Estimating renal function from the visual analysis of Tc-99m DTPA images

Eleven visual parameters of Tc-99m DTPA imaging studies were evaluated to identify scintigraphic findings that best detect changes in renal function, to determine at which GFR levels they appear, and to establish criteria for visual estimation of renal function. Visual parameters were compared to in vitro GFR determinations in 41 patients. Three visual parameters offered best discrimination. The first one appeared at GFR values below 70 mL/min (sensitivity: 76%). The renal peak activity on the flow study (normally equal or greater than aortic) no longer reached the intensity of the aortic peak (pK < pA). The second parameter appeared at GFR values below 50 mL/min (sensitivity: 85%). The estimated kidney-to-liver ratio in the 2-minute image (usually 3 or greater) decreased to values less than 3. The third scintigraphic finding, pelvicalyceal system nonvisualization, appeared at GFR levels below 20 mL/min (sensitivity 100%). Use of these 3 scintigraphic findings allows categorization of patients into four functional groups: 1) severe dysfunction (GFR: 0-20 mL/min), 2) moderate to severe dysfunction (GFR: 21-50 mL/min), 3) moderate dysfunction (GFR: 50-70 mL/min), and 4) Normal study (GFR > 70 mL/min). Visual analysis of Tc-99m DTPA images does not identify patients with mildly decreased renal function (GFR: 70-90 mL/min).