Do I need to test both extremities for an Ankle-Brachial Index (ABI) test?

Ankle-Brachial Index Testing Requires Measurement of Both Extremities

Yes, you need to test both extremities when performing an Ankle-Brachial Index (ABI) test. The ABI should be measured in both legs in all new patients with peripheral artery disease (PAD) of any severity to confirm the diagnosis and establish a baseline 1.

Why Both Extremities Must Be Tested

1. Diagnostic Accuracy:

   • PAD may be unilateral or more severe in one leg than another
   • Using the lower ABI of the two legs will identify more individuals at risk of cardiovascular events 1
   • When only the higher ABI is used, individuals with significant disease who are at high risk of cardiovascular events may be missed 1

2. Establishing Baseline:

   • Bilateral measurements provide a complete baseline for future comparison
   • Allows detection of disease progression over time

3. Clinical Guidelines Support:

   • The American College of Cardiology Foundation/American Heart Association (ACCF/AHA) guidelines explicitly state: "The ABI should be measured in both legs in all new patients with PAD of any severity to confirm the diagnosis of lower extremity PAD and establish a baseline" (Level of Evidence: B) 1

Proper ABI Measurement Protocol

The American Heart Association recommends the following sequence for ABI measurement 1:

1. First arm systolic pressure
2. First posterior tibial (PT) artery
3. First dorsalis pedis (DP) artery
4. Other PT artery
5. Other DP artery
6. Other arm systolic pressure

If the systolic blood pressure of the first arm exceeds the second arm by >10 mm Hg, the blood pressure of the first arm should be repeated and the first measurement disregarded 1.

Calculation and Interpretation

• Calculation: The ABI for each leg is calculated by dividing the higher of the PT or DP pressure in that leg by the higher of the two brachial pressures 1

• Interpretation of Results 1:

  • Noncompressible: >1.40
  • Normal: 1.00-1.40
  • Borderline: 0.91-0.99
  • Abnormal (PAD): ≤0.90

Clinical Implications

Testing both extremities has significant implications for:

1. Mortality and Morbidity Assessment:

   • An abnormal ABI (≤0.90) in either leg indicates increased risk of cardiovascular events and mortality 1
   • Individuals with an ABI <0.90 or >1.40 should be considered at increased risk of cardiovascular events and mortality independently of symptoms 1

2. Treatment Planning:

   • Bilateral testing helps identify the need for targeted interventions
   • Allows for appropriate follow-up and monitoring of disease progression

Common Pitfalls to Avoid

1. Testing only one leg: This can miss unilateral disease or asymmetric disease severity
2. Using only one ankle artery: Guidelines recommend using the higher of the PT or DP pressure for each ankle 1
3. Failing to repeat arm measurements when there's >10 mm Hg difference between arms
4. Incorrect interpretation of borderline values: Values between 0.91-0.99 should be considered borderline and may warrant further evaluation 1

By testing both extremities, you ensure comprehensive assessment of PAD risk and establish a complete baseline for future comparison, which is essential for optimal patient care and cardiovascular risk assessment.