Abstract
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.