External validation of the Berlin equations for estimation of GFR in the elderly

Comparison of the applicability of seven calculation equations of glomerular filtration rate among elderly people in China

BACKGROUND

At present, estimated glomerular filtration rate (eGFR) remains the most frequently utilized parameter in the evaluation of kidney injury severity. Numerous equations have been formulated based on serum creatinine (Scr) or serum cystatin C (Cysc) levels. However, there is a lack of consensus regarding the efficacy of these equations in assessing eGFR, particularly for elderly individuals in China. This study aimed to evaluate the applicability of the MDRD, MDRDc, CKD-EPI series, BIS1, and FAS equations within the Chinese elderly population.

METHODS

A cohort of 298 elderly patients with measured GFR (mGFR) was enrolled. The patients were categorized into three subgroups based on their mGFR levels. The eGFR performance was examined, taking into account bias, interquartile range (IQR), accuracy P30, and root-mean-square error (RMSE). Bland-Altman plots were employed to verify the validity of eGFR.

RESULTS

The participants had a median age of 71 years, with 167 (56.0%) being male. Overall, no significant differences in bias were observed among the seven equations (P > 0.05). In terms of IQR, P30, and RMSE, the BIS1 equation demonstrated superior accuracy (14.61, 72.1%, and 13.53, respectively). When mGFR < 30 ml/min/1.73 m2, all equations underestimated the true GFR, with the highest accuracy reaching only 59%. Bland-Altman plots indicated that the BIS1 equation exhibited the highest accuracy, featuring a 95% confidence interval (CI) width of 52.37.

CONCLUSIONS

This study suggested that the BIS1 equation stands out as the most applicable for estimating GFR in Chinese elderly patients with normal renal function or only moderate decline. 2020NL-085-03, 2020.08.10, retrospectively registered.

Comparison of glomerular filtration rate estimating equations in older adults: A systematic review and meta-analysis

BACKGROUND

Debates persist regarding the performance of existing glomerular filtration rate (GFR) estimating equations in older individuals. We performed this meta-analysis to assess the accuracy and bias of six commonly used equations, including the Chronic Kidney Disease Epidemiology Collaboration creatinine equation (CKD-EPICr) and its combination with cystatin C (CKD-EPICr-Cys), with the corresponding pair of the Berlin Initiative Study equations (BIS1 and BIS2) and the Full Age Spectrum equations (FASCr and FASCr-Cys).

METHODS

PubMed and the Cochrane Library were searched for studies comparing estimated GFR (eGFR) with measured GFR (mGFR). We analyzed the difference in P30 and bias among the six equations and investigated subgroups based on the area (Asian and non-Asian), mean age (60-74 years and ≥75 years), and levels of mean mGFR (<45 mL/min/1.73m2 and ≥45 mL/min/1.73m2).

RESULTS

27 studies with 18,112 participants were included, all reporting P30 and bias. BIS1 and FASCr exhibited significantly higher P30 than CKD-EPICr. While no significant differences were observed between FASCr and BIS1, or among the three combined equations in terms of either P30 or bias. Subgroup analyses revealed FASCr and FASCr-Cys achieved better results in most situations. However, in the subgroup of mGFR<45 mL/min/1.73m2, CKD-EPICr-Cys had relatively higher P30 and significantly smaller bias.

CONCLUSIONS

Overall, BIS and FAS provided relatively more accurate estimates of GFR than CKD-EPI in older adults. FASCr and FASCr-Cys may be better suited for various conditions, while CKD-EPICr-Cys would be a better option for older individuals with impaired renal function.

A back propagation neural network approach to estimate the glomerular filtration rate in an older population

BACKGROUND

The use of creatinine-based glomerular filtration rate (GFR)-estimating equations to evaluate kidney function in elderly individuals does not appear to offer any performance advantages. We therefore aimed to develop an accurate GFR-estimating tool for this age group.

METHODS

Adults aged ≥ 65 years who underwent GFR measurement by technetium-99 m-diethylene triamine pentaacetic acid (^99mTc-DTPA) renal dynamic imaging were included. Data were randomly split into a training set containing 80% of the participants and a test set containing the remaining 20% of the subjects. The Back propagation neural network (BPNN) approach was used to derive a novel GFR estimation tool; then we compared the performance of the BPNN tool with six creatinine-based equations (Chronic Kidney Disease-Epidemiology Collaboration [CKD-EPI], European Kidney Function Consortium [EKFC], Berlin Initiative Study-1 [BIS1], Lund-Malmö Revised [LMR], Asian modified CKD-EPI, and Modification of Diet in Renal Disease [MDRD]) in the test cohort. Three equation performance criteria were considered: bias (difference between measured GFR and estimated GFR), precision (interquartile range [IQR] of the median difference), and accuracy P30 (percentage of GFR estimates that are within 30% of measured GFR).

RESULTS

The study included 1,222 older adults. The mean age of both the training cohort (n = 978) and the test cohort (n = 244) was 72 ± 6 years, with 544 (55.6%) and 129 (52.9%) males, respectively. The median bias of BPNN was 2.06 ml/min/1.73 m², which was smaller than that of LMR (4.59 ml/min/1.73 m²; p = 0.03), and higher than that of the Asian modified CKD-EPI (-1.43 ml/min/1.73 m²; p = 0.02). The median bias between BPNN and each of CKD-EPI (2.19 ml/min/1.73 m²; p = 0.31), EKFC (-1.41 ml/min/1.73 m²; p = 0.26), BIS1 (0.64 ml/min/1.73 m²; p = 0.99), and MDRD (1.11 ml/min/1.73 m²; p = 0.45) was not significant. However, the BPNN had the highest precision IQR (14.31 ml/min/1.73 m²) and the greatest accuracy P30 among all equations (78.28%). At measured GFR < 45 ml/min/1.73 m², the BPNN has highest accuracy P30 (70.69%), and highest precision IQR (12.46 ml/min/1.73 m²). The biases of BPNN and BIS1 equations were similar (0.74 [-1.55-2.78] and 0.24 [-2.58-1.61], respectively), smaller than any other equation.

CONCLUSIONS

The novel BPNN tool is more accurate than the currently available creatinine-based GFR estimation equations in an older population and could be recommended for routine clinical use.

Age-adjusted reference values and influencing factors of cystatin C in healthy Chinese population

BACKGROUND

Normative distribution of serum cystatin C and relationship with sex and age in healthy adult Chinese population is unknown.

METHODS

This is a prospective cohort study. Adult subjects (18 years of age and older) who underwent annual health examination at the Health Management Center in Sir Run Run Hospital were eligible. Subjects with major diseases, e.g., hypertension, diabetes, chronic kidney disease, obesity (body mass index ≥ 28 kg/m²) were excluded from the analysis. Multivariate logistic regression analysis was conducted to identify risk factors of elevated cystatin C (> 1.03 mg/L). Data are shown as median and 95% confidence interval (CI).

