Applied Evidence

Aspirin for primary prevention: USPSTF recommendations for CVD and colorectal cancer

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Risk based on dose and formulation

The effect of aspirin dose and formulation on bleeding risk is uncertain. Some studies have shown an increased risk for bleeding with daily doses of aspirin ≥ 300 mg, while others have shown no significant increase in rates for bleeding with differing doses.21,25 Enteric coating does appear to lower the rates of gastric mucosal injury, although there are few data on the effect toward reducing clinically significant bleeding.26 Currently, several prospective studies are underway to help clarify the evidence.27

Putting it all together

For the general population, the evidence shows that the benefits and harms of aspirin for primary prevention are relatively even. The USPSTF guidelines are the first to recommend aspirin for both CVD and cancer prevention while taking into account the bleeding risk. According to the findings of the USPSTF, the balance of benefits and harms of aspirin use is contingent on 4 factors: age, baseline CVD risk, risk for bleeding, and preferences about taking aspirin.6 The complete recommendations from the USPSTF, along with other leading organizations, are outlined in TABLE 2.6,28-31

Summary of guideline recommendations on use of low-dose aspirin for primary prevention

Applying the evidence and varying guidelines in practice can feel daunting. Some practical tools have been developed to help clinicians understand patients’ bleeding risk and potential benefits with aspirin use. One such tool is highlighted below. Others are also available, and each has its own strengths and weaknesses.

Aspirin-Guide ( is a Web-based clinical decision support tool with an associated mobile application. It uses internal calculators (including the pooled cohort calculator prepared jointly by the American College of Cardiology and the American Heart Association) to assess CVD risk as well as bleeding risk. This tool gives clinicians patient-specific numbers-needed-to-treat and numbers-needed-to-harm when considering starting aspirin for primary prevention. It gives specific recommendations for aspirin use based on the data entered, and it also gives providers information to help guide shared decision-making with patients.32 Unfortunately, this decision support tool and others do not take into account the data from the most recent trials, so they should be used with caution.

LCDR Dustin K. Smith, DO, Naval Branch Clinic Diego Garcia, PSC 466, Box 301, FPO, AP 96595;

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