The Meaning of Secondary Prevention

A November letter to the editor in American Family Physician chastises that publication for misusing the term “secondary prevention,” even using it in the title of an article that was actually about tertiary prevention.

I am guilty of the same sin. I had been influenced by simplistic explanations that distinguished only two kinds of prevention: primary and secondary. I thought primary prevention was for those who didn’t yet have a disease, and secondary prevention was for those who already had the disease, to prevent recurrence or exacerbation. For example, vaccinations would be primary prevention and treatment of risk factors to prevent a second myocardial infarct would be secondary prevention.

No, there are three kinds of prevention: primary, secondary and tertiary. Primary prevention aims to prevent disease from developing in the first place. Secondary prevention aims to detect and treat disease that has not yet become symptomatic. Tertiary prevention is directed at those who already have symptomatic disease, in an attempt to prevent further deterioration, recurrent symptoms and subsequent events.

Some have suggested a 4th kind, quaternary prevention, to describe “… the set of health activities that mitigate or avoid the consequences of unnecessary or excessive interventions in the health system.” Another version is “Action taken to identify patient at risk of overmedicalisation, to protect him from new medical invasion, and to suggest to him interventions, which are ethically acceptable.” But this is not a generally accepted category.

Stedman’s medical dictionary defines secondary prevention as “interruption of any disease process before the emergence of recognized signs or diagnostic findings of the disorder.”

The Encyclopedia Britannica defines it as “early detection of disease or its precursors before symptoms appear, with the aim of preventing or curing it.”

A CME website explains the definitions used by the USPSTF:

The U.S. Preventative Services Task Forces’ Guide to Clinical Preventive Services (2d edition, 1996) describes secondary prevention measures as those that “identify and treat asymptomatic persons who have already developed risk factors or preclinical disease but in whom the condition is not clinically apparent.” (pp xli)  These activities are focused on early case finding of asymptomatic disease that occurs commonly and has significant risk for negative outcome without treatment. Screening tests are examples of secondary prevention activities, as these are done on those without clinical presentation of disease that has a significant latency period such as hyperlipidemia, hypertension, breast and prostate cancer.  With early case finding, the natural history of disease, or how the course of an illness unfolds over time without treatment, can often be altered to maximize well-being and minimize suffering.

Tertiary prevention activities involve the care of established disease, with attempts made to restore to highest function, minimize the negative effects of disease, and prevent disease-related complications.

The Library Index says “Secondary prevention, also called ‘screening,’ refers to measures that detect disease before it is symptomatic.”

The Encyclopedia of Public Health says:

Secondary prevention generally consists of the identification and interdiction of diseases that are present in the body, but that have not progressed to the point of causing signs, symptoms, and dys-function. These preclinical conditions are most often detected by disease screening (and follow-up of the findings). Examples of screening procedures that lead to the prevention of disease emergence include the Pap smear for detecting early cervical cancer, routine mammography for early breast cancer, sigmoidoscopy for detecting colon cancer, periodic determination of blood pressure and blood cholesterol levels, and screening for high blood-lead levels in persons with high occupational or other environmental exposures.

But usage is inconsistent and confusing. In addition to American Family Physician, several other organizations and publications such as the National Library of Medicine, the British Medical Journal, and the American Heart Association use the term “secondary prevention” to include patients who already have symptomatic disease.

Is this just unimportant nit-picky quibbling by self-appointed language police? I don’t think so. Science requires precise terminology and agreement about definitions. The letter to the editor in AFP gives an example of a situation where imprecision could lead to patients being harmed.  Beta blockers reduce morbidity and mortality in patients after MI, but they have been shown to increase morbidity in patients with hypertension who have not already had an MI.  If a writer recommends them for “secondary prevention” thinking he is talking about patients who have had an MI, a reader might misunderstand and give them to patients who have not yet had one.

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