Utility of Toe-Brachial Index

The toe-brachial index is typically an adjunctive examination to the ankle-brachial index, which has long been the primary physiologic modality for diagnosing peripheral arterial disease. The goal of this project was to determine toe-brachial index reliability, particularly with patients with diabetes. We compared duplex ultrasound to the ankle-brachial index and toe-brachial index on 100 patients (200 legs) with suspected symptomatic peripheral arterial disease. Duplex ultrasound stenosis in the femoral/popliteal/infrapopliteal arteries was at least a doubling of velocity between adjacent segments. A blunted systolic Doppler waveform was consistent with proximal occlusive disease. Normal physiologic ranges were arbitrarily set as ankle-brachial index 1.2 to 0.9 and toe-brachial index 0.9 to 0.5. We calculated overall sensitivity/specificity values by averaging. Both physiologic modalities had overall low sensitivity (ankle-brachial index 62%, toe-brachial index 56%). In diabetics, ankle-brachial index sensitivity was 61% and toe-brachial index sensitivity was 57%. Sensitivity improved in the presence of inflow disease (ankle-brachial index 78%, toe-brachial index 63%). Both modalities had good overall specificity (ankle-brachial index 96%, toe-brachial index 86%). In patients with diabetes, the ankle-brachial index specificity was 94% and toe-brachial index specificity was 79%. Both physiologic modalities had identical accuracy (0.43) in comparison to duplex ultrasound. Routine toe-brachial index in conjunction with the ankle-brachial index may not be clinically productive.