What is considered an abnormal resistive index (RI)?

The resistive index (RI) is a measurement derived from Doppler ultrasound that assesses blood flow in vessels, particularly in the kidneys and other organs. It is calculated using the formula RI = (peak systolic velocity - end diastolic velocity) / peak systolic velocity. This index helps to evaluate the resistance to blood flow, often in the context of vascular health and perfusion.

An abnormal RI generally indicates some level of vascular compromise or pathology. Typically, a resistive index value less than 0.8 is considered normal, meaning that blood flow is more consistent with healthy perfusion patterns. Values greater than or equal to 0.8 suggest an increase in resistance, which can be indicative of conditions such as renal artery stenosis or other forms of vascular impairment.

When the RI is assessed in a clinical setting and found to be greater than or equal to 0.8, this can raise concerns about the functionality of the vascular bed being evaluated. Such values signify that there may be increased resistance in the small arteries, potentially due to a variety of pathological processes affecting blood flow.

This understanding of the normal ranges for RI is critical for making informed decisions in clinical practice regarding the presence of vascular disease or damage.