MDRD tool provides estimate of nephrotoxicity risk in radiology patients
MedWire News: Radiologists can use the modification of diet in renal disease (MDRD) equation as a reasonable estimate of glomerular filtration rate (GFR) and, thus, risk for nephrotoxicity in patients who require a contrast agent, study results show.
However, MDRD overestimated GFR, particularly at low values, leading Susan Heenan (St George's Hospital, London, UK) and colleagues to warn: "It is important that staff be aware of this bias when assessing patients in radiology departments for risks of nephrotoxicity from contrast media."
Gadolinium contrast agents, as used in magnetic resonance imaging (MRI), pose a risk for developing nephrogenic systemic fibrosis (NSF), which appears to correlate with GFR.
Guidelines recommend that GFR is assessed before administration of contrast agent for MRI scans with the following actions advised: if eGFR is less than 30 ml/min per 1.73 m2, avoid high-risk gadolinium contrast agents; between 30 ml/min per 1.73 m2 and 60 ml/min per 1.73 m2), use high-risk agents with caution; and greater than 60 ml/min per 1.73 m2, use contrast medium as normal.
The MDRD was introduced in 1999 and has become the standard recommended method of estimating GFR for radiologic purposes in the UK and elsewhere.
"The aim of this study was to investigate the use of the MDRD eGFR compared against a radionuclide GFR reference standard (rGFR)," Heenan et al comment in the journal European Radiology.
They reviewed data on 516 consecutive patients referred for an MRI scan between September 2005 and September 2008.
The range of corrected rGFR values were 5-138 ml/min per 1.73 m2, with eGFR between 8 and 149 ml/min per 1.73 m2.
Although there was a significant correlation between eGFR and rGFR, there were also significant differences in the medians.
The researchers found that eGFR overestimated rGFR with a bias (mean difference) of 10.8 ml/min per 1.73 m2 over the whole range of rGFR.
Patients with an rGFR below 30 ml/min per 1.73 m2 had a mean bias of 4.6 ml/min per 1.73 m2 (difference range −5.9 to 26.3 ml/min per 1.73 m2). The bias over the range 30 to 60 ml/min per 1.73 m2 was 13.2 ml/min per 1.73 m2 (difference range −16.8 to 88.3 ml/min per 1.73 m2). The bias was reduced at GFR values above 90 ml/min per 1.73 m2.
In 25.4% of studies, eGFR was less than 60 ml/min per 1.73 m2 compared with 40.5% of rGFR studies.
"The correlation and precision shown by our study bring confidence for using the eGFR in a radiology setting; however, a significant bias was shown with eGFR overestimating rGFR," Heenan et al comment.
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By Andrew Czyzewski