Prediction of glomerular filtration rate from serum creatinine concentration in advanced chronic renal failure

Kidney function estimation equations: a narrative review

Glomerular filtration rate (GFR) as a marker of kidney function is important in health and disease management because decreased kidney function is associated with all-cause and cardiovascular mortality, progression of kidney disease, predisposition to acute kidney injury (AKI), and for drug dosage modification. While measured glomerular filtration rate (mGFR) is acknowledged as the most accurate method for evaluating kidney function, it is at present not feasible to be applied in the clinical arena. Estimated glomerular filtration rate (eGFR) is preferred due to its convenience, cost-effectiveness, and seamless integration into standard clinical practice for kidney function evaluation. The presence of multiple equations for eGFR with applications to differing populations makes their use challenging for clinicians. We reviewed available estimated glomerular filtration rate (GFR) equations and their application in different clinical settings both in normal and chronic kidney disease (CKD) patients. These formulae incorporate serum creatinine and/or serum cystatin C levels and correlate them with measured kidney function. Among the many available equations, the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equation is the most recommended due to its robustness and accuracy across diverse patient populations. Strengths and limitations of different eGFR equations are discussed emphasizing the importance of selecting the appropriate equation based on specific patient demographics and clinical scenarios. There is need for regional validation studies to ensure the global applicability of these equations, considering the variations in population characteristics.

Living donors kidney transplantation and oxidative stress: Nitric oxide as a predictive marker of graft function

BACKGROUND

Glomerular filtration rate is the best indicator of renal function and a predictor of graft and patient survival after kidney transplantation.

METHODS

In a single-centre prospective analysis, we assessed the predictive performances of 4 oxidative stress biomarkers in estimating graft function at 6 months and 1 year after kidney transplantation from living donors. Blood samples were achieved on days (D-1, D1, D2, D3, D6 and D8), months (M1, M3 and M6) and after one year (1Y). For donors, a blood sample was collected on D-1. Malondialdehyde (MDA), nitric oxide (NO), glutathione s-transferase (GST), myeloperoxydase (MPO), and creatinine (Cr) were measured by spectrophotometric essays. The estimated glomerular filtration rate by the modification of diet in renal disease equation (MDRD-eGFR) was used to assess renal function in 32 consecutive donor-recipient pairs. Pearson's and Spearman's correlations have been applied to filter out variables and covariables that can be used to build predictive models of graft function at six months and one year. The predictive performances of NO and MPO were tested by multivariable stepwise linear regression to estimate glomerular filtration rate at six months.

RESULTS

Three models with the highest coefficients of determination stand out, combining the two variables nitric oxide at day 6 and an MDRD-eGFR variable at day 6 or MDRD-eGFR at day 21 or MDRD-eGFR at 3 months, associated for the first two models or not for the third model with donor age as a covariable (P = 0.000, r2 = 0.599, r2adj = 0.549; P = 0.000, r2 = 0.548, r2adj = 0.497; P = 0.000, r2 = 0.553, r2adj = 0.517 respectively).

CONCLUSION

Quantification of nitric oxide at day six could be useful in predicting graft function at six months in association with donor age and the estimated glomerular filtration rate in recipient at day 6, day 21 and 3 months after transplantation.

Utilizing Estimated Creatinine Excretion to Improve the Performance of Spot Urine Samples for the Determination of Proteinuria in Kidney Transplant Recipients

BACKGROUND

Agreement between spot and 24-hour urine protein measurements is poor in kidney transplant recipients. We investigated whether using formulae to estimate creatinine excretion rate (eCER), rather than assuming a standard creatinine excretion rate, would improve the estimation of proteinuria from spot urine samples in kidney transplant recipients.

METHODS

We measured 24 hour urine protein and albumin and spot albumin:creatinine (ACR) and spot protein:creatinine (PCR) in 181 Kidney transplant recipients." We utilized 6 different published formulae (Fotheringham, CKD-EPI, Cockcroft-Gault, Walser, Goldwasser and Rule) to estimate eCER and from it calculated estimated albumin and protein excretion rate (eAER and ePER). Bias, precision and accuracy (within 15%, 30% and 50%) of ACR, PCR, eAER, ePER were compared to 24-hour urine protein and albumin.

