Feasibility and reliability of measured glomerular filtration rate with [I125]-iothalamate among young adults with mild-to-moderate cerebral palsy.

Objective: Despite the need, measuring glomerular filtration rate (mGFR) is not routinely performed for adults with cerebral palsy (CP), possibly due to unknown feasibility given the secondary complications of CP. This study aimed to assess the feasibility and reliability of mGFR and explore factors associated with eGFR-mGFR discordance among young adults with mild-to-moderate CP.

Methods: This single-center, cross-sectional study included 18- to 40-year-olds with CP gross motor function classification system (GMFCS) I-III. The participants were excluded if they were pregnant/lactating, had cognitive impairments, or had contraindications to mGFR. A routine clinical protocol for mGFR and eGFR was used. mGFR feasibility was assessed based on the number of participants who completed testing. mGFR reliability was assessed using the coefficient of variation (CV) across the four 30 min intervals. The association between age, sex, and GMFCS and the percentage of eGFR-mGFR discordance was assessed.

Results: Of the 19 participants enrolled, 18 completed the testing [mean age (SD), 29.9 (7.4) years,  = 10 female participants,  = 10/3/5 for GMFCS I/II/III] and most ( = 15) of the participants had an mGFR >90 mL/min; 14 participants (77.8%) had a CV <20%, 2 had a CV between 20 and 25%, and 2 had a CV >50%. eGFR overestimated mGFR by a median (interquartile range) of approximately 17.5% (2-38%); the full range of mis-estimation was -20.5 to 174.3%. Increasing age and GMFCS levels exhibited notable, but weak-to-modest, associations with a larger eGFR-mGFR discordance.

Discussion: Obtaining mGFR was feasible and reasonably reliable within this small sample. eGFR overestimated mGFR by a notable amount, which may be associated with patient-level factors.