RR-variation: the autonomic test of choice in diabetes.

RR-variation is a sensitive, reproducible, and noninvasive autonomic test. It is simple to perform and easy for both the operator and the subject. Furthermore, RR-variation correlates to known physiologic function. It therefore fulfills many of the characteristics of a practical diagnostic test. Many of the confounding factors are known, and with proper standardization the test may not only have diagnostic capabilities but also predictive value. RR-variation should be included in clinical research trials of diabetic neuropathy and should be considered in routine clinical management of the diabetic patient.