Current Insights On ABI And Diagnosing PAD
However, some more recent studies have called this into question. Niazi and colleagues recently reported that high ankle pressure ABI had a sensitivity of 69 percent and specificity of 83 percent.9 Khan and coworkers critically reviewed ABI methods and found low ankle pressure ABI generally has better sensitivity in diagnosing PAD.8 However, high ankle pressure ABI is the current method endorsed by the American College of Cardiology Foundation (ACCF) and the American Heart Association (AHA).10
The ankle brachial index has become the gold standard office-based test to screen for peripheral vascular disease but this test is still underutilized.11 Why is ABI testing often overlooked in primary care settings or podiatry offices?
Perhaps some practitioners believe they should only perform the ABI when patient has a non-healing wound or intermittent claudication. This belief may be further reinforced by the large percentage of tests that come back with normal results. However, it may come as a surprise to some to learn that the majority of patients with PAD are asymptomatic.12 This is an important point to emphasize because screening asymptomatic patients for PAD represents a significant paradigm shift in the way practitioners typically think about diagnosing PAD.
A recent study by Daddato and colleagues calls attention to the excellent opportunity for podiatrists to screen asymptomatic patients with ABI testing.13 The study focused on 749 adults who received PAD screening after presenting to an Italian podiatry clinic. All patients were asymptomatic for PAD and free from cardiovascular diseases. The patients also completed a simple questionnaire for cardiovascular risk factors. Among the entire study population, 8.3 percent of males and 1.2 percent of females had diagnosed PAD. Among those diagnosed with PAD, hypercholesterolemia and hypertension were the highest risk factors reported in 76 percent and 52 percent of patients respectively. The findings of this study were in line with previous studies conducted in other countries but are especially relevant because they were limited to asymptomatic podiatry patients.
A Closer Look At The 2011 ACCF/AHA Recommendations For ABI Screening
When should a podiatrist offer ABI testing to his or her patients? There is no right answer for every podiatry practice. However, the American College of Cardiology Foundation and American Heart Association recently updated their 2005 guidelines for ABI screening and suggest a uniform way of reporting outcomes.14 These 2011 ACCF/AHA guidelines should work well for most podiatry practices.
1. The resting ABI should establish the lower extremity PAD diagnosis in patients with suspected lower extremity PAD, defined as individuals with one or more of the following:
a. Exertional leg symptoms
b. Non-healing wounds
c. Age 65 years or older
d. Age 50 years and older with a history of smoking or diabetes
2. One should measure the ABI in both legs in all new patients with PAD of any severity to confirm the diagnosis of lower extremity PAD and establish a baseline.
3. The ABI results should be uniformly reported in the following categories:
a. Non-compressible >1.40
b. Normal 1.00 to 1.40
c. Borderline 0.91 to 0.99
The 2011 ACCF/AHA guidelines differ significantly from the 2005 guidelines. First, the threshold of 70 years or older decreased to 65 years. Second, the way we report ABI results has been updated with uniform categories. The categories are not complicated and are easy to remember. Additionally, the 2011 guidelines are supported by higher-level evidence than the 2005 guidelines, including data derived from randomized trials.10,14
The ACCF/AHA guidelines are straightforward and evidence-based. They will help eliminate confusion on which patients to offer ABI testing. This consideration is very important in a group practice setting where multiple podiatrists and perhaps physicians of differing specialties need to agree on the standard of care.