Comparison of glomerular filtration rate (GFR) with Tc-99m-DTPA and tubular extraction rate (TER) with Tc-99m-MAG3 in potential living kidney donors: Feasibility of a one-day protocol.

AIM: Sufficient glomerular filtration rate (GFR) is mandatory in living kidney donors (LKD) before renal transplantation (RT). Guidelines recommend exogenous GFR (e. g. Tc-99m-DTPA) besides estimated GFR by plasma creatinine (eGFR). Tc-99m-MAG3 determines split function and tubular extraction rate (TER). This study evaluated a time-efficient one-day protocol for DTPA and MAG3 in potential LKD.

METHODS

Retrospective analysis of 82 consecutive potential LKD (female, 52; age, 54 [19-73] a). DTPA GFR (Fleming formula) with blood sampling 169 (147-205) min post injection of 27 (18-59) MBq Tc-99m-DTPA. 199 (181-219) min after DTPA injection, same-day renal scintigraphy with 105 (65-150) MBq MAG3 followed (TER according to Bubeck). Sufficient GFR for RT was defined age- and sex-dependent based on British guidelines, normal TER at 70 % of age-dependent average. In 15 separate potential LKD, a blank blood sample before MAG3 injection allowed estimation of remaining DTPA counts and resulting TER error.

RESULTS

Remaining Tc-99m-DTPA blood counts during sampling for MAG3 led to median TER underestimation by 12 (IQR, 8-15) ml/min/1.73 m2. Before blood count correction, 16/82 patients had reduced TER despite sufficient GFRFleming in 13/16 patients. After correction, TER remained reduced in 9/82 patients who all had sufficient GFRFleming. 10/82 patients had insufficient eGFR (CKD-EPI) but sufficient GFRFleming. Correlation coefficient for TER and GFRFleming was ρ = 0.76, for eGFR and GFRFleming ρ = 0.61, and for TER and eGFR ρ = 0.55.

CONCLUSION

A one-day protocol for Tc-99m-DTPA GFR and MAG3 dynamic imaging is feasible. If TER is calculated, the proposed method for blood count correction may be applied. However, relevance of the TER remains questionable due to frequent discordance to GFR.