Situation: A 70-year-old man who has smoked for 50 years comes to the Rural Health Unit (RHU) because of calf pain when walking. He has type 2 diabetes and hypertension. The physician measures his ankle–brachial index (ABI). Which ABI value is the upper cut-off for diagnosing peripheral artery disease (the disease is diagnosed at this value or lower)?

The ankle–brachial index is the ankle systolic pressure divided by the brachial systolic pressure. A value of 0.90 or lower indicates peripheral artery disease, 0.91 to 0.99 is borderline, 1.00 to 1.40 is normal, and a value above 1.40 suggests calcified, noncompressible arteries.

The ankle–brachial index (ABI) is calculated by dividing the systolic blood pressure measured at the ankle by the systolic blood pressure measured at the brachial artery. It is a simple, noninvasive bedside tool used to screen for and diagnose peripheral artery disease (PAD), particularly in patients with risk factors such as long-term smoking, type 2 diabetes, and hypertension.

For this patient, the upper cut-off value for diagnosing PAD is 0.90. In other words, an ABI of 0.90 or lower indicates the presence of peripheral artery disease. Values from 0.91 to 0.99 are considered borderline, while 1.00 to 1.40 is the normal range. An ABI above 1.40 suggests calcified, noncompressible arteries, which can produce falsely elevated results.

The ABI reflects the ratio of lower-extremity perfusion pressure to systemic pressure; a reduced ratio means that arterial narrowing or occlusion is limiting blood flow to the leg. In a patient with classic symptoms of intermittent claudication—calf pain that occurs with walking and resolves with rest—an ABI at or below 0.90 confirms the clinical suspicion of PAD.

Key point! The question asks for the upper cut-off, meaning the highest value at which PAD is still diagnosed. That value is 0.90, not 1.00 or 1.40.

The ABI is widely recognized as a sensitive and cost-effective screening tool for PAD, and it is particularly valuable in high-risk populations such as smokers, older adults, and patients with diabetes or hypertension ^[3]. However, its diagnostic accuracy can be limited in certain subgroups. In people with diabetes, arterial calcification and vessel stiffness may make the ankle arteries noncompressible, leading to falsely normal or elevated ABI values despite significant atherosclerotic disease ^[1][2]. This is why an ABI above 1.40 is not interpreted as normal but rather as a sign of calcified vessels that may require alternative testing.

For diabetic patients with suspected PAD and an unreliable ABI, the toe–brachial index (TBI) may be more useful because the digital arteries are less susceptible to medial calcification and vessel stiffness . The TBI can detect early atherosclerotic changes that the ABI might miss in this population.

The diagnostic thresholds for ABI are summarized below.

ABI Value	Interpretation
0.90 or lower	Peripheral artery disease (PAD)
0.91–0.99	Borderline
1.00–1.40	Normal
Above 1.40	Calcified, noncompressible arteries

Watch out! Do not confuse the upper cut-off for PAD diagnosis with the lower limit of the normal range. The normal range begins at 1.00, but PAD is already diagnosed at 0.90 or below. The gap of 0.91–0.99 represents a borderline zone that warrants further evaluation.

In clinical practice, when a patient presents with exertional calf pain and has multiple cardiovascular risk factors, obtaining an ABI is a priority nursing and diagnostic step. A value of 0.90 or lower not only confirms PAD but also identifies the patient as being at increased risk for cardiovascular events, regardless of whether symptoms are present. The ABI therefore serves both diagnostic and prognostic purposes ^[3].

For this 70-year-old man with a 50-year smoking history, type 2 diabetes, and hypertension, the finding of calf pain with walking strongly suggests arterial insufficiency. The correct upper cut-off for diagnosing PAD is 0.90.