Introduction: Accurate assessment of glomerular filtration rate (GFR) is a critical component in the evaluation of renal function in pediatric solid organ transplant recipients, as alterations in GFR may necessitate therapeutic adjustments and have significant prognostic implications for graft survival. In clinical practice, GFR is commonly estimated using various formula-based approaches; however, the reference standard remains inulin clearance, which is impractical for routine use. As an alternative, our institution employs GFR measurement via Tc-99m-DTPA, a validated method with performance comparable to the gold standard.
Methods: We conducted a cross-sectional study at a tertiary care center from August 2023 to December 2024. Inclusion criteria encompassed all pediatric patients with solid organ transplants under nephrology follow-up.
During a single study visit, GFR was measured using Tc-99m-DTPA clearance. Simultaneously, serum biochemistry (electrolytes, creatinine, and cystatin C) and urinalysis (proteinuria, albuminuria, and alpha-1 microglobulin) were performed. Additionally, calcineurin inhibitor trough levels and blood pressure measurements were obtained.
Results: 19 patients (6 females, 13 males) were enrolled: 7 heart transplant recipients, 10 liver transplant, and 2 multivisceral transplant. The median age at evaluation was 8.3 years (range 1.7–19.1 years; IQR 11.4), with a median post-transplant duration of 2.59 years (range 0.03–15.6 years; IQR 10).
Table 1  summarizes the GFR values obtained via Tc-99m-DTPA and the various estimation formulas, including the relative error percentage of each formula against the reference method and the proportion of patients with estimation deviations exceeding 10%. Creatinine-based formulas demonstrated the closest agreement with Tc-99m-DTPA measurements; however, none achieved satisfactory accuracy in this cohort.

The median tacrolimus trough level was 5.4 ng/mL (range 3–11.9), and the median corticosteroid dose was 0.1 mg/kg/day (range 0–0.23). Hypertension was present in 63% of the cohort, managed with one to two antihypertensive agents.
Conclusions: None of the estimation formulas demonstrated sufficient accuracy when compared to Tc-99m-DTPA clearance. Further studies with larger sample sizes or alternative reference methodologies are warranted to optimize GFR assessment in this population.