Indications

Symptomatic patients: to diagnose PAD

• For individuals with leg symptoms or signs that are suggestive of PAD, guidelines recommend ankle brachial index (ABI) and ankle pressure (AP) and as the first-line screening tests to diagnose PAD.[2][4][5] 
  
• Signs and symptoms of PAD include [1] (See section 'Background' in topic "Arterial Ulcers - Introduction and Assessment"):
• Claudication symptoms: such as calf pain, leg weakness, other leg discomfort associated with activity and relieved by rest
• Chronic limb-threatening ischemia: chronic rest pain, ischemic ulcers or gangrene
• Acute limb ischemia: sudden painful, pale leg progressing to foot or leg paresthesia or paralysis
• ABI accuracy: the sensitivity and specificity of the ABI for detection of PAD with the Doppler technique range from 0.17 to 1.0 and from 0.80 to 1.0, respectively. Lower sensitivities (0.53–0.70) are reported in diabetic patients.[6][7]
• ABI limitations: for patients with diabetes mellitus, medial calcinosis, or end-stage renal disease, the American Heart Association (AHA) recommends other noninvasive tests to diagnose PAD, such as toe-brachial index or Doppler waveform.[6]
• Rationale: Diabetes mellitus, medial calcinosis, or end-stage renal disease lead to calcification of the arterial wall, which prevents detection of stenotic disease by the ABI. Vascular calcification causes the ankle artery to be incompressible and the systolic pressure at that location cannot be measured despite cuff inflation >250 mm Hg. In other cases, the ankle artery systolic pressure is measurable but is much higher than the brachial artery systolic pressure, leading to an ABI that exceeds the normal range.[6]
• For patients with an elevated ABI (>1.3), guidelines recommend measurement of the toe-brachial index.[5] The digital vessels rarely develop calcification and can provide an accurate determination of vascular disease in this setting.[5] 
• For all patients with a non-healing wound or gangrene, the AHA suggests further assessment with other noninvasive arterial tests to rule out chronic limb-threatening ischemia (i.e, with toe brachial index with waveforms, transcutaneous oximetry, skin perfusion pressure), even if the initial ABI falls within normal range.[5]  
• Rationale: Even if ABI results fall within normal range, it is important to note that values can be falsely elevated. This should be suspected if ABI is normal with a monophasic Doppler waveform or if non-healing wounds or gangrene are present.[2][8] See section 'Noninvasive arterial tests' in topic "Arterial Ulcers - Introduction and Assessment".
• For patients being considered for lower extremity compression therapy.
• The ABI rules out significant arterial disease and determines the amount of compression (if any) that can be applied safely. See topic "How to Select Adequate Compression Therapy Pressure Levels and Products".

Asymptomatic patients: to identify patients at risk for PAD 

• For individuals at elevated cardiovascular risk without leg symptoms, clinicians might opt to use ABI to screen for PAD.[1][5]
• According to guidelines however, this patient population (patients with elevated cardiovascular risk without leg symptoms) warrants intensive atherosclerosis risk factor reduction regardless of the ABI, thus performing an ABI does not alter the care plan. In addition, the false positive rate is higher in this population, as the prevalence of PAD is lower in asymptomatic high cardiovascular risk patients than patients with leg symptoms.[1][5][9][10]
• For individuals at low or moderate cardiovascular risk without leg symptoms, guidelines do not support use of ABI to screen for PAD.[1][5][9][10]

Contraindications

• Deep vein thrombosis (DVT): the AHA guidelines recommend avoiding compression of the extremity with known or suspected DVT due to concern for breaking and embolizing a thrombus. [6]
• Inability to remain supine for the duration of the examination 
• Extremity injury and other conditions (e.g. post mastectomy, post placement of a bypass graft) that prevent use of an occlusive sphygmomanometer 

HOW TO PERFORM AN ABI

An ABI can provide three types of information: 

• Numerical result: for interpretation of results, see section 'How to Interpret an ABI' below
• Doppler sound: sounds can be triphasic, biphasic and monophasic (see topic "How to Interpret Audible Handheld Doppler Ultrasound and Waveforms to Rule out PAD")
• Waveform: waveforms can be triphasic, biphasic and monophasic; waveforms show elasticity of the artery and its response to the blood flow (see topic "How to Interpret Audible Handheld Doppler Ultrasound and Waveforms to Rule out PAD") 

Steps and Rationale

The steps below illustrate how to perform a single level ABI test [11] (billable with a CPT code 93922, if all requirements are met. See section 'Coding, Coverage and Reimbursement' below). See Figure 2.

