Investigations
1st investigations to order
ankle-brachial index (ABI)
Test
Sensitivity of 95% and specificity of 100%. May not be accurate in patients with non-compressible arteries, such as those with comorbid diabetes mellitus or chronic kidney disease (CKD), particularly those on dialysis. Patients with either severely stenotic or totally occluded arteries may also have normal ABI if there is abundant collateral system present.[45] Diagnosis of peripheral arterial disease should not be excluded based on normal or raised ankle-brachial pressure index alone in people with diabetes or CKD.[2][46]
Result
ABI ≤0.90
Investigations to consider
toe-brachial index (TBI)
Test
The TBI should be used to establish the diagnosis of peripheral arterial disease (PAD) in patients in whom lower extremity PAD is clinically suspected, but in whom the ankle-brachial index (ABI) test is not reliable due to non-compressible vessels, such as in those with comorbid diabetes or chronic kidney disease, or those with advanced age.[2]
TBI should be measured to diagnose patients with suspected PAD when the ABI is >1.40.[2]
Result
TBI <0.6
segmental pressure examination
Test
Arterial pressure can be measured with plethysmographic cuffs sequentially placed along the limb at various levels.[2] Unlike the ankle-brachial index, the segmental pressure analysis is able to determine the location and magnitude of stenosis. It is also cheap and quick.
Result
gradient of >20 mmHg between adjacent segments
pulse volume recording
Test
Now used less because of the emergence of duplex ultrasound. Evaluates the arterial pressure waveform via the use of a pneumoplethysmographic device. Accurate in patients with non-compressible arteries; however, its measurements are qualitative, not quantitative.[2]
Diagnostic accuracy is in the range of 90% to 95%. May not be accurate in diagnosing stenosis of the distal segments.
Abnormal in patients with low cardiac stroke volume.
Result
any qualitative sequential decrease in pulsatility of the waveform
duplex ultrasound
Test
Peak systolic velocity ratio >2.0 = stenosis >50%.
Is the most widely used modality to assess location and degree of stenosis as well as patency of bypass grafts.[48] The sensitivity and specificity of ≥50% stenosis from the iliac artery to popliteal artery are 90% and 95%.
Result
peak systolic velocity ratio >2.0
continuous wave Doppler ultrasound
Test
Provides an accurate location and severity of peripheral arterial disease.[2] Limited accuracy in tortuous, calcified, and overlapping vessel and lower sensitivity for iliac artery disease. Also, in patients with superficial femoral artery stenosis, there is lowered specificity.
Pulsatility index might be normal distal to the stenosis, which can also diminish test sensitivity.
Result
pulsatility index decrease between adjacent proximal and distal anatomical segments
exercise ankle-brachial index (ABI)
Test
The magnitude of the walking limitations can be assessed and it is a good measure of therapeutic benefit.[2] Useful in establishing the diagnosis of lower extremity peripheral arterial disease in symptomatic patients when resting ABIs are normal or borderline.[2] Typically, a motorised treadmill is used and patients are exercised on Naughton, Hiatt, or Gardner-Skinner protocol.
Result
post-exercise ABI < pre-exercise ABI
catheter angiography
Test
Digital subtraction technique provides superior resolution because it eliminates bony and dense body tissue artefacts. However, it is an invasive procedure requiring contrast.
Result
anatomical detail of stenoses or occlusions
CT angiogram
Test
Requires intravenous contrast, although there is less radiation than with traditional angiography.[2] It can also reconstruct the images into 3D images. The new 64-slice CT can have sensitivity from 89% to 100% and specificity from 92% to 100% for >50% stenosis.
However, its spatial resolution is lower than digital subtraction angiography and venous opacification can obscure arterial filling.
Result
anatomical detail of stenoses or occlusions
magnetic resonance angiography (MRA)
Test
MRA is useful to diagnose anatomical location and stenosis.[2] Sensitivity and specificity of MRA in a meta-analysis to detect a stenosis >50% was 90% to 100%, with the greatest accuracy when gadolinium was used. However, it does have several limitations. MRA tends to overestimate stenosis and occlusions. Metal clips can mimic occlusions, thus limiting its use in post-surgical patients. Also, patients with pacemakers, defibrillators, and some cerebral aneurysm clips cannot be scanned safely.
Gadolinium has caused nephrogenic systemic fibrosis in patients with chronic renal insufficiency.
Result
anatomical detail of stenoses or occlusions
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