Glomerular filtration rate what is the rationale and justification of normalizing GFR for body surface area?

Geddes, Colin C.; Woo, Y. Mun; Brady, Stefan

doi:10.1093/ndt/gfm662

Cited by 48 publications

(42 citation statements)

References 15 publications

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“…16 However, the error may be larger for individuals with atypical body sizes. 17 The alternative method proposed by Turner and Reilly on the basis of regression analysis overcomes some of the problems associated with the ratio method, because it completely removes variation associated with the variable used to adjust the GFR.…”

Section: Discussionmentioning

confidence: 99%

GFR Normalized to Total Body Water Allows Comparisons across Genders and Body Sizes

Eriksen

Melsom

Mathisen

et al. 2011

Journal of the American Society of Nephrology

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The normalization of GFR to a standardized body-surface area of 1.73 m 2 impedes comparison of GFR across individuals of different genders, heights, or weights. Ideally, GFR should be normalized to a parameter that best explains variation in GFR. Here, we measured true GFR by iohexol clearance in a representative sample of 1627 individuals from the general population who did not have diabetes, cardiovascular disease, or kidney disease. We also estimated total body water (TBW), extracellular fluid volume, lean body mass, liver volume, metabolic rate, and body-surface area. We compared two methods of normalizing GFR to these physiologic variables: (1) the conventional method of scaling GFR to each physiologic variable by simple division and (2) a method based on regression of the GFR on each variable. TBW explained a higher proportion of the variation in GFR than the other physiologic variables. GFR adjusted for TBW by the regression method exhibited less dependence on gender, height, and weight compared with the other physiologic variables. Thus, adjusting GFR for TBW by the regression method allows direct comparisons between individuals of different genders, weights, and heights. We propose that regression-based normalization of GFR to a standardized TBW of 40 L should replace the current practice of normalizing GFR to 1.73 m 2 of body-surface area.

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Section: Discussionmentioning

confidence: 99%

GFR Normalized to Total Body Water Allows Comparisons across Genders and Body Sizes

Eriksen

Melsom

Mathisen

et al. 2011

Journal of the American Society of Nephrology

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“…It has been pointed out recently that no gold standard is available to determine which indexing factor is best (12) and that the best indexing factor for GFR would be the one that provides the best clinical validity. Final proof whether ECFV is indeed the best indexing factor for GFR should therefore be provided by long-term follow-up studies in which superiority of GFR/ECFV as predictor of renal outcome is studied.…”

Section: Discussionmentioning

confidence: 99%

“…Second, it has been proposed that the best way to normalize GFR between different individuals would be by ECFV rather than by body surface area (BSA) (6,10,11). Whereas normalizing GFR for ECFV would be attractive from a theoretical perspective, it has not gained acceptance in practice because it is considered too cumbersome (12). Validation of GFR measurement protocols for simultaneous assessment of ECFV would greatly increase the feasibility of normalizing GFR for ECFV.…”

mentioning

confidence: 99%

Feasibility and Impact of the Measurement of Extracellular Fluid Volume Simultaneous with GFR by 125I-Iothalamate

