Evaluation of the Modification of Diet in Renal Disease equation (eGFR) against simultaneous, dual-marker multi-sample measurements of glomerular filtration rate

Ann Clin Biochem 2009;46:58-64
© 2009 Association for Clinical Biochemistry


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Original Articles

A Michael Peters1,
Nicholas J Bird1,
Ian Halsall2,
Christina Peters1 and
A Robert Michell3

1 Department of Nuclear Medicine;
2 Department of Clinical Biochemistry and Immunology, Addenbrooke’s Hospital, Cambridge;
3 William Harvey Research Institute, Department of Biochemical Pharmacology, St Bartholomew’s Medical School, London, UK

Corresponding author: Prof A M Peters, Audrey Emerton Building, Royal Sussex County Hospital, Eastern Road, Brighton BN2 5BE, UK. Email: a.m.peters{at}bsms.ac.uk

Background: Estimation of glomerular filtration rate (GFR) using plasmacreatinine remains controversial, especially when GFR approachesnormal values. The aim was to re-examine estimated GFR (eGFR)using dual-reference GFR measurements.

Methods: eGFR (simplified modified Modification of Diet in Renal Disease equation) was compared with GFR measured with iohexol for predicting GFR measured with 51Cr-ethylenediaminetetraacetic acid (EDTA). Dual six-sample GFR (20–240 min postinjection) was measured in 60 patients and 20 normal volunteers with 51Cr-EDTA (GFREDTA) and iohexol (GFRiohexol) injected into separate arms and sampled contralaterally. This was repeated in the normal volunteers under fasting conditions (twice in nine). Percentage bias, imprecision (SD of bias) and disagreement (sign-less difference) between eGFR and GFREDTA were compared with those between GFRiohexol and GFREDTA.

Results: Changes between fasting and postprandial eGFR correlated significantly with corresponding changes in GFRiohexol and GFREDTA. eGFR predicted GFREDTA less precisely (SD 19.9%) than GFRiohexol (10.5%; P < 0.01). Although eGFR showed a poorer correlation with GFREDTA when GFREDTA > 80 mL/min/1.73 m2 compared with <80 mL/min/1.73 m2, there was no significant difference with respect to imprecision or disagreement of >20 or 30%. However, eGFR was closer than GFRiohexol to GFREDTA in a higher fraction of studies when GFREDTA > 80 mL/min/1.73 m2 (28/60) than when it was <80 mL/min/1.73 m2 (9/37; P < 0.05).

Conclusion: eGFR is inferior to GFRiohexol for predicting GFREDTA. The disagreement between GFRiohexol and GFREDTA illustrates the extent to which uncertainty in GFREDTA contributes to the performance of eGFR.eGFR performs no better at lower, compared with higher levelsof GFR.

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