these are all particularly strong "discriminators" of individuality. These results imply the need for individual rather than population-based reference ranges, even if the latter are from persons of similar age and the same sex.

ARIC Hemostasis Study - III. Ouality Control

“…In comparing laboratory QC studies one must also take care in noting definitions of parameters and different methods of estimation. In some cases o3 (t: , 14) is assessed using control plasma, likely thereby understating true processing and measurement variation. In some cases ( 15) , there is no inter-run variation because all runs were saved and done in the same batch, again understating total variation.…”

Individuality and responsiveness of biochemical indices of dehydration in hospitalized elderly patients

“…A low I] means high individuality. If I, is <0.6, the PBRR will be almost always insensitive to statistically significant changes from an individual's own mean value [27]. As I r increases above 0.6, the probability that such a deviation will fall outside the PBRR increases until for I[> 1.4; this probability is very high (/>>0.95) [27].…”

“…If I, is <0.6, the PBRR will be almost always insensitive to statistically significant changes from an individual's own mean value [27]. As I r increases above 0.6, the probability that such a deviation will fall outside the PBRR increases until for I[> 1.4; this probability is very high (/>>0.95) [27]. These criteria are based on the assumption that an individual's serial test results will show a normal distribution.…”

Patient-specific analysis of sequential haematological data by multiple linear regression and mixture distribution modelling

“…For example, for a sequence of length 5 and a desired signiÿcance level of 0•05; the estimated risk for the one-change model selected by the leaps and bounds method was multiplied by 3•68. 1 Similarly, the estimated risk for the two-change model selected by the leaps and bounds method was multiplied by 3•68 2 . The weighted risk estimates were then compared to the estimated risk for the null (no-change) model and the 'optimal' model was chosen as the one with the smallest weighted estimated risk.…”

“…There is considerable evidence, however, that for many blood constituents, the average amount of within-person variation over time (excluding measurement error) is much less than the between-person variation. [1][2][3] Thus, when analytic variation is reduced, the magnitude of variation in haematologic parameters measured in healthy individuals over time will be small in comparison to the reference ranges in use. An observation that is within the population-based reference range may represent a clinically signiÿcant deviation from one subject's usual condition, whereas another result, outside population-based limits, may just represent expected random variation for another subject.…”