USPSTF Final Recommendations
Insufficient Evidence on CVD-related Screening, Risk Assessment
July 11, 2018, 11:48 am News Staff – On July 10, the U.S. Preventive Services Task Force (USPSTF) released two final recommendation statements and evidence summaries related to screening for cardiovascular disease (CVD): a final recommendation statement and final evidence summary on screening for peripheral artery disease (PAD) and CVD risk assessment using the ankle-brachial index (ABI), and a final recommendation statement and final evidence summary on risk assessment for CVD using nontraditional risk factors.
In each case, USPSTF members concluded that the available evidence was insufficient to assess the balance of benefits and harms of the practice examined.
These final recommendations are consistent with the task force's 2018 draft recommendations.
ABI Screening for PAD, CVD Risk Assessment
Resting ABI is the most commonly used test for detection of PAD in clinical settings, although results can vary based on the precise measurement protocol used. Calculated as the systolic blood pressure obtained at the ankle divided by that obtained at the brachial artery in a patient who is lying down, a ratio of less than 1 (typically defined as <0.9) is considered abnormal and is commonly used to define PAD.
According to the USPSTF, however, although a low ABI value is frequently used as a surrogate marker for PAD in practice, its accuracy as a screening tool for PAD in asymptomatic primary care patient populations has not been well studied.
The task force examined current evidence to see whether screening asymptomatic patients with ABI helped reduce mortality or morbidity from CVD or PAD. Based on its review, the USPSTF found insufficient evidence to assess the balance of benefits and harms of screening for PAD and CVD using the ABI in adults -- an "I" statement.
"We know that the ABI can be used for diagnosis of PAD in people with symptoms," said USPSTF member Seth Landefeld, M.D., in a news release. "However, the task force looked at whether it can be used to identify the risk of developing blocked vessels in the leg among people without signs or symptoms of PAD. At this time, there is not enough evidence to recommend for or against using the ABI as a screening tool."
In addition to its January draft recommendation statement, this final recommendation statement updates and is consistent with the task force's 2013 final recommendation statement. The AAFP agreed with the USPSTF's 2013 recommendation at that time.
A draft version of this final recommendation statement was posted for public comment on the USPSTF website from Jan. 16 to Feb. 12.
Story Highlights
Several commenters said they were concerned that the task force didn't release a separate positive recommendation for patients at higher risk for developing PAD, including older adults; patients with diabetes, hypertension or high cholesterol levels; and those who currently use tobacco.
"The USPSTF found the evidence addressing screening for PAD in high-risk, asymptomatic populations to be limited, with no compelling evidence to support differential screening or treatment in subpopulations at greater risk," the final recommendation said.
Additionally, the task force said patients in higher-risk groups would likely already be candidates for interventions based on their global CVD risk, which raises concern about the clinical significance of screening for additional risk factors such as asymptomatic PAD.
To clarify this point, the USPSTF added language to the statement's Accuracy of Screening Tests and Effectiveness of Early Detection and Treatment areas in the Discussion section.
Commenters also said an I statement could negatively affect health care disparities for PAD, citing evidence that PAD has a disproportionately higher prevalence among racial/ethnic minorities and low-socioeconomic populations. These commenters also said the I statement could discourage testing and perpetuate disparities in treatment and outcomes.
"The USPSTF recognizes these well-established disparities in care," the final recommendation said. "However, the evidence on screening and treatment in these groups is currently lacking, and the USPSTF was unable to determine the overall balance of benefits and harms."
Finally, the USPSTF added language to the Research Needs and Gaps area in the Other Considerations section calling for future research on this topic to include diverse populations.
CVD Risk Assessment With Nontraditional Risk Factors
The second USPSTF final recommendation statement looked at whether adding certain nontraditional risk factors to traditional CVD risk models could improve risk assessment for CVD in asymptomatic adults.
Traditional CVD risk assessment tools used to inform treatment to prevent CVD events through risk factor modification, such as the Framingham Risk Score, the Pooled Cohort Equations or similar models, are based on age, race/ethnicity, gender, diabetes, smoking status, cholesterol levels and blood pressure.
The task force examined evidence regarding use of three nontraditional CVD risk factors -- the ABI, high-sensitivity C-reactive protein (hsCRP) and coronary artery calcification (CAC) score -- ultimately concluding that the evidence was insufficient to assess the balance of benefits and harms of adding these three factors to traditional risk assessment for CVD in asymptomatic adults to prevent CVD events -- an "I" statement.
"While there is some evidence that the ABI, CAC and hsCRP can provide clinicians with additional information on risk, we could not determine whether this was enough to help clinicians make better treatment or care decisions," said USPSTF member Michael Barry, M.D., in the release. "More research is needed to know if adding these three tests for nontraditional risk factors to CVD risk assessment can help improve our ability to prevent heart attack or stroke."
In addition to its January draft recommendation statement, this final recommendation statement updates and is consistent with the USPSTF's 2009 final recommendation statement. At the time, the AAFP mirrored this guidance in its own recommendation.
The USPSTF listed the primary potential harm of adding nontraditional risk factors to CVD risk assessment as low-dose radiation exposure from CAC score measurement. More general potential harms are false-positive test results and subsequent invasive diagnostic procedures, such as coronary angiography.
A draft version of this final recommendation statement was posted for public comment on the USPSTF website from Jan. 16 to Feb. 12.
Many commenters said evidence for risk assessment with CAC score was strong enough to warrant a separate positive recommendation.
"Although adding CAC score to traditional risk assessment models improved discrimination and reclassification, the USPSTF found inadequate evidence that this change would translate into improved health outcomes among asymptomatic patients," the final recommendation said.
Several other commenters said they were concerned the task force overestimated the harms associated with CAC score testing (radiation exposure, downstream testing).
"The USPSTF added language to clarify that it determined that the harms associated with the addition of nontraditional risk factors, including CAC score, are small in magnitude," the final recommendation said.
Additional commenters said adding nontraditional risk factors -- especially CAC score -- was useful for patients whose risk stratification was unclear or for those who fall into intermediate-risk groups.
The USPSTF responded by saying it hadn't found convincing evidence that adding nontraditional risk factors to traditional risk factors improves reclassification in intermediate-risk groups.
"As clinical practice moves toward a single threshold for treatment, this concern may no longer be relevant in clinical decision-making," the task force said.
Some commenters said CAC score testing leads to better adherence to preventive therapies (i.e. medications and lifestyle changes).
The USPSTF responded by adding language to its final recommendation statement addressing this point by saying it had carefully reviewed the available evidence and concluded that CAC score testing showed no benefit over traditional CVD risk assessment in preventive medication use or risk factor control.
Several commenters recommended including more information on the differences between the Framingham Risk Score and the Pooled Cohort Equations as well as population distribution of risk, which the task force added to the Clinical Considerations section.
Finally, commenters said the USPSTF's assessment might not be applicable across sex, race/ethnicity, family history and socioeconomic status. So, the task force added language indicating the need for more studies in these subpopulations.
Up Next
The AAFP plans to review the USPSTF's final recommendation statements and supporting evidence, and then release its own recommendations on the topics.
Related AAFP News Coverage
USPSTF Draft Recommendations
Evidence Lacking on CVD-related Screening, Risk Assessment
(1/22/2018)