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.