RESULTS

The final analysis included a total of 10,640 subjects (40 ± 12 years, 52% men). The median serum cystatin C concentration was 0.73 mg/L (95% CI 0.52-1.03 mg/L) in the overall analysis, 0.79 (95% CI 0.59-1.07 mg/L) in men, and 0.67 (95% CI 0.49-0.95 mg/L) in women. In the multivariate regression analysis, elevated cystatin C was independently associated with the male sex (odds ratio 1.94; 95% CI 1.07-3.52), older age (odds ratio 1.04 every year; 95% CI 1.02-1.06), higher body mass index (odds ratio 1.70; 95% CI 1.01-2.83), uric acid (odds ratio 1.00; 95% CI 1.00-1.01), and β2-microglobulin (odds ratio 39.35; 95% CI 22.90-67.64).

CONCLUSION

The median serum cystatin C concentration was 0.73 (95% CI 0.52-1.03 mg/L) in healthy adult Chinese population, 0.79 (95% CI 0.59-1.07 mg/L) in men, and 0.67 (95% CI 0.49-0.95 mg/L) in women. Elevated cystatin C was associated with the male sex, older age and higher body mass index.

The effects of aging on the renal function of a healthy population in Beijing and an evaluation of a range of estimation equations for glomerular filtration rate

We investigated how age affected renal function in healthy subjects in Beijing and compared different estimated glomerular filtration rate (eGFR) equations. Kidney function was evaluated by five equations: Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI); Modification of Diet in Renal Disease Study (MDRD); the Chinese version of the MDRD (MDRDc); Full Age Spectrum (FAS); and Berlin Initiative Study (BIS). A total of 46,708 subjects were enrolled and followed-up for 3 years. All showed an increase in sCr and a reduction in eGFR with increasing age. Over the 3 years, the eGFR and serum creatinine (sCr) remained unchanged in most subjects. Different equations showed good consistency; the intraclass correlation coefficients (ICC) was 0.849 for males, and 0.817 for females. The CKD-EPI equation yielded higher GFR values than the other equations (according to sCr levels). For subjects aged over 70 years, the BIS equation produced the lowest eGFR values. In summary, we observed that the renal function of individuals was relatively stable with increasing age, although different eGFR equations yielded data that varied across different populations of subjects and sCr levels.

Level and Change in N-Terminal Pro-B-Type Natriuretic Peptide and Kidney Function and Survival to Age 90

BACKGROUND

Many traditional cardiovascular risk factors do not predict survival to very old age. Studies have shown associations of estimated glomerular filtration rate (eGFR) and N-terminal pro-B-type natriuretic peptide (NT-pro-BNP) with cardiovascular disease and mortality in older populations. This study aimed to evaluate the associations of the level and change in eGFR and NT-pro-BNP with longevity to age 90 years.

METHOD

The population included participants (n = 3,645) in the Cardiovascular Health Study, aged between 67 and 75 at baseline. The main exposures were eGFR, calculated with the Berlin Initiative Study (BIS) 2 equation, and NT-pro-BNP, and the main outcome was survival to age 90. Mixed models were used to estimate level and change of the main exposures.

RESULTS

There was an association between baseline level and change of both eGFR and NT-pro-BNP and survival to 90, and this association persisted after adjustment for covariates. Each 10 mL/min/1.73 m2 higher eGFR level was associated with an adjusted odds ratio (OR) of 1.23 (95% CI: 1.13, 1.34) of survival to 90, and a 0.5 mL/min/1.73 m2 slower decline in eGFR was associated with an OR of 1.51 (95% CI: 1.31, 1.74). A twofold higher level of NT-pro-BNP level had an adjusted OR of 0.67 (95% CI: 0.61, 0.73), and a 1.05-fold increase per year in NT-pro-BNP had an OR of 0.53 (95% CI: 0.43, 0.65) for survival to age 90.

CONCLUSION

eGFR and NT-pro-BNP appear to be important risk factors for longevity to age 90.

Alterations in drug disposition in older adults: a focus on geriatric syndromes

INTRODUCTION

Age-associated physiological changes can alter the disposition of drugs, however, pathophysiological changes associated with geriatric syndromes in older adults may lead to even greater heterogeneity in pharmacokinetics. Geriatric syndromes are common health problems in older adults which have multifactorial causes and do not fit into distinct organ-based disease categories. With older adults being the greatest users of medications, understanding both age- and geriatric syndrome-related changes is important clinically to ensure safe and effective medication use.

AREAS COVERED

This review provides an overview of current evidence regarding pharmacokinetic alterations that occur with aging and in common geriatric syndromes, including frailty, sarcopenia, dementia, polypharmacy and enteral feeding. The evidence is presented according to the four primary pharmacokinetic processes (Absorption, Distribution, Metabolism and Excretion).

EXPERT OPINION

There is some evidence to inform our understanding of the impact of chronological aging and various geriatric syndromes on drug disposition. However, many areas require more research, including drug induced inhibition and induction of cytochrome P450 enzymes and the clinical utility of emerging methods for estimating renal function. There is a need to develop tools to predict alterations in drug disposition in subgroups of older adults, particularly where the currently available clinical information is sparse.

Chronic kidney disease in the context of multimorbidity patterns: the role of physical performance : The screening for CKD among older people across Europe (SCOPE) study

Background

Chronic kidney disease (CKD) is known to be associated with several co-occurring conditions. We aimed at exploring multimorbidity patterns associated with CKD, as well as the impact of physical performance and CKD severity on them in a population of older outpatients.

Methods

Our series consisted of 2252 patients enrolled in the Screening of CKD among Older People across Europe multicenter observational study. Hypertension, stroke, transient ischemic attack, cancer, hip fracture, osteoporosis, Parkinson’s disease, asthma, chronic obstructive pulmonary disease, congestive heart failure, angina, myocardial infarction, atrial fibrillation, anemia, CKD (defined as GFR < 60, < 45 or < 30 ml/min/1.73 m²), cognitive impairment, depression, hearing impairment and vision impairment were included in the analyses. Physical performance was assessed by the Short Physical Performance Battery (SPPB) and used as stratification variable. Pairs of co-occurring diseases were analyzed by logistic regression. Patterns of multimorbidity were investigated by hierarchical cluster analysis.

