[Reference values in biology. Use and special value in preventive medicine].

The idea of reference values should replace in biology, the idea of normal or abnormal values. In fact, progress in physiopathology and laboratory techniques has demonstrated the difficulty of fine interpretation of laboratory examinations. It is first necessary to understand factors of variation due to sampling, then the techniques of analysis themselves. Then, the importance of variations within and between individuals for each laboratory examination. Among the most important factors, we may quote age, sex, drugs, exercise, etc. These various possibilities of interference may be classified in order to remember only those which may falsify reference values, i.e. the values used for clinical interpretation. Thus, these factors are of greater importance in preventive medicine where finer and earlier variations may be observed. The best reference is that of the individual himself, if laboratory examinations are to be used profitably both in preventive and curative medicine. It would be necessary to draw up, for each subject, reference values during a period of good health between the ages of 18 and 25.