One limitation to the measurement of lower extremity ABI is the presence of calcified, non-compressible vessels. Patients with diabetes mellitus often have non-compressible vessels; therefore, they can have falsely elevated pressures. The size of the cuff used to obtain the pressure measurement should also be appropriate for the size of the limb. In an oversized limb, a smaller cuff will yield falsely elevated measurements of the pressure. The width of the pressure cuff used on any limb should be 20 % wider than the diameter of the limb for the most accurate measurements. In diabetic patients, the use of a toe-brachial index (TBI) is considered to be more accurate assessment of the arterial pressure. The toe pressures are obtained using a PPG on the distal toe with a small toe cuff applied proximally to measure the pressure. TBI is usually >0.8 in the normal individuals, 0.2–0.5 in patients with claudication, and <0.2 in patients with critical or severe PAD (rest pain, likely poor healing, or tissue loss).