Clinical Application of the Kidney to Aortic Blood Flow Index (K/A Ratio)1

Abstract

The kidney to aortic blood flow index (K/A ratio) is the ratio of the slopes of the upstrokes of renal and aortic histograms, derived from regions of interest applied to sequential gamma camera images of the first transit of a 99mTc bolus. This index proved in our previous dog studies to have a good correlation with renal artery blood flow. In the 190 clinical studies of renal allografts reported here, the K/A ratios correlate well with independently established retrospective clinical-pathologic assessment of renal functional status. Normal range for the K/A ratio was established in 50 patients with no demonstrable renal disease. Tests of inter-observer reproducibility show a mean relative standard deviation of 7% for independently performed analyses on the same data.