RESULTS

ACR and PCR significantly underestimated 24-hour albumin and protein excretion (ACR Bias (IQR), -5.9 mg/day; p< 0.01; PCR Bias, (IQR), -35.2 mg/day; p<0.01). None of the formulae used to calculate eAER or ePER had a bias that was significantly different from the 24-hour collection (eAER and ePER bias: Fotheringham -0.3 and 7.2, CKD-EPI 0.3 and 13.5, Cockcroft-Gault -3.2 and -13.9, Walser -1.7 and 3.1, Goldwasser -1.3 and -0.5, Rule -0.6 and 4.2 mg/day respectively. The accuracy for ACR and PCR were lower (within 30% being 38% and 43% respectively) than the corresponding values estimated by utilizing eCER (for eAER 46% to 49% and ePER 46-54%).

CONCLUSION

Utilizing estimated creatinine excretion to calculate eAER and ePER improves the estimation of 24-hour albuminuria/proteinuria with spot urine samples in kidney transplant recipients.

Glomerular filtration rate equations: a comprehensive review

Since evaluation of glomerular filtration rate (GFR) is very important in daily medical care, and reliable methods for measuring GFR are too complicated, there has been along decades an enormous effort for developing accurate GFR equations. In the present review article, we performed a comprehensive analysis of the mainly described GFR equations, and we concluded that although MDRD, CKD-EPI, DRA and Gregori-Macías equations are valid to monitor renal function as well as to stage and follow up renal patients, the clinical nephrological evaluation still remains the best alternative for diagnosing renal health and disease.

Estimating glomerular filtration rate in kidney transplantation: Still searching for the best marker

Kidney transplantation is the treatment of choice for end-stage renal disease. The evaluation of graft function is mandatory in the management of renal transplant recipients. Glomerular filtration rate (GFR), is generally considered the best index of graft function and also a predictor of graft and patient survival. However GFR measurement using inulin clearance, the gold standard for its measurement and exogenous markers such as radiolabeled isotopes ((51)Cr EDTA, (99m)Tc DTPA or (125)I Iothalamate) and non-radioactive contrast agents (Iothalamate or Iohexol), is laborious as well as expensive, being rarely used in clinical practice. Therefore, endogenous markers, such as serum creatinine or cystatin C, are used to estimate kidney function, and equations using these markers adjusted to other variables, mainly demographic, are an attempt to improve accuracy in estimation of GFR (eGFR). Nevertheless, there is some concern about the inability of the available eGFR equations to accurately identify changes in GFR, in kidney transplant recipients. This article will review and discuss the performance and limitations of these endogenous markers and their equations as estimators of GFR in the kidney transplant recipients, and their ability in predicting significant clinical outcomes.

Diffusion-weighted MRI with parallel imaging technique: apparent diffusion coefficient determination in normal kidneys and in nonmalignant renal diseases

The purpose of the study was to assess the capability and the reliability of apparent diffusion coefficient (ADC) measurements in the evaluation of different benign renal abnormalities. Twenty-five healthy volunteers and 31 patients, divided into seven different groups (A-G) according to pathology, underwent diffusion-weighted magnetic resonance imaging (DW MRI) of the kidneys using 1.5-T system. DW images were obtained in the axial plane with a spin-echo echo planar imaging single-shot sequence with three b values (0, 300, and 600 s/mm²). Before acquisition of DW sequences, we performed in each patient a morphological study of the kidneys. ADC was 2.40±0.20×10⁻³ mm² s⁻¹ in volunteers. A significant difference was found between Groups A (cysts=3.39±0.51×10⁻³ mm² s⁻¹) and B (acute/chronic renal failure=1.38±0.40×10⁻³ mm² s⁻¹) and between Groups A and C (chronic pyelonephritis=1.53±0.21×10⁻³ mm² s⁻¹) (P<.05). An important difference was also observed among Group D (hydronephrosis=4.82±0.35×10⁻³ mm² s⁻¹) and Groups A, B, and C (P<.05), whereas no differences were found between Groups B and C (P>.05). A considerable correlation between glomerular filtration rate and ADC was found (P=.04). In conclusion, significant differences were detected among different patient groups, and this suggests that ADC measurements can be useful in differentiating normal renal parenchyma from most commonly encountered nonmalignant renal lesions.

