TBI or not TBI: that is the question. Is it better to measure toe pressure than ankle pressure in diabetic patients?

Aims Measurement of ankle blood pressure is a simple method of assessing lower limb arterial blood supply. However, its use in diabetes has been questioned due to the presence of medial artery calcification. Measurement of toe blood pressure has been advocated as an alternative but it is technically more difficult. The aim of this study was to obtain information to guide clinicians as to when pressure measurements should be taken at the toe. Methods Ankle brachial index (ABI) and toe brachial index (TBI) were measured by Doppler ultrasound, or photoplethysmography on 174 subjects with diabetes and 53 control subjects. The Bland and Altman method, and the Cohen's method of measuring agreement between two tests were used to compare ABI with TBI. Results The mean differences between ABI and TBI in control and diabetic subjects are +/-0.400.13 and 0.37 +/-0.15, respectively. Nearly all diabetic patients with an ABI <1.3 have an ABI-TBI gradient falling within the normal range established from the non-diabetic cohort. In contrast, the majority of diabetic subjects with an ABI <greater than or equal to>1.3 have ABI-TBI differences outside this range. When patients are categorized according to ABI and TBI, there is also good agreement between the tests when ABI is low or normal (84% and 78% agreement, respectively), but not when ABI is elevated. Conclusion In the majority of patients with diabetes, assessment of TBI conveys no advantage over ABI in determining perfusion pressure of the lower limbs. Only in those patients with overt calcification, which gives an ABI greater than or equal to1.3, are toe pressure measurements superior. This guideline should simplify assessment and treatment of diabetic patients with disease of the lower limbs.