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Published on: May 10, 2013
Determination of Glomerular Filtration Rate After Contrast-Enhanced CT Among Critically Ill Patients: Support for a
Bertil Kågedal1, Anders Helldén1,2, Dženeta Nezirević Dernroth1
1Department of Biomedical and Clinical Science, Division of Clinical Chemistry and Clinical Pharmacology, Linköping University, Linköping, Sweden.
Insights
Glomerular filtration rate (GFR) measured with iohexol plasma clearance after CT scans closely aligns with urinary creatinine clearance in critically ill patients. Estimated GFR calculations using creatinine and cystatin C showed significant over- and underestimations, respectively.
Area of Science:
- Nephrology
- Critical Care Medicine
- Diagnostic Imaging
Background:
- Accurate measurement of glomerular filtration rate (GFR) is crucial for managing critically ill patients.
- Traditional methods for GFR estimation can be unreliable in intensive care unit (ICU) settings.
- Iohexol plasma clearance offers a potential method for precise GFR assessment.
Purpose of the Study:
- To determine GFR using iohexol plasma clearance (mGFRiohexol) in critically ill patients following high-dose administration during CT scans.
- To evaluate the agreement between mGFRiohexol and urinary creatinine clearance (uClcr).
- To compare mGFRiohexol with estimated GFRs (eGFRs) derived from plasma creatinine (eGFRcr) and cystatin C (eGFRcys).
Main Methods:
- A prospective observational cohort study was conducted in ICUs.
- Twenty-six critically ill adult patients received high-dose iohexol for contrast-enhanced CT.
- Plasma iohexol concentrations were measured to calculate mGFRiohexol; uClcr and eGFRcr/eGFRcys were also determined.
Main Results:
- Mean mGFRiohexol was 77.4 ± 38.1 mL/min, while mean uClcr was 97.3 ± 58.2 mL/min.
- Strong positive correlations were observed between high-dose and low-dose mGFRiohexol (R² = 0.88) and between mGFRiohexol and uClcr (R² = 0.87).
- eGFRcr overestimated mGFRiohexol, whereas eGFRcys underestimated it.
Conclusions:
- mGFRiohexol determined after contrast-enhanced CT shows good agreement with low-dose iohexol clearance and uClcr.
- Discrepancies in eGFRcr and eGFRcys likely stem from altered tubular secretion of creatinine and cystatin C production in ICU patients.
- Iohexol plasma clearance is a reliable method for assessing GFR in critically ill patients.
Objectives:
To measure glomerular filtration rate using iohexol plasma clearance (mGFRiohexol) in critically ill patients using the high doses of iohexol administered at CT and to evaluate its agreements with urinary creatinine clearance (uClcr) and estimated glomerular filtration rates (eGFRs), calculated from plasma concentrations of creatinine (eGFRcr) and cystatin C (eGFRcys).
Design:
Prospective observational cohort study.
Setting:
ICUs across Southeast Sweden.
Patients:
Critically ill adult patients.
Interventions And Measurements:
Twenty-six ICU patients were given high doses of iohexol (range, 27-140 mL) for contrast-enhanced CT, whereafter blood samples were taken in the elimination phase for determination of mGFRiohexol. Plasma iohexol concentrations were determined by high-performance liquid chromatography and mGFRiohexol was calculated. Standard dose (5 mL) of iohexol was administered the following days to compare low-dose clearance results with the high-dose clearance results. Six-hour uClcr was performed four times a day and averaged.
Main Results:
Mean ± sd mGFRiohexol after CT was 77.4 ± 38.1 mL/min (n = 26), and uClcr was 97.3 ± 58.2 mL/min (n = 25) in the critically ill patients. There was a strong positive correlation between mGFRiohexol determined with high and low doses of iohexol in patients with normal or high mGFRiohexol (coefficient of determination [R2] = 0.88; p < 0.001) and between mGFRiohexol and uClcr (R2 = 0.87; p < 0.001). eGFRcr overestimated mGFRiohexol and eGFRcys underestimated mGFRiohexol.
Conclusions:
mGFRiohexol after contrast-enhanced CT compares well with mGFRiohexol after standard low-dose iohexol respectively uClcr. Over- and underestimation of mGFRiohexol by eGFRcr and eGFRcys is probably explained by increased tubular secretion of creatinine and increased production of cystatin C in intensive care patients.
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