Effect of N-acetylcysteine on serum creatinine and kidney function: results of a randomized controlled trial

BACKGROUND

Evidence for a protective effect of N-acetylcysteine (NAC) on acute and chronic kidney disease is equivocal, and controversy persists about whether NAC affects creatinine level independently of actual kidney function. Study objectives are to investigate whether NAC affects serum creatinine level independently of alterations in other measures of kidney function.

STUDY DESIGN

Double-blind randomized controlled trial.

SETTING & PARTICIPANTS

Patients with stage 3 chronic kidney disease (n = 60), Canada, 2007-2008.

INTERVENTION

Participants were randomly allocated to receive 4 doses of oral NAC (each 1,200 mg) or placebo, administered at 12-hour intervals.

OUTCOME

The primary outcome was change in serum creatinine level between baseline and 4 hours after the last treatment dose. In addition, changes in other parameters of kidney function were measured between baseline and 4, 24, or 48 hours after the last treatment dose.

MEASUREMENTS

Serum creatinine, cystatin C, 24-hour urine protein and creatinine excretion, and creatinine clearance.

RESULTS

60 patients, mean age of 70 years, 75% men, 50% had diabetes, with mean creatinine clearance of 43.7 ± 18.8 (SD) mL/min were enrolled. Between baseline and 4 hours posttreatment, serum creatinine level decreased by 0.044 ± 0.15 mg/dL in the NAC group and 0.040 ± 0.18 mg/dL in the placebo group (95% CI for difference, -0.09 to 0.08; P = 0.9). No significant differences between groups were observed for change in serum creatinine, cystatin C, urine protein, urine creatinine, or creatinine clearance values at any time.

LIMITATIONS

Blinding patients to orally administered liquid NAC is difficult and it is possible that patients receiving NAC were not sufficiently blinded. Effects of NAC beyond 48 hours of treatment were not evaluated.

CONCLUSIONS

In this randomized controlled trial, NAC had no short-term effect on creatinine level and did not decrease urine protein excretion within 48 hours of treatment.

Measuring vs estimating glomerular filtration rate in kidney transplantation

Evaluation of kidney function is crucial in the care of kidney transplant recipients and in the design and interpretation of clinical trials in transplantation. Kidney function is most commonly assessed in both instances using serum creatinine concentration or an estimate of glomerular filtration rate (GFR) based on serum creatinine. These are inexpensive, widely available, and easily administered. Both have significant drawbacks, notably with respect to their inability to accurately identify changes in GFR. Novel markers of GFR such as cystatin C and beta-trace protein show promise as accurate and sensitive markers of GFR but have not yet been adequately evaluated in kidney transplantation. In addition, they are relatively expensive compared to creatinine and their assays are not available in most clinical laboratories. Glomerular filtration rate measurement using a variety of different available tracers and techniques is infrequently used in either clinical care or research protocols because of its cost and cumbersomeness. This review will discuss the merits and pitfalls of the various tools available to evaluate GFR in kidney transplantation.

Exogenous interferences with Jaffe creatinine assays: addition of sodium dodecyl sulfate to reagent eliminates bilirubin and total protein interference with Jaffe methods

BACKGROUND

The study evaluated the impact of interferences on the analytical specificity of three commercial and commonly used creatinine methods (two Jaffe and one enzymatic).

METHODS

Manufacturer creatinine methods plus modified methods were tested with the following interferences: spiking serum with bilirubin, albumin, glucose, hemoglobin and lipid, and patient sera with maximum concentrations of bilirubin, 1,090 micromol/l and protein, 117.8 g/l.

