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There are lots of factors that confer increased risk of diseases, and the knowledge about these risk factors are pivotal on diagnosis and prevention of pathologies. For example, smoking is a habit that confers increased risk to cardiovascular diseases and cancer. This information was obtained by epidemiological research and can help doctors to correlate the presence of this habit and probability of disease. What is more, this relation indicates that public health actions are necessary to decrease the prevalence of the factor, and consequently, disease. These actions reduce costs of health and may increase health expectancy.
The importance of research about risk factors goes beyond the medical area, because people are always worried about extending their life, and avoiding risk factors they can reach it. This fact makes research about these factors extremely important. A significant matter is that risk factors can be of any source, such as DNA, environment, radiation, chemicals and any other. For example, an increased risk of cancer is presented by persons exposed to: genetic abnormalities ( p53 and etc. ) and radiation. Drugs, bacteria, virus, lifestyle and chemical products are also important is the development of diseases. All these factors must be present before the beginning of disease, and their proper risk is dependent on dose, frequency, intensity of exposure, exposure period. This fact is extremely important on the definition of real risk, because the intrinsic properties of a risk factor can differ persons with high risk from low-risk ones. With this information we can recognize the risk conferred by a certain factor, and avoid the final incident, the disease.
Although, recognizing risk factors is not so simple, due to the possibility of interactions among some other factors. For example, patients with myocardial infarction ( MI ) are commonly exposed to risk factors, such as tobacco, alcohol, positive family history, hypertension, blood lipid abnormality, diabetes mellitus, obesity and some others. This variety of factors can act together in order to increase the risk of MI by multiplying their effects, and they can also play an important role in disease and primary prevention. The risk factors are used in order to predict happens, to obtain a cause-effect relation, to diagnosis ( discussed in a previous paper ) and prevention. This text discusses the uses of risk, its measurement and interpretation.
Risk factors confer an increased risk of disease to a person, and this can help practitioners to predict the natural history of disease, and when possible, change it by primary prevention. Although, this information of “elevation of risk” must be interpreted cautiously, because sometimes medical articles describe a risk as 20, 30 times greater in risk population than in normal population ( without risk factor ), but the incidence of disease is extremely little in both.
The risk factors can cause a disease, but they can be presented as markers of disease. Markers are as important as causal factors, because all the properties described in this text are maintained.
Comparison of risks
Risk is closely related to incidence, so that comparing incidences from the control and disease groups can indicate if a factor leaded to an increased risk of developing a disease, if is neutral or even a protective factor. Furthermore, there are some useful kinds of risk, each one based on incidences, that are able to give additional information and consist on an easy way to consider and communicate data about risks. One of the most used forms to express risk is the risk attributable to certain factor, that means how many diseases are consequence of this factor. It is expressed by a formula ( AR = exposed group Incidence - control group Incidence).
Another form is relative risk, that compares the same incidences in a division ( RR = exposed group Incidence / control group Incidence ). An example of the use of this assessment was recently published by Schulman et al. In this trial, 227 patients were followed during 4 years after their second episode of venous thromboembolism, in order to find out whether a six month treatment or an indefinite treatment with anticoagulant are effective and safe. Among 111 patients in the 6 months group there were 23 recurrences of thromboembolism, while in the indefinite group, 116 patients had only 3 cases of recurrence. As the proposed treatment was indefinite, this is used as control, and we have: RR = 8, it means that patients using this therapy are 8 times less likely to have a recurrence. This group had also less deaths and no excess of major hemorrhage. The interpretation of relative risk should be well understood. The control group is considered to have a risk equal to 1, and in relation to this group the other can be <1 ( protective factor ) or >1 ( risk factor ). This result must be taken cautiously, and if the confidence interval crosses 1 ( control ), it should be not taken as a real result.
The previous example and explanation showed clearly how to interpret a risk, yet there are another ways to express risk, as for example attributable risk in population ( ARP ) that is simply AR plus prevalence of exposure and expresses what portion of the incidence of a disease is due to certain risk factors. Finally, population attributable fraction ( PAF ) is calculated by dividing ARP by the total incidence of a disease, and represents the part of a disease that is caused by a risk factor.
In conclusion, we should know some important characteristics of risk development and presentation to guide our patients to a healthy life, with no risks. This task is impossible but we can use some epidemiological information to know which factors lead to a high risk of diseases and instruct others about it, so that using relative risk, attributable risk and other ways to measure risk is of great interest of practitioners to avoid future problems and maintain healthy before treating diseases.
1. Fletcher RH, Fletcher SW, Wagner EH. Clinical epidemiology: the essentials. Williams & Wilkins, 1996.
2. Schulman S, Granqvist S, Holmström M et al. The duration of oral anticoagulant therapy after a second episode of venous thromboembolism. NEJM 1997; 336:393-8.
3. Morganstern H, Kleinbaum DG, Kupper LL. Measures of disease incidence used in epidemiologic research. Int J Epidemiol 1980; 9:97-104.
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