Wellcome lecture 1986. Ideas towards a general theory of clinical biochemistry

Clinical biochemistry, as an independent discipline within medical science, has developed its own body of theory and practice, and as such it cannot only be concerned with collecting observations. A simple report (plasma potassium = 5.3 mmol/L) is used as a model to discuss the problems of understanding measured chemical changes in the body in disease, and how these lead towards a general theory. These include the nature of the analysand and the reference base; accuracy and identification of the analyte; how disturbances of the steady state contribute to changes in a static result; the implications of precision; differences between activity, concentration and content; the convention of arithmetical concentration; and the meaning of 'abnormal', and of derived terms such as 'predictive value' and 'decision level'. Clinical biochemists/chemical pathologists, with their understanding of all these and related problems, must act as the necessary bridge between analysts and clinicians.