RESULTS

Hemoglobin, 7.5 g/l and lipaemic with triglyceride concentration of 6.27 mmol/l, did not interfere with all assays. Glucose >33.3 mmol/l increased creatinine recovery for Dimension method. Samples spiked with bilirubin imparted a negative bias for Dimension and Architect methods but imparted a positive bias for Vitros assay. However, using patient sera, negative bias with bilirubin was found for all methods, from which Architect method gave the highest effect (R(2)=0.861), followed by Vitros (R(2)=0.239) and Dimension (R(2)=0.163). Protein provided the positive bias for all creatinine measurements that increased with increasing concentration (R(2) ranging from 0.104 to 0.182, P<0.0001). Addition of sodium dodecyl sulfate (SDS) in alkaline-picrate reagent reduced the effect of bilirubin and protein for kinetic Jaffe method. Although adding potassium ferricyanide was well effective for eliminating negative interference of bilirubin, it was prone to interference from protein.

CONCLUSIONS

Endogenous interferences continue to plague creatinine accuracy measurement in both Jaffe and enzymatic methods, and consequentially the estimated glomerular filtration rate. The addition of SDS to the alkaline-pirate reagent was shown to be effective in reducing bilirubin and protein interferences.

Comparison of the predictive performance of eGFR formulae for mortality and graft failure in renal transplant recipients

BACKGROUND

To date, efforts have focused on assessing estimated glomerular filtration rate (eGFR) formulae against measured GFR. However, a more appropriate clinical gold standard is one conveying a defined clinical disadvantage. In renal transplantation, these measures are mortality and graft failure.

METHODS

The Long Term Efficacy and Safety Surveillance database was used to analyze 1344 renal transplant recipients. eGFR was assessed 6 months posttransplantation with the following formulae: Cockcroft-Gault; Walser; Nankivell; abbreviated modification of diet in renal disease (aMDRD); MDRD7; Rule's refitted MDRD; and Mayo Clinic. The outcome measures were mortality and graft failure.

RESULTS

Although eGFR was statistically associated with subsequent mortality and graft failure in the Cox model (irrespective of which eGFR formula was used), the clinical utility of eGFR was moderate at best in predicting subsequent mortality and graft failure. No clinically relevant or statistically significant difference was discernable between formulae, with a maximum area under the receiver operating characteristic curve of 0.63 and 0.61 for 3- and 5-year mortality, respectively, and 0.66 and 0.60 for 3- and 5-year graft failure, respectively. Serum creatinine used in isolation displayed similar predictive utility, and no improvement was seen by investigating the change in creatinine or eGFR between 6 and 12 months.

CONCLUSIONS

In summary, seven eGFR equations showed similar and limited utility in predicting mortality and graft failure after renal transplantation. This has important implications for the management of renal transplant recipients and the use of an eGFR as a surrogate endpoint in clinical trials.

Determination and modelling of clinical laboratory data of healthy individuals and patients with end-stage renal failure

The analyses of 18 biochemical parameters (alanine aminotransferase, albumin, aspartate aminotransferase, calcium, cholesterol, chloride, creatinine, iron, glucose, γ- glutamyl transferase, alkaline phosphatase, phosphorus, potassium, sodium, total protein, triglycerides, uric acid, and urea nitrogen) were performed for 166 healthy individuals and 108 patients with end-stage renal failure (ESRF). The application of cluster analysis proved that there were points of similarity among all 18 biochemical parameters that formed major groups; these groups corresponded to the authors’ assumption of the existence of several overall patterns of biochemical parameters that may be termed “enzyme-specific”; “general health indicator”; “major component excretion”; “blood-specific indicator”; and “protein-specific”. These patterns also appear in the subsets of males and females that were obtained by separation of the general dataset. In addition, the performance of factor analysis similarly proved the validity of this assumption. This projection and modelling method indicated the existence of seven latent factors, which explained 70.05% of the total variance in the system for healthy individuals and more than 72% of the total variance in the system for patients with ESRF. All these results support the probability that a general health indicator could be constructed by taking into account the existing classification groups in the list of biochemical parameters.

