Many studies are carried out on "healthy volunteers". But what exactly does this term mean? And why are healthy volunteers needed?

In spite of the lightning speed of progress of research, we are still far from perfectly understanding the anatomy and physiology of the normal human being. Not only is research on healthy volunteers worthwhile for the advancement of Science, but it also serves as a basis for the study of disease.

On the other hand, certain clinical trials and tests of medical devices are easier to conduct on healthy volunteers, at least in the first phases (phase 1 for the drug trials). The difficulty in this case is knowing to what extent the results obtained on healthy volunteers can be extrapolated to the population with the condition for which the treatment is intended.

If researchers were limited to using 100% healthy volunteers, with no history of disease, no anatomical variations, no pathology (not even a cavity!), none would ever be found! It is necessary, then, to understand the term "healthy volunteer" as regards the context of the study. Even though a person who suffers from skin allergies could be considered healthy for a neurophysiologic test, that would not be the case for the test of a cosmetic product.

Consequently, the process of including healthy volunteers generally includes a medical examination. While it could be a matter of a simple questionnaire for a medical imaging test, it could involve a blood draw, an electrocardiogram and possibly other exams for the drug trials. The purpose of these medical workups is to verify that the volunteer meets the criteria for inclusion in the study and that he does not suffer from any illness he is not aware of.

It is not always easy for the researchers to draw the line between healthy volunteers and volunteers from the patient population. "Normality" is variable from one subject to another and even within a single individual. Compare your blood levels from two blood samples drawn 15 days apart: most will be slightly different, but both are considered "normal". Compare them with a friend in good health: they will be different, but both will also be normal. It is to take into account this intra- and inter-subject variability that it is important to perform a recruitment medical visit that is specially-designed for each study, and to recruit a sufficiently large number of volunteers so that the sample is as representative as possible of the population.

Other factors can also be taken into account in the recruitment of healthy subjects. For example, it must be determined whether or not the subjects regularly take medications that could interfere with the results of the study. Weight and the consumption of tobacco and alcohol are also generally part of the criteria. Before offering to participate in a study, read the details of the offer carefully. If anything is unclear to you, do not hesitate to ask questions and discuss it with the researcher.

References:

• Brazzell RK, Colburn WA. Controversy I: Patients or healthy volunteers for pharmacokinetic studies? J Clin Pharmacol 1986;26:242-247.
• Sibille M et al. Laboratory data in healthy volunteers: reference values, reference changes, screening and laboratory adverse event limits in Phase I clinical trials. Eur J Clin Pharmacol 1999;55:13-19.