Visser¹,

Muntinga²,

Dierckx³

et al. 2008

Clinical Journal of the American Society of Nephrology

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The feasibility, validity, and possible applications of the assessment of extracellular fluid volume (ECFV) simultaneous with glomerular filtration rate (GFR) were assessed in a series of validation studies using the constant infusion method of 125 T he gold standard for measuring glomerular filtration rate (GFR) is by specific tracers, such as inulin, Cr-EDTA, iothalamate, and iohexol (1). Because the distribution volume (V d ) of these tracers for GFR ideally equal extracellular fluid volume (ECFV) (2-9), measuring GFR with such tracers could potentially be used for simultaneous assessment of ECFV.Simultaneously measuring ECFV and GFR has several advantages. First, it will allow better insight into the (patho)physiologic and clinical role of ECFV in renal disease and its complications, such as hypertension and left ventricular hypertrophy. Second, it has been proposed that the best way to normalize GFR between different individuals would be by ECFV rather than by body surface area (BSA) (6,10,11). Whereas normalizing GFR for ECFV would be attractive from a theoretical perspective, it has not gained acceptance in practice because it is considered too cumbersome (12). Validation of GFR measurement protocols for simultaneous assessment of ECFV would greatly increase the feasibility of normalizing GFR for ECFV.Various GFR tracers were used for measuring ECFV (2-9), but their validation, reproducibility, and calibration against a gold standard for ECFV are not well documented. In our center, accurate GFR measurement is performed as the clearance of 125 I-iothalamate (IOT) by the constant infusion method, simultaneously with the determination of effective renal plasma flow (ERPF) (13). This renal function measurement is used in topclinical care and for clinical research and allows estimating GFR with a day-to-day variability of only 2.5% (14). The aim of the current study was to validate this renal function protocol for assessing ECFV and to use the combined assessment for normalizing GFR to ECFV. To this purpose, we studied first, the agreement of V d IOT with V d of bromide, the golden standard for ECFV measurements, over a wide range of renal function. Second, we assessed the reproducibility of ECFV measurements by assessing V d IOT under conditions of standardized sodium intake in healthy volunteers. Third, in these volunteers we tested the sensitivity of V d IOT to detect a change in ECFV. Finally, we analyzed the impact of indexing GFR to ECFV in the above volunteers and in a cohort of 158 potential kidney donors. Materials and MethodsAll experiments were performed in adherence to the Declaration of Helsinki, approved by the Medical Ethics Committee of the University Medical Centre Groningen, and all participating subjects gave written informed consent for participation. Measurement of Renal FunctionRenal function measurements were performed using the constant infusion method with IOT and 131 I-Hippuran as described before (13-15). After drawing a time point-0 blood sample, a priming solution

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“…Early findings suggest that modifications of the original MDRD formula will be required in these populations (13). Correction of eGFR to a standard body surface area (BSA), explicitly included in the MDRD formula, may also give rise to errors when the individual are very obese or very lean (14) Widespread and uncritical use of the current K/DOQI advocated MDRD formula without modifications can, and likely will, lead to erroneous estimates of the population-wide prevalence of CKD. The issue of "calibration" of serum creatinine measurements to a single "global gold-standard" has been vigorously discussed elsewhere (15).…”

Section: Egfr Is Unreliable In Defining Ckdmentioning

confidence: 99%

“…Elderly subjects may have a reduction in TBW (17). If the absolute value for eGFR is a more important parameter for determining drug dosage, then adjustment for BSA may give rise to errors in the obese and the lean, independent of age (14,16). Absolute true GFR values will be underestimated in the obese and overestimated in the very lean.…”

Section: Egfr Is Unreliable In Defining Ckdmentioning

confidence: 99%

Screening for CKD with eGFR

Glassock

Winearls

2008

Clinical Journal of the American Society of Nephrology

157

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The early identification of chronic kidney disease (CKD) is a legitimate enterprise if it provides meaningful opportunities for effective and safe interventions that reduce the risk of death, end-stage renal disease, or complications of renal dysfunction. The screening of unselected populations not already known to be at risk of CKD has the potential of harm and has not been shown to be cost-effective. The application of formulas for the estimation of GFR (eGFR) to the guidelines for staging of chronic kidney disease (Kidney Disease Outcomes Quality Initiative, K/DOQI) as universal screening tools is of dubious value and has inherent dangers. This conclusion is based both on the unreliability of current formulas for determining eGFR and flaws in the K/DOQI schema for staging of CKD. The failure to take into account the normal age-and gender-associated decline in GFR and the lack of a requirement for other evidence of kidney disease in CKD stage 3 leads to an erroneous categorization of large numbers of mostly elderly and female subjects as having an intermediate stage of a lethal disease. Criteria for CKD staging should take into account the percentile distribution of eGFR by age and gender. Targeted screening for CKD is likely to be more cost-effective than universal screening. Whether early identification and treatment of subjects with "reduced" levels of GFR within the normal range for their age/gender, but without any other manifestations of kidney disease, will reduce the subsequent risk of cardiovascular events or progression to end-stage-renal disease is currently unproven.

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Glomerular filtration rate what is the rationale and justification of normalizing GFR for body surface area?

Cited by 48 publications

References 15 publications

GFR Normalized to Total Body Water Allows Comparisons across Genders and Body Sizes

GFR Normalized to Total Body Water Allows Comparisons across Genders and Body Sizes

Feasibility and Impact of the Measurement of Extracellular Fluid Volume Simultaneous with GFR by 125I-Iothalamate

Screening for CKD with eGFR

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