Abstract
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Introduction: The direct measurement of renal function is necessary for management of patients with compromised renal function or those in a preoperative setting. Laboratory methods including clearance of urea, creatinine, and exogenous agents require multiple urine or blood collections, causing inconvenience. In [99mTc]Tc-DTPA renal scan, a traditional imaging method to estimate glomerular filtration rate (GFR) based on renal uptake, glomerulus-filtered [99mTc]Tc-DTPA finally accumulates in the bladder, leading to the hypothesis that accumulated bladder activity might reflect overall renal function. This study aims to verify whether bladder activity in [99mTc]Tc-DTPA renal scan can represent renal function.
Methods: This retrospective study included 201 patients who underwent [99mTc]Tc-DTPA renal scan from May 30th, 2023 to December 29th, 2023 for pre- or post-operative evaluation of renal tumors, or pre-operative evaluation for kidney donors. Patients were considered eligible when meeting the following criteria: (1) complete visualization of the entire bladder on the scan, (2) available estimated GFR (eGFR) based on CKD-EPI methods within 30 days from the renal scan, and (3) available pelvis CT for measuring bladder depth.
We assessed two key quantitative parameters on the scan: (1) GFR calculated through the original Gates’ method, and (2) bladder activity per injected activity (Abladder), defined as the ratio of bladder activity measured on post-injection 20-minute images to injected radioactivity. The bladder activity was corrected for background activity measured on the upper area of the bladder, and for soft tissue attenuation using bladder depth measured from the bladder center to posterior skin in pelvis CT. Both parameters were assessed for their correlation with eGFR, the reference standard, using Pearson’s correlation coefficient, and compared using Fisher transformation. Additionally, a subgroup analysis was performed for patients with decreased eGFR (eGFR < 90 mL/min/1.73m2).
Results: The average eGFR and Gates’ GFR were 84.3 (26.1 - 122.6) and 71.4 (25.1 - 189.3) mL/min/1.73m2, respectively. Gates’ GFR demonstrated a moderately strong correlation with eGFR (Figure 1) (r = 0.494, [0.402 - 0.681], p < 0.001). Abladder, ranging from 4.45% to 56.6% (average of 21.8%), exhibited a comparable correlation with eGFR (Figure 2) (r = 0.591, [0.540 - 0.818], p < 0.001). There was no significant difference between the methods (p = 0.171). Notably, among patients with decreased eGFR (< 90 mL/min/1.73m2), Abladder showed a stronger correlation with eGFR in comparison to Gates’ GFR (r = 0.598 [0.507 - 0.872] vs. 0.396 [0.236 - 0.602], p = 0.040).
Conclusions: This pilot study demonstrated the promise of utilizing bladder activity measurement in [99mTc]Tc-DTPA renal scan as a new method for assessing renal function, especially in patients with impaired renal function. Further research involving a larger cohort and more reliable reference methods is essential to substantiate the clinical effectiveness of this approach.
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