Selection Criteria and Evaluation of Subjects

The selection of reference individuals consists essentially of applying defined criteria to a group of examined candidate persons,The required characteristics of the reference values determine which criteria should be used in the selection process. Box 16-1 lists some important criteria to consider when the production of health-associated reference values is the aim. 

The question of which diseases and risk factors to consider for exclusion of individuals is difficult (see the discussion on the concept of health earlier in this chapter). The answer lies partly in the intended purpose of establishing reference values the project must be goal oriented. 

Similar problems affect the definition of hypertension in relation to the establishment of health-associated reference values and exclusion criteria based on laboratory examinations. It has been argued that we might be lost in a circular process when we use laboratory tests to assess the health of subjects who are subsequently to be used as healthy control subjects for laboratory tests. But actually there is no difference, in this context, between measuring the height, weight, and blood pressure and performing selected laboratory tests, provided that these laboratory tests are neither those for which we shall produce reference values nor tests that are significantly correlated with them.  

It is particularly difficult to define selection criteria when establishing reference values for a geriatric population. In higher age groups it is normal to have minor or major diseases and to take drugs. One solution is to collect values at one time and to use the values of survivors after a defined number of years.  

Usually the clinical evaluation of candidate individuals is based on an anamnestic interview or questionnaire, a physical examination, and supplementary investigations. Anamnestic and examination forms tailored to the requirements of the actual project facilitate the evaluation and document the decisions taken. 

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