Estimating reference ranges in clinical pathology: an objective approach

On the use of patient data for the definition of reference intervals in clinical chemistry

To improve the definition of reference intervals using patient data in clinical chemistry we studied the use of single results as a selection criterion (i.e. those results judged by the clinician not to require confirmation or which are considered unimportant for clinical screening purposes). Using this criterion 95% intervals were defined for S-albumin, S-cholesterol, S-creatinine, B-glucose, B-haemoglobin and S-urea similar to the corresponding reference intervals determined for healthy adults. Data collected from patients in the age interval 45-95 years demonstrated a significant decrease in levels of S-albumin and B-haemoglobin with age, an increase in S-creatinine, B-glucose and S-urea levels, and a biphasic variation in level of S-cholesterol. It is suggested that these changes are not caused by disease but result from the ageing process. The use of selected patient data for characterization of these changes enables a linear or polynomial description to be made for the age-related changes in the reference intervals.

Effect of body mass and other factors on serum liver enzyme levels in men attending for well population screening

Alcohol abuse is usually regarded as the most likely cause of elevated serum liver enzyme values in those attending for well population screening, but we have found increased body weight to be an important contributing factor. We have measured serum levels of alanine amino-transferase (ALT), aspartate aminotransferase (AST) and gamma-glutamyl transferase (GGT) in approximately 21,000 men attending for routine health screening, and related these to behavioural factors such as alcohol consumption, cigarette smoking, exercise level and obesity. The levels of all three enzymes were positively correlated with levels of alcohol consumption. Decreasing levels of physical activity were associated with increases in mean ALT and GGT levels. Cigarette smoking showed only a weak effect on ALT and AST, which became non-significant after multivariate statistical analysis, but increasing consumption of cigarettes was associated with increased mean levels of GGT. In contrast, all three enzymes showed marked increases in mean levels with increasing body mass index (BMI). The effect of obesity was particularly important in the case of ALT: the prevalence of increased ALT values in obese subjects (BMI greater than or equal to 31 kg/m2) was more than eight times that in those with normal weight (BMI less than or equal to 25 kg/m2), even after allowing for the confounding effect of alcohol consumption. This study is concerned solely with male subjects, but we hope to extend the analysis to females in the near future.