Increasing sensitivity and specificity of Doppler sonographic detection of renal transplant rejection with serial investigation technique.

Acute rejection episodes are the most common cause leading to loss of renal grafts in the early postoperative phase. Doppler sonography presents a noninvasive tool to detect increased arterial blood flow resistance as a result of rejection. This can be measured by the increase in the resistive index (RI) and the pulsatility index (PI). In a prospective study including 65 consecutive patients we investigated whether the detection of rejection episodes is improved by determining RI or PI serially twice a week instead of performing a single examination in cases of transplant dysfunction. In 330 examinations with a color-coded Doppler device (Philips QAD 1, Philips Medical Systems Hamburg, Germany) flow profiles were obtained by means of pulse-wave Doppler over at least three interlobar arteries of the renal transplant and RI and PI were calculated. In 41 cases primary rejections were better recognized by an increase in PI compared to the preceding value than by the absolute PI value (with a sensitivity of 90%; specificity was 76% and 42% respectively). The RI was less specific (with a sensitivity of 90%; specificity was 47% for the relative RI increase and 30% for the absolute RI value). The continuous PI increase started an average of 3.3 days (95% CI-15.25 to + 1.55) before rejection was diagnosed. Vascular rejection episodes showed higher PI values than interstitial rejections (3.86 +/- 2.14 vs. 2.19 +/- 0.87; P < 0.01). The serial investigation technique of PI allows better recognition of rejection episodes than the single measurement of RI or PI performed so far. Doppler sonography recognizes rejection at an early stage.