Video

• [External video] Ankle-brachial Index for Assessment of Peripheral Artery Disease 

Worksheet

• Utilize the 'ABI worksheet' to record and calculate ABI

HOW TO INTERPRET AN ABI

ABI interpretation is shown below. For interpretation of other bedside non-invasive arterial tests, see section 'Noninvasive arterial tests' in topic "Arterial Ulcers - Introduction and Assessment".

CODING, COVERAGE AND REIMBURSEMENT

Each individual Medicare insurance carrier determines the local coverage requirements for coverage of ABI. See local coverage determinations (LCD) related to noninvasive arterial tests in topic "Medicare Coverage Determinations for Wound Care".

Typically, Medicare considers an ABI part of the history and physical exam and thus does not cover ABI separately from an evaluation and management service.[15] However, an ABI may be reimbursed when derived from a more comprehensive procedure which includes a permanent chart copy of the measured pressures and waveforms in the examined vessels.[15] Note: Most Medicare carriers do not provide reimbursement for ankle waveforms generated by the older analog strip chart recorders, or for any device that does not provide a hard-copy of the waveform.

Some Medicare carriers (e.g. CGS) require an abnormal ABI before proceeding to more sophisticated or complete noninvasive arterial studies, except in patients with severe diabetes or uremia resulting in medial calcification as demonstrated by artifactually elevated ankle blood pressure.[15]

Medical necessity

In general Medicare considers noninvasive peripheral arterial examinations, performed to establish the level and/or degree of arterial occlusive disease, to be medically necessary if (1) significant signs and/or symptoms of possible limb ischemia are present and (2) the patient is a candidate for invasive/surgical therapeutic interventions.[15][16]

Some Medicare insurance carriers (e.g. Noridian) will require that noninvasive arterial and venous circulation in the extremity be confirmed within two weeks of the initial patient encounter and included in the treatment plan. Once adequacy of vascular supply is established, it is anticipated that these studies need not be repeated unless there is failure to achieve wound healing.[17]

CPT® Code

• CPT Code 93922: Limited bilateral noninvasive physiologic studies of upper or lower extremity arteries, (eg, for lower extremity: ankle/ brachial indices at distal posterior tibial and anterior tibial/ dorsalis pedis arteries plus bidirectional, doppler waveform recording and analysis at 1-2 levels, or ankle/brachial indices at distal posterior tibial and anterior tibial/dorsalis pedis arteries plus volume plethysmography at 1-2 levels, or ankle/ brachial indices at distal posterior tibial and anterior tibial/ dorsalis pedis arteries with transcutaneous oxygen tension measurements at 1-2 levels)
• When conducted at the ankle, this physiologic study has two components: 1) ABI values and 2) the bi- directional Doppler waveforms from the ankle (posterior tibial or dorsalis pedis arteries). 

• CPT Code 93923: Complete bilateral noninvasive physiologic studies of upper or lower extremity arteries, 3 or more levels (eg, for lower extremity: ankle/brachial indices at distal posterior tibial and anterior tibial/dorsalis pedis arteries plus segmental blood pressure measurements with bidirectional doppler waveform recording and analysis, at 3 or more levels, or ankle/brachial indices at distal posterior tibial and anterior tibial/dorsalis pedis arteries plus segmental volume plethysmography at 3 or more levels, or ankle/brachial indices at distal posterior tibial and anterior tibial/dorsalis pedis arteries plus segmental transcutaneous oxygen tension measurements at 3 or more level(s), or single level study with provocative functional maneuvers (eg, measurements with postural provocative tests, or measurements with reactive hyperemia)
  
• CPT Code 93924: Noninvasive physiologic studies of lower extremity arteries, at rest and following treadmill stress testing, (ie, bidirectional doppler waveform or volume plethysmography recording and analysis at rest with ankle/brachial indices immediately after and at timed intervals following performance of a standardized protocol on a motorized treadmill plus recording of time of onset of claudication or other symptoms, maximal walking time, and time to recovery) complete bilateral study
  

Credentialing and Accreditation Standards

The accuracy of non-invasive vascular diagnostic studies depends on the knowledge, skill, and experience of the technologist and interpreter. Consequently, the physician performing and/or interpreting the study must be capable of demonstrating documented training and experience. A vascular diagnostic study may be personally performed by a physician, a certified technologist, or in a certified vascular testing lab.

Typically, CMS will consider services medically reasonable and necessary only if performed by appropriately trained providers (e.g. WPS's LCD).[18]

• Most Medicare carriers require non-invasive vascular diagnostic studies be performed meeting at least one of the following:
• performed by a licensed qualified physician, or
• performed by a technician who is certified in vascular technology, or
• performed in facilities with laboratories accredited in vascular technology