Results

CKD was among the most frequently observed conditions and it was rarely observed without any other co-occurring disease. CKD was significantly associated with hypertension, anemia, heart failure, atrial fibrillation, myocardial infarction and hip fracture. When stratifying by SPPB, CKD was also significantly associated with vision impairment in SPPB = 5–8 group, and hearing impairment in SPPB = 0–4 group. Cluster analysis individuated two main clusters, one including CKD, hypertension and sensory impairments, and the second including all other conditions. Stratifying by SPPB, CKD contribute to a cluster including diabetes, anemia, osteoporosis, hypertension and sensory impairments in the SPPB = 0–4 group. When defining CKD as eGFR< 45 or 30 ml/min/1.73 m², the strength of the association of CKD with hypertension, sensory impairments, osteoporosis, anemia and CHF increased together with CKD severity in pairs analysis. Severe CKD (eGFR< 30 ml/min/1.73 m²) contributed to a wide cluster including cardiovascular, respiratory and neurologic diseases, as well as osteoporosis, hip fracture and cancer.

Conclusions

CKD and its severity may contribute significantly to specific multimorbidity patterns, at least based on the cluster analysis. Physical performance as assessed by SPPB may be associated with not negligible changes in both co-occurring pairs and multimorbidity clusters.

Trial registration

The SCOPE study is registered at clinicaltrials.gov (NCT02691546).

Clinical Implications of Estimating Glomerular Filtration Rate with Three Different Equations Among Older People. Preliminary Results of the Project "Screening for Chronic Kidney Disease among Older People across Europe (SCOPE)"

We aimed at investigating to what extent CKD may be staged interchangeably by three different eGFR equations in older people, and evaluating the source of discrepancies among equations in a population of 2257 patients older than 75 years enrolled in a multicenter observational study. eGFR was calculated by CKD-EPI, BIS and FAS equations. Statistical analysis was carried out by Bland–Altman analysis. κ statistic was used to quantify the agreement between equations in classifying CKD stages. The impact of selected variables on the difference among equations was graphically explored. The average difference between BIS and FAS was −0.24 (95% limits of agreement (95%LA = −4.64–4.14) mL/min/1.73 m². The difference between CKD-EPI and BIS and between CKD-EPI and FAS was 8.97 (95%LA = −2.90–20.84) and 8.72 (95%LA = −2.11–19.56) mL/min/1.73 m², respectively. As regards CKD stage classification, κ value was 0.47 for both CKD-EPI vs. FAS and CKD-EPI vs. BIS, while BIS and FAS had similar classificatory properties (κ = 0.90). Muscle mass was found related to the difference between CKD-EPI and BIS (R² = 0.11) or FAS (R² = 0.14), but not to the difference between BIS and FAS. In conclusion, CKD-EPI and BIS/FAS equations are not interchangeable to assess eGFR among older people. Muscle mass may represent a relevant source of discrepancy among eGFR equations.

[Concordance between the equations "Chronic Kidney Disease Epidemiological Collaboration" and "Modification of Diet in Renal Disease" with the "Berlin Initiative Study" to estimate renal function in the elderly]

OBJECTIVE

Estimated glomerular filtration rate (eGFR) is calculated routinely using creatinine-based formulas, but their reliability in the elderly is limited. The aim of this study was to analyse the concordance between the BIS1 equation which is specific for the elderly, and the usual CKD-EPI and MDRD-IDMS in a large population over 70 years of age.

MATERIAL AND METHODS

Retrospective cross-sectional study in which the eGFR was calculated using BIS1, CKD-EPI and MDRD-IDMS equations based on gender, age, and creatinine data of 85,089 subjects (58.5% women, mean age 78 years [IQR 73-83]).The following statistics were carried out: Wilcoxon test, Bland-Altman graphic analysis, study of the concordance using the intraclass correlation coefficient (ICC), and comparison tables for the classification of CKD.

RESULTS

The median of the eGFRs using BIS1 was 58mL/min/1.73m² (IQR 48-70), using CKD-EPI was 68mL/min/1.73m² (IQR 53-84), and using MDRD it was 68mL/min/1.73m² (IQR 53-82). The concordance between BIS1 and CKD-EPI (intraclass correlation coefficient =0.87) was found to be acceptable. It was lower with MDRD (intraclass correlation coefficient =0.81). A mean difference of 8mL/min/1.73m² (SD 2.6-18) was found BIS1 vs. CKD-EPI, and 10mL/min/1.73m² (SD 6-27) with BIS1 vs. MDRD, which was maintained when stratifying by gender and age groups.

CONCLUSIONS

Despite the acceptable statistical agreement, the eGFR obtained with the BIS1 equation is not interchangeable with CKD-EPI or with MDRD-IDMS. The BIS1 equation gives lower values than CKD-EPI, and classifies patients into a higher level of CKD, mainly when the eGFR is above 30mL/min/1.73 m².

Performance of glomerular filtration rate estimating equations in a community-based sample of Blacks and Whites: the multiethnic study of atherosclerosis

Background

The Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations are recommended for glomerular filtration rate (GFR) estimation in the general population. They have not been evaluated in community-based populations, including Blacks at higher levels of GFR, but are commonly applied in such populations.

Methods

In an ancillary study of Multi-Ethnic Study of Atherosclerosis conducted at one site, we evaluated the performance of the CKD-EPI equations for creatinine (eGFRcr), cystatin C (eGFRcys) or the combination (eGFRcr-cys) compared with GFR measured as plasma clearance of iohexol.

Results

Among 294 participants, the mean age was 71 (SD 9) years, 47% were Black, 48% were women and the mean measured GFR (mGFR) was 72.6 (SD 18.8) mL/min/1.73 m2. The CKD-EPI equations overestimated mGFR with a larger median bias for eGFRcr and eGFRcr-cys than eGFRcys [-8.3 (95% confidence interval -9.7, -6.5), -7.8 (-9.2, -6.2) and -3.7 (-5.0, -1.8) mL/min/1.73 m2, respectively], with smaller bias for those with lower compared with higher eGFR and by race compared with sex.

Conclusion

The small differential bias of the CKD-EPI equation between races suggests that they can be used in Blacks as well as Whites in older community-based adults. The large differential bias in women versus men in all equations is in contrast to other studies and is unexplained. Further studies are required in multiracial and multiethnic community-based cohorts, taking into account differences in GFR measurement methods.

Diagnostic Performance of Creatinine-Based Equations for Estimating Glomerular Filtration Rate in Adults 65 Years and Older

Importance

Estimating glomerular filtration rate (GFR) is useful in many clinical conditions. However, very few studies have evaluated the performance of GFR-estimating equations in older adults at various degrees of kidney impairment.

Objective

To determine the performance of plasma-creatinine-based equations Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI), Lund-Malmö Revised, (LMR), full age spectrum (FAS), and Berlin Initiative Study (BIS) 1 in older adults across a broad spectrum of GFRs.

Design, Setting, and Participants

Single-center cross-sectional study performed in France including 2247 participants aged 65 to 90 years who underwent inulin GFR measurements from July 1, 2003, to July 30, 2017, for suspected or established renal dysfunction, for renal risk, before kidney donation, or after kidney transplant.