[Methods of assessment of the renal function in kidney transplant patients]

Glomerular filtration rate (GFR), which evaluates the evolution of the renal function, can be directly assessed by the measure of urinary or plasmatic clearance of a specific marker that ideally should be freely filtrated, without haemodynamic or toxic effects and easily dosed. Unfortunately, such a sensible marker of renal function variations does not yet exist. Particularly for GFRs in the range of 60ml/min estimation formulas generally over or under-estimate the true GFR, especially the Cockcroft formula that estimates creatinine clearance. Therefore, it is recommended to use validated markers for the measurement of the true GFR (inulin, iohexol, Cr EDTA...), in particular for the follow-up of cohorts and for studies using GFR as an outcome measure. For daily clinical practice, it is possible to use estimation formulas, preferably the 4-variables MDRD equation. However, to optimize the accuracy of GFR measures estimated from these formulas, it is first necessary to control the homogenous calibration of creatinine measurement devices.

Monitoring renal function and limitations of renal function tests

Chronic kidney disease (CKD) is a world-wide public health problem, with adverse outcomes of kidney failure, cardiovascular disease, and premature death. The National Kidney Foundation, through its Kidney Disease Quality Outcome Initiative (K/DOQI) and other National institutions, recommend glomerular filtration rate (GFR) estimates for the definition, classification, screening, and monitoring of CKD. Prediction equations based on serum creatinine values were chosen both for adults (Cockcroft-Gault [C-G] and Modification of Diet in Renal Disease [MDRD] study equations) and for children (Schwartz and Counahan-Barratt equations). This review aims to evaluate from recent literature the clinical efficiency and relevance of these equations in terms of bias, precision, and reproducibility in different specific indications (eg, screening CKD, assessment of disease progression, or therapy efficacy) in different populations. Because these prediction equations based on serum creatinine have limitations, especially in the normal or near-normal GFR range, kidney transplant recipients, and pediatric populations, other prediction equations based on serum cystatin C value were also considered as possibly more sensitive GFR surrogate markers. Recent guidelines state that the cystatin C-based prediction equation cannot be recommended for use in clinical practice. With prediction equations based on serum creatinine, the National Kidney Disease Education Program (NKDEP) recommendations are to report a numerical estimate in round numbers only for GFR values <60 mL/min per 1.73 m(2). The MDRD equation generally outperforms the C-G equation but may still have a high level of bias, depending on creatinine assay calibration, and low precision with, at best, approximately 80% of estimated GFR in the "accuracy range" of 70-130% of the measured GFR value, even in patients with known CKD. According to Kidney Disease Improving Global Outcomes (KDIGO) recommendations, many indications remain for GFR measurements using a clearance method. In that context, it should be recalled that radiolabeled-tracer plasma or urinary clearance methods, are safe, simple, accurate and reproducible.

Accuracy to Estimate Rates of Decline in Glomerular Filtration Rate in Renal Transplant Patients

BACKGROUND

We examined the use of the Cockroft Gault (C-G) test, Modified Diet in Renal Disease 2 (MDRD2) test, and inverse serum creatinine (Delta1/Scr) to estimate rates of decline in renal transplant function using isotope glomerular filtration rate (GFR) as a reference test.

METHODS

Percent changes in estimated GFR (DeltaeGFR) were compared to simultaneous changes in isotope GFR (DeltaiGFR) in 72 patients.

RESULTS

The number of iGFR was 508 with a mean of 7.15+/-3.15 scans per patient. There was a decline in iGFR of 16.14+/-21.37 ml/min over the study duration of 88.9+/-57.6 months. DeltaeGFR and Delta1/Scr correlated significantly with DeltaiGFR. Accuracy to predict DeltaiGFR from the eGFRs was limited to <65% concordance within 30% range from changes in iGFR. Slope analyses showed a significantly lower percent annual loss in mean iGFR of 6.03% than that of the C-G of 8.62% and MDRD2 of 8.96% (P<0.001). The within patient variability measured from the standard deviation (ml/min) of root mean square of 4.69 for iGFR was significantly higher than that for C-G and MDRD2 of 2.46 and 2.94, respectively. iGFR and eGFR at first observation correlated significantly (P<0.001) with last observation.

