Health services are organized by levels of care, which improves outcomes. These levels are "filters" that lead to a progressive increase in the prevalence of diseases in higher levels of care. We studied and justified the role of the general practitioner as filter, or gatekeeper, to specialists and hospitals. This role leads to greater prevalence of diseases in the referral population. We analyzed empirical data on abdominal pain, chest pain and rectal bleeding as examples. As to rectal bleeding, the prevalence of rectum and sigma carcinomas increases from 0.1% in the population, to 2% in general practitioners' waiting rooms (as a consequence of personal and family filters), and to 36% in specialists' waiting rooms (as a consequence of the gate-keeping role general practitioners play). This increase in prevalence improves the positive predictive value of the specialist's diagnostic testing, and patient selection avoids unnecessary contacts of specialists with patients having benign causes of rectal bleeding (who remain at their appropriate family or general practitioners' level).
Gatekeeping; Primary Care; General Practitioner/Family physician