Estimation in adults of the glomerular filtration rate in [99mTc]-DTPA renography - the rate constant method

RESUMEN

The purpose of this study was to design an alternative and robust method for estimation of glomerular filtration rate (GFR) in [99mTc]-diethylenetriaminepentaacetic acid ([99mTc] -DTPA renography with a reliability not significantly lower than that of the conventional Gates' method.Methods: The method is based on renographies lasting 40 min in which regions of interest (ROIs) are manually created over selected parts of certain blood pools (e.g. heart, lungs, spleen, and liver). For each ROI the corresponding time-activity curve (TAC) was generated, decay corrected and exposed to a monoexponential fit in the time interval 10 to 40 min postinjection. The rate constant in min-1 of the monoexponential fit was denoted BETA. Following an iterative procedure comprising usually 5-10 manually created ROIs, the monoexponential fit with the maximum rate constant (BETAmax) was used for estimation of GFR.Results: In a patient material of 54 adult subjects in whom GFR was determined with multiple or one sample techniques with [51Cr]-ethylenediaminetetraacetic acid ([51Cr]-EDTA) the regression curve of standard GFR (GFRstd) (i.e. GFR adjusted to 1.73 m2 body surface area) showed a close, non-linear relationship with BETAmax with a correlation coefficient of 95 por ciento. The standard errors of estimate (SEE) were 6.6, 10.6 and 16.8 for GFRstd equal to 30, 60, and 120 ml/(minÀ1.73 m2), respectively. The corresponding SEE values for almost the same patient material using Gates' method were 8.4, 11.9, and 16.8 ml/(minÀ1.73 m2).Conclusions: The alternative rate constant method yields estimates of GFRstd with SEE values equal to or slightly smaller than in Gates' method. The two methods provide statistically uncorrelated estimates of GFRstd. Therefore, pooled estimates of GFRstd can be calculated with SEE values approximately 1.41 times smaller than those mentioned above. The reliabilities of the pooled estimate of GFRstd separately and of the multiple samples method are of the same magnitude. Therefore, [99mTc]-DTPA renography could replace the multiple samples method for GFR determination. In addition, the renography requires fewer resources from patient and staff and offers more clinical results as regards renal uptake function and renal outflow.