CONCLUSIONS

iGFR is significantly more variable within patient than the other predictors, and the two estimators predict the iGFR with a high sensitivity but low specificity. This is a clinically reasonable combination. Predicted percent of annual loss in iGFR appears to be smaller than that using the two estimators.

[Creatinine clearance estimation in the extremely elderly subjects]

BACKGROUND

It has been reported that elderly outpatients take at least 6 different kinds of medication.

PURPOSE

To know which formula will best predict creatinine clearance, because 24-hour urine collection is difficult for elderly outpatients.

PATIENTS AND METHODS

We compared four types of formulae (Cockcroft and Gault, Yasuda, Orita, Walser) to estimate creatinine clearance using serum creatinine of 143 elderly inpatients (73 men, 70 women, mean age 82.9 +/- 8.6 years old) including 67 extremely elderly people with various underlying diseases.

RESULT

The formula of Cockcroft and Gault showed the best correlation with creatinine clearance in the extremely elderly subjects (r = 0.74) as well as in people under 85 years (r = 0.76). However, the estimated values of the extremely elderly women were lower than actual creatinine clearance.

CONCLUSION

The formula of Cockcroft and Gault is the best predictive equation of creatinine clearance, except in the extremely elderly women.

A new equation for estimating renal function using age, body weight and serum creatinine

BACKGROUND

Many formulas have been developed to estimate glomerular filtration rate (GFR). The aim of our study was to propose a new, more reliable equation.

METHODS

The study considered 530 subjects (training sample) with M/F 280/250, age 57.1 +/- 17.4, creatinine clearance (CrCl) 55.2 +/- 38.2 (range 2.1-144.0) for the development the new equation. A linear model was used to describe Cr production using serum Cr (sCr), age, and body weight (BW) as variables: (CrCl + b(4)) . sCr = b(1) - (b(2) . age) + (b(3) . BW) subsequently estimating parameter values by linear least squares, with CrCl as the dependent variable, and 1/sCr, age/sCr, BW/sCr as independent variables. CrCl = {[69.4 - (0.59 . age) + (0.79 . BW)]/sCr} - 3.0 (males) and {[57.3 - (0.37 . age) + (0.51 . BW)]/sCr} - 2.9 (females). A 229-patient renal failure validation sample with M/F 166/63, age 53.0 +/- 14.8, GFR 32.0 +/- 14.3 (range 4.3-69.8), assessed using iohexol Cl, was considered to compare the Cockcroft-Gault (C-G) and MDRD formulas with the new equation for estimating GFR.

RESULTS

The mean % error in GFR estimated by the new equation (+2.3 +/- 28.3%) was better than with the C-G and MDRD formulas (+5.2 +/- 30.1% and -11.4 +/- 25.9%, respectively, p < 0.0005 and p < 0.0001), and so was the mean absolute % error, bordering on statistical significance (19.8 +/- 20.3 vs. 21.1 +/- 22.0 and 22.4 +/- 17.3, p = 0.08 and p < 0.005). The precision was also better (RMSE = 7.89 vs. 8.02 and 9.13). The Bland-Altman test showed no GFR over or underestimation trend (measured +/- predicted GFR/2 vs. % error, R2 = 0.001).

CONCLUSIONS

The new equation appears to be at least as accurate as the C-G and MDRD formulas for estimating GFR.

Predicting glomerular filtration rate in kidney transplantation: are the K/DOQI guidelines applicable?

The kidney disease outcomes quality initiative (K/DOQI) guidelines introduced a classification of chronic kidney disease (CKD) based on the level of kidney function. In order to predict the glomerular filtration rate (GFR), they specifically recommended the use of the modification of diet in renal disease (MDRD) study and Cockcroft-Gault (C-G) equations. Since the performance of these estimates has been questioned, we sought to determine whether these recommendations might be applicable in renal transplantation. Following the K/DOQI methodology, we compared the GFR estimated by the MDRD and C-G equations with 476 inulin clearances performed in 284 renal transplant recipients. Even though the MDRD equations provided a better prediction than C-G formula, none of them reached the level of accuracy required by the K/DOQI standards. At least, 25% of the calculated GFR gave a prediction beyond 30% of the corresponding inulin clearance value. In addition, when classified according to their predicted GFR, less than two-thirds of the transplant patients turned out to be assigned to the correct stage of CKD. We conclude that, in renal transplantation, the predictive performance of both C-G and MDRD study equations appears to be particularly impaired and may potentially compromise the validity of the K/DOQI guidelines if implemented in their current form.

