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Updated: Oct 19, 2025
A High-throughput Method for Measurement of Glomerular Filtration Rate in Conscious Mice
Published on: May 10, 2013
Modified Schwartz formula and 99mTc-DTPA plasma clearance methods to calculate glomerular filtration rate in
Rohit Bhowmick1, Ramachandran Rameshkumar2, Madhusudhanan Ponnusamy3
1Division of Pediatric Critical Care, Department of Pediatrics, Jawaharlal Institute of Postgraduate Medical Education and Research (JIPMER), Puducherry, 605 006, India.
Insights
The modified Schwartz formula shows good agreement for estimating glomerular filtration rate (GFR) in critically ill children. However, the formula tends to underestimate GFR, which is important for bedside application in pediatric intensive care units.
Area of Science:
- Pediatric Nephrology
- Critical Care Medicine
- Clinical Chemistry
Background:
- Limited studies compare modified Schwartz formula estimated GFR (e-GFR) with measured GFR (m-GFR) in critically ill children.
- Accurate GFR assessment is crucial for managing fluid balance, drug dosing, and predicting outcomes in this population.
Purpose of the Study:
- To evaluate the agreement between e-GFR using the modified Schwartz formula and m-GFR in critically ill children.
- To assess the accuracy and diagnostic performance of e-GFR for acute kidney injury (AKI) compared to m-GFR.
Main Methods:
- Prospective cohort study of children aged 1 month to 12 years admitted to the ICU.
- m-GFR measured using 99mTc-DTPA renal scan; e-GFR calculated by the modified Schwartz formula.
- Analysis included bias, precision, accuracy, and agreement (intraclass correlation), and AKI incidence using p-RIFLE criteria.
Main Results:
- 208 pairs analyzed; e-GFR showed good agreement with m-GFR (intraclass correlation 74%).
- Mean bias was -4.37 ml/min/1.73 m2; e-GFR underestimated m-GFR by 19.8%.
- Accuracy within 30% was 78.8%; AKI incidence was 60.1% by e-GFR vs. 54.3% by m-GFR (kappa 0.569).
Conclusions:
- The modified Schwartz formula provides reasonable GFR estimation in critically ill children.
- Clinicians should be aware of the systematic underestimation of GFR by the modified Schwartz formula at the bedside.
- The formula demonstrates acceptable sensitivity for AKI detection in this cohort.
Background:
Studies comparing the modified Schwartz formula with measured GFR (m-GFR) are lacking in critically ill children.
Methods:
This prospective cohort study enrolled children aged 1 month to 12 years, within 24 h of admission. m-GFR measured by technetium-99m-labeled diethylenetriaminepentaacetic acid (99mTc-DTPA) and calculated by Russell's two-sample slope-intercept method. Serum creatinine was estimated by modified Jaffe method and estimated GFR (e-GFR) calculated by modified Schwartz formula. The primary outcome was to find agreement between the two methods. Bias, precision, and accuracy were calculated. Secondary outcomes were the incidence of AKI (by p-RIFLE criteria) and the difference between the two methods to diagnose AKI.
Results:
A total of 208 pairs were analyzed. e-GFR showed good agreement with m-GFR with a mean bias of -4.37 ml/min/1.73 m2 and precision (SD of bias) of 33.07, 95% limit of agreement -69.18 to 60.45, and intraclass correlation of 74% (95%CI 66-80%, P < 0.001). e-GFR underestimated m-GFR by 19.8% (95% CI 7.9-31.7%). Accuracy of e-GFR values within 10%, 20%, and 30% of m-GFR were 68.3%, 72.6%, and 78.8%, respectively. Incidence of AKI within 24 h was 60.1% by e-GFR and 54.3% by m-GFR (kappa 0.569, P < 0.001; sensitivity of 85.8%, 95%CI (78-91.7%).
Conclusions:
The modified Schwartz formula shows good agreement with 99mTc-labeled DTPA double plasma sample clearance method for calculating GFR in critically ill children aged 1 month to 12 years. The underestimation of GFR should be kept in mind while applying the formula at the bedside in PICU.
Trial Registration:
Protocol accessible at Clinical Trial Registry of India (CTRI) www.ctri.nic.in . (Trial Registered Prospectively and Registration No. CTRI/2017/10/010014) ([Registered on: 06/10/2017] Trial Registered Prospectively.) (Title "Measured glomerular filtration rate using Diethylenetriaminepentaacetic acid (DTPA) renal scan versus estimated glomerular filtration rate using modified Schwartz formula in critically ill children: A prospective observational, analytical study."). A higher resolution version of the Graphical abstract is available as Supplementary information.
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