Main Outcomes and Measures

The main outcome measure was GRF measured by inulin clearance. Equation performance criteria considered bias (difference between estimated and measured GFR), precision (interquartile range of the median difference), and accuracy P30 (percentage of estimated GFRs lying between [measured GFR - 30% of measured GFR] and [measured GFR + 30% of measured GFR]).

Results

The mean (SD) age of the 2247 participants was 71.5 (5) years and 1192 (53.0%) were male. The difference in median (95% CI) bias was significant between CKD-EPI vs LMR (-4.0 [-4.0 to -3.5 mL/min/1.73 m2; P < .001]) and CKD-EPI vs FAS (-2.0 [-3.5 to -2.5] mL/min/1.73 m2, P < .001) but not significant between CKD-EPI vs BIS 1 (0.0 [-1.5 to 0.5], P = .07, Mood test). In patients aged 65 to 74 years with measured GFR<45 mL/min/1.73 m2, the difference in median P30 (95% CI) was not significant between CKD-EPI vs LMR (P = .08) and CKD-EPI vs FAS (P = .48) but significant vs BIS 1 (P = .004, McNemar test). In subjects 75 years and older, with measured GFR less than 45 mL/min/1.73 m2, LMR and BIS 1 were more accurate than CKD-EPI and FAS (P30 = 74.5 [70.0-79.5] and 73.0 [68.0-78.0] vs 69.0 [64.5-74.0] and 69.0 [65.5-72.0]). In all patients, despite small statistical differences, the performance of CKD-EPI equation was not clinically different from that of LMR, FAS, or BIS 1.

Conclusions and Relevance

In a referral group of patients 65 years and older who had GFR estimated using CDK-EPI, LMR, BIS 1, and FAS equations, a comparison with renal inulin clearance found that none of the equations had a superior diagnostic performance. Each had limitations regarding accuracy.

A comparison between 2017 FAS and 2012 CKD-EPI equations: a multi-center validation study in Chinese adult population

BACKGROUND

The recent guidelines recommend using the estimated glomerular filtration rate (eGFR) to evaluate renal function. There are two reported full-age-spectrum (FAS) equations in 2017, which are based on serum cystatin C concentrations with or without accompanying serum creatinine level (FAS_Cr-Cys or FAS_Cys). We compared the performance and assessed the applicability of the new FAS equation with the 2012 CKD-EPI (CKD-EPI_Cys and CKD-EPI_Cr-Cys) equation in Chinese subjects.

METHODS

A total of 1184 patients, mean aged 55.06 year who underwent ^99mTc-DTPA GFR measurements (rGFR) from four hospitals were enrolled. The bias (eGFR-rGFR), precision (interquartile range of difference [IQR]), and accuracy (the proportion of eGFR within 30% of rGFR [P30]) of eGFR and rGFR calculated by four equations were compared.

RESULTS

Generally, the equation based on the combination of Cys and Scr performed superior to that on the basis of Cys alone, either the CKD-EPI_Cr-Cys or the FAS_Cr-Cys. Detailedly, referred to rGFR (67.33 ml/min/1.73 m²), the CKD-EPI_Cys, CKD-EPI_Cr-Cys, FAS_Cys, and the FAS_Cr-Cys estimated GFR 56.46 ml/min/1.73 m², 62.79 ml/min/1.73 m², 56.45 ml/min/1.73 m², and 61.04 ml/min/1.73 m², gave ROC^AUC0.944, 0.954, 0.943, and 0.953, respectively. Another comparison as to bias, precision, P₃₀, and RMSE with FAS_Cr-Cys were - 2.87 ml/min/1.73 m², 19.01 ml/min/1.73 m², 74.16%, and 17.84 ml/min/1.73 m² showed that FAS_Cr-Cys performed approximately more accurate than other equations, as well as the diagnostic consistency of GFR staging. In the rGFR < 60 ml/min/1.73 m² subgroup, the FAS_Cr-Cys equation showed the best performance. In older subjects, compared with FAS_Cys, CKD-EPI_Cr-Cys, and CKD-EPI_Cys, the FAS_Cr-Cys equation had relatively less bias (- 8.09 vs. - 9.63, - 7.52, - 11.04, P < 0.05), most precise (15.18 vs. 16.32, 15.22, 16.63), and most accuracy, P₃₀ was statistically different from the other equations, and achieved a ideal value > 70%.

CONCLUSION

The performance of the FAS_Cr-Cys equation is better than that of the CKD-EPI_Cr-Cys equation in the Chinese population, particularly in the elderly. Yet, further modification of FAS equations from a large-scale study could be more suitable for the Chinese population, particularly in older people.

Estimated glomerular filtration rate and functional status among older people: A systematic review

BACKGROUND

The association between chronic kidney disease (CKD) and functional status may change as a function of the equation used to estimate glomerular filtration rate (eGFR). We reviewed the predictive value of different eGFR equations in regard to frailty and disability outcomes.

METHODS

We searched Pubmed from inception to March 2018 for studies investigating the association between eGFR and self-reported and/or objective measures of frailty or disability. Cross-sectional and longitudinal studies were separately analysed.

RESULTS

We included 16 studies, one of which reporting both cross-sectional and longitudinal data. Three out of 7 cross-sectional studies compared different eGFR equations in regard to their association with functional status: two studies showed that cystatin C-based, but not creatinine-based eGFR may be associated with hand-grip strength or frailty; another study showed that two different creatinine-based eGFR equations may be similarly associated with disability. Four out of 10 longitudinal studies provided comparative data: two studies reported similar association with disability for different creatinine-based eGFR equations; one study showed that creatinine-based eGFR was not associated with frailty, but a not significant trend for association was observed with cystatin C-based eGFR; one study showed that cystatin C-based but not creatinine-based eGFR may predict incident mobility disability, while both methods may predict gait speed decline. High heterogeneity was observed in regard to confounders included in reviewed studies. None of them included the most recently published equations.

CONCLUSION

Available data do not support the superiority of one of the eGFR equations in terms of measuring or predicting functional decline.

Comparison of glomerular filtration rate estimating equations derived from creatinine and cystatin C: validation in the Age, Gene/Environment Susceptibility-Reykjavik elderly cohort

Background

Validation studies comparing glomerular filtration rate (GFR) equations based on standardized creatinine and cystatin C assays in the elderly are needed. The Icelandic Age, Gene/Environment Susceptibility-Kidney cohort was used to compare two pairs of recently developed GFR equations, the revised Lund-Malmö creatinine equation (LMRCr) and the arithmetic mean of the LMRCr and Caucasian, Asian, Paediatric and Adult cystatin C equations (MEANLMR+CAPA), as well as the Full Age Spectrum creatinine equation (FASCr) and its combination with cystatin C (FASCr+Cys), with the corresponding pair of Chronic Kidney Disease Epidemiology Collaboration equations (CKD-EPICr and CKD-EPICr+Cys).

