A prospective cohort study is conducted to assess the relationship between elevated C-reactive protein level (exposure) and the development of acute coronary syndrome (disease). A sample of 100 adults age 45 is categorized according to their C-reactive protein (CRP) levels. After a 5-year follow-up period, the following data were obtained: What is the 5-year risk of getting acute coronary syndrome in subjects with elevated CRP levels?

Question

A prospective cohort study is conducted to assess the relationship between elevated C-reactive protein level (exposure) and the development of acute coronary syndrome (disease).  A sample of 100 adults age >45 is categorized according to their C-reactive protein (CRP) levels.  After a 5-year follow-up period, the following data were obtained:  What is the 5-year risk of getting acute coronary syndrome in subjects with elevated CRP levels?

Quizplus · Accepted Answer

Risk is the statistical likelihood of experiencing an adverse event. In epidemiology, risk is a measure of incidence of a disease of interest; that is, the probability of developing the disease over a certain period of time (eg, 5 years). To calculate the risk of a disease of interest (eg, acute coronary syndrome [ACS]) in subjects with an exposure of interest (eg, elevated C-reactive protein [CRP] level), divide: number of subjects with the exposure who develop the disease (eg, number of subjects with elevated CRP level who develop ACS = 10) by total number of subjects with the exposure (ie, exposed/at risk) (eg, total number of subjects with elevated CRP level = 20) In this example, 10/20 = 0.5, which is interpreted as a 50% probability of developing ACS in 5 years. Note that the data are not presented in the standard 2 x 2 format (with exposure status in the rows, and disease status in the columns), requiring appropriate interpretation of the values in each cell. (Choice B) The 5-year risk of developing ACS in all study subjects is 30/100 = 0.3 (30%). (Choice C) The 5-year risk of developing ACS in subjects without elevated CRP levels is 20/80 = 0.25 (25%). (Choice D) The prevalence of exposure (ie, elevated CRP levels) in the entire cohort (all subjects, regardless of exposure/disease status) is 20/100 = 0.2 (20%). (Choice E) The prevalence of exposure in nondiseased people is 10/70 = ~0.14 (~14%). Educational objective: Risk is the probability of developing a disease over a certain period of time. To calculate the risk, divide the number of exposed subjects with the disease by the total number of exposed subjects (ie, all subjects at risk).

A Prospective Cohort Study Is Conducted to Assess the Relationship