Total amylase and pancreatic isoamylase in serum and urine: considerations from data on biological variation.

The analytical, within-subject and between-subject components of variation were estimated for amylase activity and pancreatic isoamylase activity in serum measured using newer analytical methods. Desirable analytical imprecisions based on within-subject variation were CV less than or equal to 4.4% and CV less than or equal to 7.0%, respectively. Conventional population-based reference intervals were not useful because of marked individuality; clinical decision-making points should be derived from the desired sensitivity and specificity. Serial results must change more than about 30% and 40% respectively before significance (P less than or equal to 0.05) can be claimed. Similar data on total amylase and pancreatic isoamylase activities in random and first morning urines showed that the use of conventional reference intervals was appropriate. Very large changes (greater than 100%) were required before a difference in serial results was significant. Calculation of the urine amylase/creatinine ratio appeared to confer no advantage. Derivation of the ratio of pancreatic isoamylase to total amylase activity in serum or urine was unlikely to provide additional information of value in either diagnosis or monitoring.

Biological variability of 26 clinical chemistry analytes in elderly people.

Analytical, within-subject, and between-subject components of variation were estimated for 26 clinical chemistry analytes from duplicate analyses of 10 specimens collected from 27 healthy elderly subjects over a period of 20 weeks. Within-subject variations were similar to those generated previously by us in younger subjects. We conclude, therefore, that homeostasis is not compromised by age alone, and biological variability does not increase simply with age. All analytes except serum water had marked individuality, showing that conventional population-based reference values are of limited utility. The critical differences required for two results to be significantly (P less than or equal to 0.05) changed are not the same as those that prompt action by clinicians. Although heterogeneity of within-subject variation does exist, we believe that the critical differences generated will be useful in routine clinical decision making.

Variability of capillary plasma glucose in healthy individuals in repeated 75 g oral glucose tolerance tests.

A series of ten 75 g oral glucose tolerance tests was carried out on each of 14 apparently healthy subjects. The analytical, intra-individual and interindividual components of variation were calculated by nested ANOVA following duplicate analyses of capillary plasma glucose under optimal conditions. The analyses met the objectively set analytical goal of CV less than or equal to 2.2%. There was considerable intra-individual variation, but no subject was ever classified as diabetic or having impaired glucose tolerance. Recent criteria for interpretation of results must be used since conventional population-based reference values are not adequate. Serial results from an individual must differ by more than 0.7 mmol/L for fasting specimens and at least 1.6 mmol/L for other specimens for a statistically significant (P less than or equal to 0.05) change to have occurred.

The impact of the child's deficiency on the father: a study of fathers of mentally retarded and of chronically ill children.

Psychological assessments of fathers of mentally retarded, of chronically ill, and of healthy children indicate that the first two groups undergo significant stress associated with their fathering a handicapped child. Some fathers of mentally retarded children appear subject to a pattern of neurotic-like constriction. Differences in the experiences of fathers and mothers of deficient children are discussed, and suggestions for treatment are offered.