Methods

A total of 805 individuals, 74-93 years of age, underwent measurement of GFR (mGFR) using plasma clearance of iohexol. Four metrics were used to compare the performance of the GFR equations: bias, precision, accuracy [including the percentage of participants with estimated GFR (eGFR) within 30% of mGFR (P30)] and the ability to detect mGFR <60 mL/min/1.73 m2.

Results

All equations had a P30 >90%. LMRCr and FASCr yielded significantly higher precision and P30 than CKD-EPICr, while bias was significantly worse. LMRCr, FASCr and CKD-EPICr showed similar ability to detect mGFR <60 mL/min/1.73 m2 based on the area under the receiver operating characteristic curves. MEANLMR+CAPA, FASCr+Cys and CKD-EPICr+Cys all exhibited consistent improvements compared with the corresponding creatinine-based equations.

Conclusion

None of the creatinine-based equations was clearly superior overall in this community-dwelling elderly cohort. The addition of cystatin C improved all of the creatinine-based equations.

Drug-Induced Kidney Injury in the Elderly

The incidence of acute kidney injury in the elderly has grown over the past decade. One of the primary drivers is drug-induced nephrotoxicity, which is the result of a combination of the unique susceptibilities to kidney injury and the increased use of medications in the elderly population. Specific drug classes are associated with increased rates of kidney injury including agents that block the renin angiotensin system, antimicrobials, and chemotherapeutic agents. Mechanistically, injury may be due to hemodynamic effects, tubular or glomerular toxicity, and interstitial nephritis. Early recognition of nephrotoxicity is critical, as are preventative steps when applicable. Unfortunately, treatment for established drug-induced kidney injury is limited and supportive care is required. Limiting exposure to nephrotoxic drugs is critical in decreasing the incidence of acute kidney injury in the elderly patient.

Prevalence and determinants of differences in cystatin C and creatinine-based estimated glomerular filtration rate in community-dwelling older adults: a cross-sectional study

Background

Differences in cystatin C and creatinine-based estimated glomerular filtration rate (eGFR) can lead to clinical uncertainty. Existing eGFR equations perform poorly in a subset of individuals. This study aims to describe the prevalence of differences between cystatin C-based (eGFR_cys) and creatinine-based (eGFR_creat) eGFR in older adults and to explore which subsets of individuals may be most affected by differing estimations.

Methods

In this cross-sectional study, participants from a cohort of community-dwelling older adults were examined at a baseline visit in 2001-2004 as part of the larger “Good Aging in Skåne” study. Exposure variables were obtained from questionnaires, interviews, examinations, and medical records. Blood samples were taken during the baseline visit, cryopreserved, and analyzed at a later time for biomarkers. The CKD-EPI equations were used to estimate GFR. Initial descriptive analyses were performed on 2931 individuals. A total of 2532 participants were included in the final multiple linear regression.

Results

Nearly two-thirds of participants had eGFR differences exceeding 10%, with nearly 20 % of participants having eGFR differences exceeding 30%. Smoking, age, body mass index (BMI), C-reactive protein (CRP), glucocorticoid use, and mean eGFR were correlated with differences between eGFR_creat and eGFR_cys.

Conclusions

Differences between eGFR_creat and eGFR_cys are common and often of large magnitude in this community-dwelling population of older adults. The finding of multiple non-GFR determinants correlated to differences in GFR estimations can help direct future research to improve eGFR equations for subgroups prone to conflicting GFR estimations or to guide choice of biomarker for GFR estimation in these subgroups.

Electronic supplementary material

The online version of this article (10.1186/s12882-017-0759-3) contains supplementary material, which is available to authorized users.

Prognostic usefulness of an age-adapted equation for renal function assessment in older patients with acute coronary syndrome

BACKGROUND:

Renal dysfunction negatively impacts survival in acute coronary syndrome patients. The Berlin Initiative Study creatinine-based (BIS_crea) equation has recently been proposed for renal function assessment in older persons. However, up to now it is unknown if the superiority of the new BIS_crea equation, with respect to the most recommended chronic kidney disease epidemiology collaboration creatinine-based (CKD-EPI_crea) formula, would translate into better risk prediction of adverse events in older patients with acute coronary syndrome.

OBJECTIVES:

To study the impact of using estimated glomerular filtration rate calculated according to the BIS_crea and CKD-EPI_crea equations on mortality in acute coronary syndrome patients aged 70 years and over.

METHODS:

Retrospectively, between 2011 and 2016, a total of 2008 patients with acute coronary syndrome (64% men; age 79±7 years) were studied. Follow-up was 18±10 months. Measures of performance were evaluated using continuous data and stratifying patients into three estimated glomerular filtration rate subgroups: ≥60, 59.9-30 and <30 mL/min/1.73 m².

RESULTS:

The two formulas afforded independent prognostic information over follow-up. However, risk prediction was most accurate using the BIS_crea formula as evaluated by Cox proportional hazards models (hazard ratio (for each 10 mL/min/1.73 m² decrease) 1.47 vs. 1.27 with the CKD-EPI equation; P<0.001 for comparison), c-statistic values (0.69 vs. 0.65, respectively; P=0.04 for comparison) and Bayesian information criterion. Net reclassification improvement based on the estimated glomerular filtration rate categories significantly favoured BIS_crea +9 (95% confidence interval 2-16%; P=0.02).

CONCLUSIONS:

Our findings suggest that the BIS_crea formula may improve death risk prediction more than the CKD-EPI_crea formula in older patients with acute coronary syndrome.

Estimating renal function in old people: an in-depth review

Estimates of glomerular filtration rate (eGFR) should provide accurate measure of an individual's kidney function because important clinical decisions such as timing of renal replacement therapy and drug dosing may be dependent on eGFR. Formulae from which eGFR is derived are generally based on serum creatinine measurement, such as Cockcroft-Gault, MDRD and CKD-EPI. More recently, calculation of eGFR using other laboratory biomarkers such as cystatin C has emerged with apparent greater accuracy. In old people, there is age-related physiological change in the kidney, which could lead to reduced GFR. Likewise, physiological changes in body composition that occur with the ageing process impede the use of a single creatinine-based calculation of eGFR across all adult age groups. Studies have shown differences in the prevalence of CKD based on the type of equation used to estimate GFR. This review discusses the evolution of eGFR calculations and the relative accuracy of such equations in older population.

Renal Function and Death in Older Women: Which eGFR Formula Should We Use?

