Reproducibility and repeatability of differential renal function in 4-week-old piglets

Background Congenital obstructive renal disease often requires a decision early in the child's life on whether or not surgery is required. Differential renal function (DRF) calculated from the renogram provides important information for the correct decision in this process. A recent publication cast doubt as to the reliability of the renogram in providing DRF in the young child. Aim To describe the day-to-day variation and reproducibility of the two commonly used agents for estimating DRF. Methods Within 1 week, 4-week-old pigs each underwent three examinations with both Tc-99m-DTPA and Tc-99m-DMSA. DRF values from the Tc-99m-DTPA renograms were calculated using both the area under the curve (AUC) and the Rutland-Patlak equation. Day-to-day variations in the results using different background subtraction methods were analysed using the coefficient of variation for each case and the repeatability coefficient for each type of background subtraction. Results DRF calculated from the Tc-99m-DMSA studies showed little variation, with a coefficient of variation of 3.9% in the worst case. The repeatability coefficient calculated from the 99mTc-DTPA studies using the AUC technique combined with the background subtraction method giving the least variation was 14.9% while using the Rutland-Patlak technique with its best background subtraction showed an RC of 9.4%. Conclusions The study demonstrates that DRF calculated from Tc-99m-DMSA studies have low variability and the results are highly reproducible in immature pigs. The DRF calculated from Tc-99m-DTPA renograms failed to show acceptable reproducibility when analysed using either the AUC method or the Rutland-Patlak equation.