Researchers are studying the relationship between essential hypertension and a common mutation in the structure of a sodium channel protein. A study population is randomly selected and blood samples are obtained for leukocyte genotyping. The prevalence of hypertension is determined based on mean blood pressure measurements obtained using standardized ambulatory blood pressure monitoring conducted over 1 week. Based on the analysis results, the researchers conclude that the sodium channel structure mutation is associated with hypertension. Which of the following best describes the study design used by the investigators?

Question

Researchers are studying the relationship between essential hypertension and a common mutation in the structure of a sodium channel protein.  A study population is randomly selected and blood samples are obtained for leukocyte genotyping.  The prevalence of hypertension is determined based on mean blood pressure measurements obtained using standardized ambulatory blood pressure monitoring conducted over 1 week.  Based on the analysis results, the researchers conclude that the sodium channel structure mutation is associated with hypertension.  Which of the following best describes the study design used by the investigators?

Quizplus · Accepted Answer

11ec160b_372d_c382_9249_ddf7848c27b1_MD0001_00 A cross-sectional study (also known as a prevalence study) simultaneously measures exposures and outcomes. The cross-sectional study has a "snapshot" design that is frequently used in surveys, mostly because it is inexpensive and easy to perform. In this example, a snapshot was obtained of individuals randomly selected from the population; their blood samples were analyzed for the presence of the sodium channel protein mutation and the prevalence of hypertension was calculated. The subjects' blood pressure was measured over 7 days to obtain an average measurement (likely to limit the results being impacted by white-coat hypertension and other transient causes of hypertension). The major limitation of a cross-sectional study design is that a temporal relationship between exposure and outcome is not always clear. However, in this case, demonstrating a temporal relationship was straightforward because the possession of a specific genotype clearly precedes hypertension. (Choice A) A case-control study is designed by selecting individuals with a particular disease (cases), individuals without that disease (controls), and then evaluating previous exposure status. This study would have been classified as a case-control study if it had explicitly recruited individuals with (cases) and without (controls) hypertension (rather than randomly selecting a sample from a population) and evaluated their sodium channel mutation patterns. (Choices C and E) A prospective cohort study would have taken individuals without hypertension from the population, analyzed their blood samples to determine the distribution of the sodium channel mutation, and followed them over time (years) to determine the proportion of new cases of hypertension in patients with and without the mutation. In this example, although hypertension was measured over several days, the objective was not to document incidence of new cases of hypertension (which would be unlikely to develop over 1 week) but to measure the prevalence of hypertension while ensuring that average blood pressure measurements were obtained. A retrospective design would have also assessed incidence (not prevalence) of hypertension compared to an earlier period of time, based on a chart review of historic data. Prospective and retrospective cohort studies are organized by selecting a group of individuals (ie, a cohort) who do not have the disease of interest (eg, hypertension), determining their exposure status, and then following them (forward in time or from a point in the past to the present) to assess for the development of the disease. (Choice D) A randomized clinical trial directly compares >2 treatments. Usually, the subjects are randomly assigned to experience a specific exposure (eg, a medication) or no exposure (eg, placebo) and are then followed to assess for the outcome of interest (eg, disease). Educational objective: In a cross-sectional study, exposure and outcome are measured simultaneously at a particular point in time ("snapshot study"). In other study designs, a certain time period separates the exposure from the outcome.

Researchers Are Studying the Relationship Between Essential Hypertension and a Common