Surreal image of a leg with artery-roads and a question mark-shaped blood pressure cuff, symbolizing ABI test accuracy concerns.

Peripheral Artery Disease: Are You Getting Accurate Ankle Brachial Index Results?

Rhea Morgan in Health & Wellness November 2025 • 4 min read.

"New research reveals how factors like diabetes and smoking can skew ABI readings, leading to potential misdiagnoses."

The ankle brachial index (ABI) is a common, non-invasive test used to diagnose peripheral artery disease (PAD). PAD affects millions worldwide, particularly older adults. The ABI test measures the blood pressure in your ankles and compares it to the blood pressure in your arms. This comparison helps doctors determine if there is any blockage in the arteries of your legs.

While the ABI test is generally reliable, recent studies have uncovered that the results can vary depending on individual patient characteristics. This variability, known as the 'spectrum effect' and 'spectrum bias,' means that certain factors, such as diabetes, smoking, and age, can influence the accuracy of the ABI test. This can lead to both false positive and false negative results, potentially affecting treatment decisions.

Understanding these nuances is crucial for anyone at risk of PAD, as well as for healthcare providers who use the ABI test. By being aware of the factors that can skew results, patients and doctors can work together to ensure more accurate diagnoses and appropriate care.

Understanding the Spectrum Effect and Spectrum Bias in ABI Testing

Surreal image of a leg with artery-roads and a question mark-shaped blood pressure cuff, symbolizing ABI test accuracy concerns.

The 'spectrum effect' refers to the way the ABI test's sensitivity and specificity (its ability to correctly identify those with and without PAD) changes across different patient groups. For example, an ABI test might be very accurate in one group of people but less so in another. The 'spectrum bias' takes this a step further. It means that these variations can significantly alter the post-test probabilities, leading to misinterpretations of the results.

A study published in Atherosclerosis in March 2018 investigated how these effects influence the ABI test. The researchers compared oscillometric ABI (a common method) with Doppler ABI (a more detailed technique) in two different settings: primary care and vascular service centers. They analyzed 374 legs from 197 patients, considering factors like diabetes, smoking status, hypertension, and age.

Sensitivity and Specificity Variations: The study found that sensitivity (the ability to correctly identify PAD) ranged from 61.5% to 90.9% depending on the subgroup. Specificity (the ability to correctly identify those without PAD) varied from 81.8% to 99.1%.
Factors Influencing Results: Logistic regression analysis confirmed that factors such as the setting (primary care vs. vascular service), diabetes, smoking status, and age significantly impacted the ABI test results.
Impact on Positive and Negative Results: Positive ABI tests were less reliable in patients with diabetes, smokers, and those over 75 years old, leading to a higher rate of false positives. Negative ABI tests were less reliable in primary care patients, non-diabetics, and smokers, potentially leading to false negatives.

These findings highlight the importance of considering individual patient characteristics when interpreting ABI test results. A blanket approach to diagnosis can lead to errors, emphasizing the need for a more personalized assessment.

What This Means for You

If you're at risk for PAD, it's essential to discuss these findings with your doctor. Ask how your individual factors might influence the accuracy of an ABI test. This might involve additional testing or a more comprehensive evaluation of your vascular health. Remember, accurate diagnosis is the first step toward effective management and prevention of PAD-related complications. Keep the conversation open, and work with your healthcare team to ensure you're receiving the best possible care.

About this Article -

This article was crafted using a human-AI hybrid and collaborative approach. AI assisted our team with initial drafting, research insights, identifying key questions, and image generation. Our human editors guided topic selection, defined the angle, structured the content, ensured factual accuracy and relevance, refined the tone, and conducted thorough editing to deliver helpful, high-quality information.See our About page for more information.

This article is based on research published under:

DOI-LINK: 10.1016/j.atherosclerosis.2018.03.003, Alternate LINK

Title: Spectrum Effect And Spectrum Bias In The Oscillometric Ankle Brachial Index To Diagnose Peripheral Arterial Disease: Clinical Implications

Subject: Cardiology and Cardiovascular Medicine

Journal: Atherosclerosis

Publisher: Elsevier BV

Authors: Ángel Herráiz-Adillo, Iván Cavero-Redondo, Celia Álvarez-Bueno, Johana Bidner, Vicente Martínez-Vizcaíno, Blanca Notario-Pacheco

Published: 2018-05-01

Everything You Need To Know

What is the ankle brachial index (ABI) test?

The ankle brachial index (ABI) is a non-invasive test used to diagnose peripheral artery disease (PAD). It compares the blood pressure in your ankles to the blood pressure in your arms. A lower ABI reading suggests a blockage in the leg arteries, which is indicative of PAD. This test is a critical initial step because PAD is a common condition, particularly among older adults. The ABI helps doctors determine if further investigation or treatment is needed to prevent complications.

What are the 'spectrum effect' and 'spectrum bias' in the context of ABI testing?

The 'spectrum effect' describes how the accuracy of the ankle brachial index (ABI) test, specifically its sensitivity and specificity, varies across different patient groups. Sensitivity refers to the test's ability to correctly identify PAD, while specificity refers to its ability to correctly identify the absence of PAD. The 'spectrum bias' builds on this, showing that these variations can lead to misinterpretations of the results. This is significant because it can result in both false positive and false negative readings of the ABI, potentially affecting diagnosis and treatment decisions.

How can factors like diabetes and smoking influence the results of the ABI test?

Factors like diabetes and smoking can significantly impact the ankle brachial index (ABI) test results. Studies have shown that these factors can skew the accuracy of the test. For example, in individuals with diabetes, the ABI test may be less reliable, potentially leading to inaccurate diagnoses. Similarly, smoking can affect the ABI readings, leading to similar issues. The implications are that healthcare providers must consider these factors when interpreting ABI results to avoid misdiagnoses and ensure appropriate care. Considering these factors is critical for accurate PAD diagnosis.

What does it mean if my ABI test results are affected by certain factors?

If your ankle brachial index (ABI) test results are affected by factors like diabetes, smoking, or age, it means the test might not be as accurate. This could lead to a misdiagnosis of peripheral artery disease (PAD). For instance, you could receive a false positive (diagnosed with PAD when you don't have it) or a false negative (not diagnosed with PAD when you do have it). These inaccuracies can impact treatment decisions, potentially leading to unnecessary treatments or a delay in receiving the care you need. Discuss these potential influences with your doctor to get a more personalized evaluation.

How should I address the potential influence of my individual risk factors on the ABI test?

You should discuss how your individual risk factors might influence the accuracy of an ankle brachial index (ABI) test with your healthcare provider. This is crucial because the ABI test's reliability can be affected by factors like diabetes, smoking, age, and the setting where the test is performed. Discussing these influences helps ensure you receive an accurate diagnosis and appropriate care for peripheral artery disease (PAD). Depending on your individual risk factors, your doctor might recommend additional tests or a more comprehensive evaluation of your vascular health to confirm the ABI findings.