Background. The Berlin Initiative Study (BIS) eGFR equations were developed specifically for aged populations, but their predictive validity compared to standard formulae is unknown in older women. Methods. In a prospective study of 1289 community-dwelling older women (mean age 79.5 years), we compared the performance of the BIS1 SCr-based equation to the CKD-EPIcr and the BIS2 SCr- and Scysc-based equation to the CKD-EPIcr,cysc to predict cardiovascular and all-cause mortality. Results. Prevalence of specific eGFR category (i.e., ≥75, 60-74, 45-59, and <45) according to eGFR equation was 12.3%, 38.4%, 37.3%, and 12.0% for BIS1; 48.3%, 27.8%, 16.2%, and 7.8% for CKD-EPIcr; 14.1%, 38.6%, 37.6%, and 9.6% for BIS2; and 33.5%, 33.4%, 22.0%, and 11.1% for CKD-EPIcr,cysc, respectively. Over 9 ± 4 years, 667 (51.8%) women died. For each equation, women with eGFR <45 were at increased risk of mortality compared to eGFR ≥75 [adjusted HR (95% CI): BIS1, 1.5 (1.1-2.0); CKD-EPIcr, 1.7 (1.3-2.2); BIS2, 2.0 (1.4-2.8); CKD-EPIcr,cysc, 1.8 (1.4-2.3); p-trend <0.01]. Net reclassification analyses found no material difference in discriminant ability between the BIS and CKD-EPI equations. Results were similar for cardiovascular death. Conclusions. Compared to CKD-EPI, BIS equations identified a greater proportion of older women as having CKD but performed similarly to predict mortality risk. Thus, the BIS equations should not replace CKD-EPI equations to predict risk of death in older women.

Agreement between Chronic Kidney Disease Epidemiological Collaboration and Berlin Initiative Study equations for estimating glomerular filtration rate in older people: The Invecchiare in Chianti (Aging in Chianti Region) study

AIM

The aim was to investigate to what extent chronic kidney disease (CKD) can be staged interchangeably by Chronic Kidney Disease Epidemiological Collaboration (CKD-EPI) and by Berlin Initiative Study (BIS) equations, and to verify whether cystatin C can improve concordance between formulas.

METHODS

Our series consisted of 828 community-dwelling individuals aged 65 years or older enrolled in the Invecchiare in Chianti Study ("Aging in the Chianti Region"). Estimated glomerular filtration rate was calculated using the creatinine-based CKD-EPI, creatinine/cystatin C-based CKD-EPI, creatinine-based BIS and creatinine/cystatin C-based BIS equations. Agreement and sources of discrepancy between equations in identifying people with different degrees of kidney dysfunction was investigated by κ statistic and Bland-Altman plots.

RESULTS

Overall, CKD-EPI values were higher than that obtained with BIS equations, especially for eGFR = 30-60 mL/min/1.73 m² . A total of 191 out of 828 participants were classified in stage 2 by the creatinine-based CKD-EPI and in stage 3a by the creatinine-based BIS equation, whereas 123 participants were classified in stage 2 by creatinine/cystatin C-based CKD-EPI and in stage 3a by the creatinine/cystatin C-based BIS equation. A total of 27 participants were classified in stage 3a by creatinine-based CKD-EPI and in stage 3b by creatinine-based BIS equation, whereas 18 were classified as stage 3a by creatinine/cystatin C-based CKD-EPI and stage 3b by the creatinine/cystatin C-based BIS equation.

CONCLUSIONS

Despite a fair overall concordance, the CKD-EPI and BIS equations cannot be considered interchangeable to assess estimated glomerular filtration rate in older people, and using creatinine/cystatin C-based rather than creatinine-based equations only marginally improves the concordance between CKD-EPI and BIS. Disagreement between equations might significantly impact the applications of stage-specific measures for managing CKD among older people. Geriatr Gerontol Int 2017; 17: 1559-1567.

Chronic kidney disease: towards a risk-based approach

Chronic kidney disease (CKD) affects 8-16% of adults worldwide and is associated with multiple adverse outcomes. It includes a heterogeneous group of conditions with widely varied associated risks; risk stratification is therefore vital for clinical management. Use of the CKD Epidemiology Collaboration (CKD-EPI) equation to estimate glomerular filtration rate (GFR) instead of the Modification of Diet in Renal Disease (MDRD) equation will reduce, though not eliminate, over-diagnosis of CKD. Cystatin C is recommended as an alternative measure of GFR but is not yet widely used. A new classification system for CKD, which includes GFR and albuminuria, has been endorsed by the National Institute for Health and Care Excellence to aid risk stratification and a recently validated formula, requiring only age, gender, eGFR and albuminuria, is useful to predict risk of end-stage kidney disease (ESKD). A risk-based approach will facilitate appropriate treatment for people at high risk of developing ESKD while sparing the majority, who are at low risk, from unnecessary intervention.

Estimated GFR and Mortality in Older Men: Are All eGFR Formulae Equal

BACKGROUND

Recently, the first estimated glomerular filtration rate (eGFR) formula specifically developed for community-dwelling older adults, the Berlin Initiative Study Equation 2 (BIS2), was reported. To date, however, no study has examined the performance of the BIS2 to predict death in older adults as compared to equations used clinically and in research.

METHODS

We prospectively followed 2,994 community-dwelling men (age 76.4 ± 5.6) enrolled in the MrOS Sleep Study. We calculated baseline eGFR from serum creatinine and cystatin-C using the BIS2, Chronic Kidney Disease Epidemiology (CKD-EPIcr,cysc), CKD-EPIcysc and CKD-EPIcr equations. Analyses included Cox-proportional hazards regression and net reclassification improvement (NRI) for the outcomes of all-cause and cardiovascular death.

RESULTS

Follow-up time was 7.3 ± 1.9 years. By BIS2, 42 and 11% had eGFR <60 and <45, respectively, compared to CKD-EPIcr (23 and 6%), CKD-EPIcysc (36 and 13%) and CKD-EPIcr,cysc (28 and 8%). BIS2 eGFR <45 was associated with twofold higher rate of all-cause mortality when compared to eGFR ≥75 after multivariate adjustment (HR 2.1, 95% CI 1.5-2.8). Results were similar for CKD-EPIcr,cysc <45 (HR 2.1, 95% CI 1.6-2.7) and CKD-EPIcysc <45 (HR 2.1, 95% CI 1.7-2.7) and weaker for CKD-EPIcr <45 (HR 1.5, 95% CI 1.2-2.0). In NRI analyses, when compared to CKD-EPIcr,cysc, both BIS2 and CKD-EPIcr equations more often misclassified participants with respect to mortality. We found similar results for cardiovascular death.

CONCLUSION

The BIS2 did not outperform and the CKD-EPIcr was inferior to the cystatin C-based CKD-EPI equations to predict death in this cohort of older men. Thus, the cystatin C-based CKD-EPI equations are the formulae of choice to predict death in community-dwelling older men.

