From the Guidelines
ABI is the preferred initial diagnostic test for peripheral artery disease (PAD) due to its non-invasive nature and high specificity, whereas ABG is used to assess respiratory function and acid-base balance 1. When considering the diagnosis of PAD, the choice between ABI and ABG depends on the clinical presentation and suspicion of the disease.
- ABI is a non-invasive test that measures the ratio of blood pressure at the ankle to the blood pressure in the arm, with a normal range of 0.9-1.4 1.
- ABG, on the other hand, is an invasive blood test that analyzes arterial blood samples to assess respiratory function and acid-base balance, measuring parameters such as pH, PaO2, PaCO2, bicarbonate, and oxygen saturation 1. The American College of Cardiology/American Heart Association guidelines recommend using the resting ABI as the initial diagnostic test for PAD, with a sensitivity of 69% to 79% and a specificity of 83% to 99% compared to imaging studies 1. The resting ABI should be measured in each leg using a blood pressure cuff and a Doppler device, with the ABI calculated as the ratio of the higher systolic pressure in the ipsilateral dorsalis pedis and posterior tibial arteries divided by the higher of the left and right brachial artery systolic pressures 1. In patients with symptoms of PAD, an ABI < 0.9 is considered abnormal and suggestive of PAD, while an ABI > 1.4 may indicate noncompressible arteries, often seen in patients with diabetes or chronic kidney disease 1. In such cases, a toe-brachial index (TBI) can be used to evaluate for PAD, with a TBI of ≤ 0.70 considered abnormal 1. Overall, ABI is the preferred initial diagnostic test for PAD due to its non-invasive nature, high specificity, and ability to provide valuable information about the severity of the disease 1.
From the Research
ABI vs ABG: Understanding the Differences
- ABI (Ankle-Brachial Index) is a test used to diagnose Peripheral Artery Disease (PAD) by measuring the ratio of blood pressure in the ankles to that in the arms 2, 3, 4.
- ABG (Arterial Blood Gas) analysis, on the other hand, is a test used to assess the adequacy of ventilation, oxygenation, and acid-base status of the body by measuring the levels of pH, oxygen, carbon dioxide, and bicarbonate in arterial blood 5.
Clinical Relevance of ABI and ABG
- ABI is used to diagnose PAD, which is associated with cardiovascular disease and has a high prevalence in patients with chronic obstructive pulmonary disease (COPD) 2, 3.
- ABG analysis is used to diagnose and manage patients with pulmonary and critical conditions, and can play a major role in diagnosis and treatment of these patients 5.
- Patients with COPD and PAD have a higher prevalence of cardiovascular risk factors and more severe lung disease, highlighting the importance of diagnosing and managing PAD in these patients 2, 3.
Diagnostic Criteria and Methods
- ABI is calculated by dividing the systolic blood pressure in the ankles by the systolic blood pressure in the arms, and a value of ≤0.9 is indicative of PAD 2, 3, 4.
- ABG analysis involves measuring the levels of pH, oxygen, carbon dioxide, and bicarbonate in arterial blood, and can be used to diagnose a range of conditions, including respiratory and metabolic disorders 5.
- Ultrasound indices, such as peak systolic blood flow velocity (PSV) and blood flow acceleration velocity (AccV), can also be used to diagnose PAD and peripheral arteriosclerosis in patients with COPD 4.