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Surrogate endpoints


Outcome measures that are not of direct practical importance but are believed to reflect outcomes that are important are called surrogate outcomes. For instance, cholesterol is used as a surrogate endpoint in many trials where cholesterol reduction is used as a surrogate for reduced mortality. The trouble is that trials to demonstrate mortality reduction have to be large, and long. Cholesterol reduction is known to be strongly associated with mortality benefits, and can be measured easily in smaller numbers of patients. In another example, blood pressure is not directly important to patients but it is often used as an outcome in clinical trials because it is a risk factor for stroke and heart attacks.

Surrogate endpoints are often physiological or biochemical markers that can be relatively quickly and easily measured, and that are taken as being predictive of important clinical outcomes. They are often used when observation of clinical outcomes requires long follow-up. The main thing to remember is that there has to be a good reason to accept a surrogate endpoint. We have to be sure that the utility of the surrogate is well established.