Performance of the creatinine and cystatin C-based equations for estimation of GFR in Chinese patients with chronic kidney disease

BACKGROUND

Currently, creatinine- or cystatin C-based glomerular filtration rate (GFR) estimation equation has been recommended to assess GFR in CKD patients. However, it is still obscure whether those equations performed consistently outstandingly in Chinese population.

METHODS

The equations were validated in a population totaling 632 participants (mean age 61.6 ± 12.3 years). The estimated GFR (eGFR) calculated separately by six equations (C-MDRD, C_cys, C_scr-cys, CKD-EPI_scr, CKD-EPI_cys, and CKD-EPI_scr-cys equations) was compared with the reference GFR (rGFR) measured by the ^99mTc-DTPA renal dynamic imaging method. Participants were divided into age and rGFR specific subgroups.

RESULTS

CKD-EPI_scr-cys equation had a larger area under receiver operating characteristic curve (ROC^AUC) and relative higher sensitivity (79.8 %) and specificity (93 %) to diagnose CKD. CKD-EPI_scr-cys and CKD-EPI_cys equations appeared to be more accurate with higher proportion of eGFR within 30 % of rGFR (P ₃₀) value. Those two equations performed as well in older people as in the younger population. The CKD-EPI_scr-cys equation acquired the highest P ₃₀ (80.9 %) in subgroups with rGFR ≥60 mL/min/1.73 m², while the CKD-EPI_cys equation yielded the best performance in the rGFR <60 mL/min/1.73 m² subgroup.

CONCLUSION

CKD-EPI_scr-cys formula had better capability to accurately evaluate GFR in the participants CKD stages 1-2 in Chinese ethnic. The application of the cystatin C-based equations may be the optimal one for patients of moderately to severely injured GFR. Considering the accuracy in the entire range of participants less ideally, the additional of the Chinese racial factor is assumed to be essential.

Chronic kidney disease and prognosis in elderly patients with cardiovascular disease: Comparison between CKD-EPI and Berlin Initiative Study-1 formulas

BACKGROUND

Chronic kidney disease (CKD) is frequent in patients with cardiovascular (CV) disease and impacts prognosis in these subjects. While current guidelines recommend the CKD-EPI equation for the estimated glomerular filtration rate (eGFR) and recognizing CKD, a new creatinine-based equation - the Berlin Initiative Study-1 (BIS-1) - was generated for elders with a high prevalence of CV disease. We assessed whether BIS-1 provided more accurate risk stratification than the CKD-EPI equation in unselected aged patients with CV disease.

METHODS

Patients aged ≥70 years who were seen consecutively at the Cardiovascular Centre of Trieste (Italy) between November 2009 and October 2013 were recruited into this study. The correlation and agreement between the BIS-1 and CKD-EPI formulas were evaluated and intra-class correlation coefficients (ICCs) were computed in order to estimate the correlation between the two formulas. Patients were followed for all-cause death, composite outcomes of all-cause death/all-cause hospitalization and all-cause death/CV hospitalization.

RESULTS

A total of 7845 subjects met the inclusion criteria for this study. GFR as estimated with the BIS-1 and the CKD-EPI equation was highly correlated (ICC: 0.81; 95% confidence interval [CI]: 0.79-0.82; p < 0.0001). When allocating patients in Kidney Disease Improving Global Outcomes classes of eGFR, compared to CKD-EPI, the BIS-1 formula reclassified 2720 (34.7%) patients: 53 (1.9%) were placed in a better class and 2667 (98.1%) were placed in a worse class. Multivariable Cox models showed that BIS-1 compared to CKD-EPI had a significantly better accuracy for predicting death (NRI: 0.12; 95% CI: 0.03-0.19; p = 0.001), death/CV hospitalization (net reclassification improvement [NRI]: 0.34; 95% CI: 0.27-0.38; p < 0.001) and death/all-cause hospitalization (NRI: 0.14; 95% CI: 0.06-0.21; p = 0.001).

CONCLUSIONS

The BIS-1 formula is better than the CKD-EPI formula for risk stratification of CKD in elderly people with CV disease.

An estimated glomerular filtration rate equation for the full age spectrum

BACKGROUND

Glomerular filtration rate (GFR) is accepted as the best indicator of kidney function and is commonly estimated from serum creatinine (SCr)-based equations. Separate equations have been developed for children (Schwartz equation), younger and middle-age adults [Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation] and older adults [Berlin Initiative Study 1 (BIS1) equation], and these equations lack continuity with ageing. We developed and validated an equation for estimating the glomerular filtration rate that can be used across the full age spectrum (FAS).

METHODS

The new FAS equation is based on normalized serum creatinine (SCr/Q), where Q is the median SCr from healthy populations to account for age and sex. Coefficients for the equation are mathematically obtained by requiring continuity during the paediatric-adult and adult-elderly transition. Research studies containing a total of 6870 healthy and kidney-diseased white individuals, including 735 children, <18 years of age, 4371 adults, between 18 and 70 years of age, and 1764 older adults, ≥70 years of age with measured GFR (inulin, iohexol and iothalamate clearance) and isotope dilution mass spectrometry-equivalent SCr, were used for the validation. Bias, precision and accuracy (P30) were evaluated.

RESULTS

The FAS equation was less biased [-1.7 (95% CI -3.4, -0.2) versus 6.0 (4.5, 7.5)] and more accurate [87.5% (85.1, 89.9) versus 83.8% (81.1, 86.5)] than the Schwartz equation for children and adolescents; less biased [5.0 (4.5, 5.5) versus 6.3 (5.9, 6.8)] and as accurate [81.6% (80.4, 82.7) versus 81.9% (80.7, 83.0)] as the CKD-EPI equation for young and middle-age adults; and less biased [-1.1 (-1.6, -0.6) versus 5.6 (5.1, 6.2)] and more accurate [86.1% (84.4, 87.7) versus 81.8% (79.7, 84.0)] than CKD-EPI for older adults.

CONCLUSIONS

The FAS equation has improved validity and continuity across the full age-spectrum and overcomes the problem of implausible eGFR changes in patients which would otherwise occur when switching between more age-specific equations.

Epidemiology and Public Health Concerns of CKD in Older Adults

CKD is increasingly common in older adults. Estimating the glomerular filtration rate can be challenging in this population, with sarcopenia affecting the accuracy of various formulae. Competing risks of death influence the risk of progression to end-stage kidney disease. In managing CKD in this population, one must take into consideration other comorbidities including assessment of geriatric syndromes. More research is still needed to guide medical management in this heterogeneous population.

[Dosing adjustment and renal function: Which equation(s)?]

