Simultaneous glomerular filtration rate determination using inulin, iohexol, and 99m Tc-DTPA demonstrates the need for customized measurement protocols.
Level 3 - non-randomized controlled study
Prospective diagnostic accuracy and method-comparison study comparing plasma tracer clearance protocols against simultaneous urinary inulin clearance.
PubMed 32750458 · doi:10.1016/j.kint.2020.06.044
What was done
Researchers measured glomerular filtration rate (GFR) simultaneously using urinary inulin clearance (gold standard), plasma iohexol, and plasma 99mTc-DTPA in 77 participants. Blood was sampled across multiple time points from 2 to 10 hours post-injection. Bias, precision, and accuracy metrics (P30 and mean absolute error) were evaluated for different sampling schedules across eGFR subgroups (<30, 30–59, and ≥60 ml/min/1.73 m²) and edema status.
What was found
The mean inulin GFR of the cohort was 33 ml/min/1.73 m². For plasma iohexol, delaying both the initial and final blood samples yielded the highest accuracy in patients with low GFR (<30 ml/min/1.73 m²), whereas earlier initial and final samples were most accurate in patients with higher GFR (≥60 ml/min/1.73 m²). None of the tested plasma sampling protocols achieved acceptable accuracy in patients with edema. Exact numerical values for bias, precision, and P30 were not reported in the abstract.
Why it matters
Plasma clearance protocols cannot use a single universal sampling schedule without losing accuracy. Tailoring blood sampling times to baseline expected GFR improves measurement accuracy, while standard plasma clearance methods remain unreliable in edematous patients.
Limits
The sample size was small (77 participants) with an overall low mean GFR (33 ml/min/1.73 m²), limiting power in higher GFR subgroups. The abstract does not provide exact numerical accuracy statistics (P30, MAE, or bias) or specific 99mTc-DTPA protocol metrics, and external validation was not reported.
Cited by
- supports Inulin clearance is the gold standard method for measuring glomerular filtration rate.