Annals of Clinical Biochemistry > Volume 46, Number 1 > Pp. 58-64

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Original Articles

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

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 plasma creatinine remains controversial, especially when GFR approaches normal 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 (GFR_EDTA) and iohexol (GFR_iohexol) 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 GFR_EDTA were compared with those between GFR_iohexol and GFR_EDTA.

Results: Changes between fasting and postprandial eGFR correlated significantly with corresponding changes in GFR_iohexol and GFR_EDTA. eGFR predicted GFR_EDTA less precisely (SD 19.9%) than GFR_iohexol (10.5%; P < 0.01). Although eGFR showed a poorer correlation with GFR_EDTA when GFR_EDTA > 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 GFR_iohexol to GFR_EDTA in a higher fraction of studies when GFR_EDTA > 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 GFR_iohexol for predicting GFR_EDTA. The disagreement between GFR_iohexol and GFR_EDTA illustrates the extent to which uncertainty in GFR_EDTA contributes to the performance of eGFR. eGFR performs no better at lower, compared with higher levels of GFR.

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