The Necessity for Additional Information

The clinical situation often is different from a controlled research situation specimens have to be taken during operations, in emergency situations, or when patients are unwilling or unable to follow instructions. Therefore the clinician needs additional information for the interpretation of a patient s values in relation to reference values obtained under fairly standardized conditions. 

An empirical approach is to produce other sets of reference values, such as postprandial values, postexercise values, 

There is another and more general solution to the problem, called the predictive approach Starting from a set of ordinary reference values and using quantitative information on the effect of various factors, such as intake of food, alcohol, and drugs exercise stress or posture, we could estimate expected reference values that fit the actual clinical setting (see Chapter 17).  

More studies of such effects are needed, especially for the combined effect of two or more sources of variation. Is, for example, the combined effect of alcohol and contraceptive drugs on y-glutamyltransferase activity in serum less than, equal to, or greater than the sum of their individual effects  

Essential components of the required definition of a set of reference values are specifications concerning (1) the analy- 

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