While the CKD-EPI (for Chronic Kidney Disease Epidemiology) equation is now implemented worldwide, utilization of the Cockcroft formula is still advocated by some physicians for drug dosage adjustment. Justifications for this recommendation are that the Cockcroft formula was preferentially used to determine dose adjustments according to renal function during the development of many drugs, better predicts drugs-related adverse events and decreases the risk of drug overexposure in the elderly. In this opinion paper, we discuss the weaknesses of the rationale supporting the Cockcroft formula and endorse the French HAS (Haute Autorité de santé) recommendation regarding the preferential use of the CKD-EPI equation. When glomerular filtration rate (GFR) is estimated in order to adjust drug dosage, the CKD-EPI value should be re-expressed for the individual body surface area (BSA). Given the difficulty to accurately estimate GFR in the elderly and in individuals with extra-normal BSA, we recommend to prescribe in priority monitorable drugs in those populations or to determine their "true" GFR using a direct measurement method.

Prediction of mortality using quantification of renal function in acute heart failure

BACKGROUND

Renal function, as quantified by the estimated glomerular filtration rate (eGFR), is a predictor of death in acute heart failure (AHF). It is unknown whether one of the clinically-available serum creatinine-based formulas to calculate eGFR is superior to the others for predicting mortality.

METHODS AND RESULTS

We quantified renal function using five different formulas (Cockroft-Gault, MDRD-4, MDRD-6, CKD-EPI in patients<70 years, and BIS-1 in patients≥70 years) in 1104 unselected AHF patients presenting to the emergency department and enrolled in a multicenter study. Two independent cardiologists adjudicated the diagnosis of AHF. The primary endpoint was the accuracy of the five eGFR equations to predict death as quantified by the time-dependent area under the receiver-operating characteristics curve (AUC). The secondary endpoint was the accuracy to predict all-cause readmissions and readmissions due to AHF. In a median follow-up of 374 days (IQR: 221 to 687 days), 445 patients (40.3%) died. eGFR as calculated by all equations was an independent predictor of mortality. The Cockcroft-Gault formula showed the highest prognostic accuracy (AUC 0.70 versus 0.65 for MDRD-4, 0.55 for MDRD-6, and 0.67 for the combined formula CKD-EPI/BIS-1, p<0.05). These findings were confirmed in patients with varying degrees of renal function and in three vulnerable subgroups: women, patients with severe left ventricular dysfunction, and the elderly. The prognostic accuracy for readmission was poor for all equations, with an AUC around 0.5.

CONCLUSIONS

Calculating eGFR using the Cockcroft-Gault formula assesses the risk of mortality in patients with AHF more accurately than other commonly used formulas.

Evaluation of renal function in the elderly, not as easy as it seems: a review

In the elderly assessment of renal function by glomerular filtration rate estimation is crucial for diagnostic, therapeutic and prognostic purposes. Our aim is to illustrate the different formulas available and their respective advantages and disadvantages.

Iohexol plasma clearance measurement in older adults with chronic kidney disease-sampling time matters

BACKGROUND

Accurate and precise measurement of GFR is important for patients with chronic kidney disease (CKD). Sampling time of exogenous filtration markers may have great impact on measured GFR (mGFR) results, but there is still uncertainty about optimal timing of plasma clearance measurement in patients with advanced CKD, for whom 24-h measurement is recommended. This satellite project of the Berlin Initiative Study evaluates whether 24-h iohexol plasma clearance reveals a clinically relevant difference compared with 5-h measurement in older adults.

METHODS

In 104 participants with a mean age of 79 years and diagnosed CKD, we performed standard GFR measurement over 5 h (mGFR300) using iohexol plasma concentrations at 120, 180, 240 and 300 min after injection. With an additional sample at 1440 min, we assessed 24-h GFR measurement (mGFR1440). Study design was cross-sectional. Calculation of mGFR was conducted with a one compartment model using the Brochner-Mortensen equation to calculate the fast component. mGFR values were compared with estimated GFR values (MDRD, CKD-EPI, BIS1, Revised Lund-Malmö and Cockcroft-Gault).

RESULTS

In all 104 subjects, mGFR1440 was lower than mGFR300 (23 ± 8 versus 29 ± 9 mL/min/1.73 m(2), mean ± SD; P < 0.001). mGFR1440 was highly correlated with mGFR300 (r = 0.9). The mean absolute difference mGFR300 - mGFR1440 was 5.9 mL/min/1.73 m(2) corresponding to a mean percentage difference of 29%. In individuals with eGFRCKD-EPI ≤ 30 mL/min/1.73 m(2), percentage difference of mGFR300 and mGFR1440 was even higher (35%). To predict mGFR1440 from mGFR300, we developed the correction formula: mGFR1440 = -2.175 + 0.871 × mGFR300 (1-fold standard error of estimate: ±2.3 mL/min/1.73 m(2)). The GFR estimating equation with the best accuracy and precision compared with mGFR300 and mGFR1440 was the Revised Lund Malmö.

CONCLUSIONS

In elderly CKD patients, measurement of iohexol clearance up to 5 h leads to a clinically relevant overestimation of GFR compared with 24-h measurement. In clinical care, this effect should be bore in mind especially for patients with considerably reduced GFR levels. A new correction formula has been developed to predict mGFR1440 from mGFR300. For accurate GFR estimates in elderly CKD patients, we recommend the Revised Lund Malmö equation.

Comparing GFR Estimating Equations Using Cystatin C and Creatinine in Elderly Individuals

Current guidelines recommend reporting eGFR using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations unless other equations are more accurate, and recommend the combination of creatinine and cystatin C (eGFRcr-cys) as more accurate than either eGFRcr or eGFRcys alone. However, preferred equations and filtration markers in elderly individuals are debated. In 805 adults enrolled in the community-based Age, Gene/Environment Susceptibility (AGES)-Reykjavik Study, we measured GFR (mGFR) using plasma clearance of iohexol, standardized creatinine and cystatin C, and eGFR using the CKD-EPI, Japanese, Berlin Initiative Study (BIS), and Caucasian and Asian pediatric and adult subjects (CAPA) equations. We evaluated equation performance using bias, precision, and two measures of accuracy. We first compared the Japanese, BIS, and CAPA equations with the CKD-EPI equations to determine the preferred equations, and then compared eGFRcr and eGFRcys with eGFRcr-cys using the preferred equations. Mean (SD) age was 80.3 (4.0) years. Median (25th, 75th) mGFR was 64 (52, 73) ml/min per 1.73 m(2), and the prevalence of decreased GFR was 39% (95% confidence interval, 35.8 to 42.5). Among 24 comparisons with the other equations, CKD-EPI equations performed better in 9, similar in 13, and worse in 2. Using the CKD-EPI equations, eGFRcr-cys performed better than eGFRcr in four metrics, better than eGFRcys in two metrics, and similar to eGFRcys in two metrics. In conclusion, neither the Japanese, BIS, nor CAPA equations were superior to the CKD-EPI equations in this cohort of community-dwelling elderly individuals. Using the CKD-EPI equations, eGFRcr-cys performed better than eGFRcr or eGFRcys.