Estimating glomerular filtration rate in kidney transplantation: a comparison between serum creatinine and cystatin C-based methods

Accurate measurement of GFR is critical for the evaluation of new therapies and the care of renal transplant recipients. Although not accurate in renal transplantation, GFR is often estimated using creatinine-based equations. Cystatin C is a marker of GFR that seems to be more accurate than creatinine. Equations to predict GFR based on the serum cystatin C concentration have been developed, but their accuracy in transplantation is unknown. GFR was estimated using four equations (Filler, Le Bricon, Larsson, and Hoek) that are based on serum cystatin C and seven equations that are based on serum creatinine in 117 adult renal transplant recipients. GFR was measured using radiolabeled diethylenetriaminepentaacetic acid (99mTc-DTPA), and the bias, precision, and accuracy of each equation were determined. The mean (99m)Tc-DTPA GFR was 58 +/- 23 ml/min per 1.73 m(2). The cystatin C-based equations of Filler and Le Bricon had the lowest bias (-1.7 and -3.8 ml/min per 1.73 m2), greatest precision (11.4 and 11.8 ml/min per 1.73 m2), and highest accuracy (87 and 89% within 30% of measured GFR, respectively). The cystatin C equations remained accurate even when the measured GFR was >60 ml/min per 1.73 m2. The creatinine-based equations were not as accurate, with only 53 to 80% of estimates within 30% of measured GFR. Cystatin C-based equations are more accurate at predicting GFR in renal transplant recipients than traditional creatinine-based equations. Further prospective studies with repetitive measurement of cystatin C are needed to determine whether cystatin C-based estimates of GFR will be sufficiently accurate to monitor long-term allograft function.

Integrating regression formulas and kernel functions into locally adaptive knowledge-based neural networks: a case study on renal function evaluation

OBJECTIVE

In many medical areas, there exist different regression formulas to predict/evaluate a medical outcome on the same problem, each of them being efficient only in a particular sub-space of the problem space. The paper aims at the development of a generic, incremental learning model that includes all available regression formulas for a particular prediction problem to define local areas of the problem space with their best performing formula along with useful explanation rules. Another objective of the paper is to develop a specific model for renal function evaluation using nine existing formulas.

METHODS AND MATERIALS

We have used a connectionist neuro-fuzzy approach and have developed a knowledge-based neural network model (KBNN) which incorporates and adapts incrementally several existing regression formulas and kernel functions. The model incorporates different non-linear regression functions as neurons in its hidden layer and adapts these functions through incremental learning from data in particular local areas of the space. More specifically, each hidden neural node has a pair of functions associated with it--one regression formula, that represents existing knowledge and one Gaussian kernel function, that defines the sub-space of the whole problem space, in which the formula is locally adapted to new data. All these functions are aggregated and changed through incremental learning. The proposed KBNN model is illustrated using a medical dataset of observed patient glomerular filtration rate (GFR) measurements for renal function evaluation. In this case study, the regression function for each cluster is selected by the model from nine formulas commonly used by medical practitioners to predict GFR. 441 GFR data vectors from 141 patients taken from 12 sites in Australia and New Zealand have been used as a case study experimental data set.

RESULTS

The proposed GFR prediction model, based on the proposed generic KBNN model, outperforms at least by 10% accuracy any of the individual regression formulas or a standard neural network model. Furthermore, we have derived locally adapted regression formulas to perform best on local clusters of data along with useful explanatory rules.

CONCLUSION

The proposed KBNN model manifests better accuracy then existing regression formulas or neural network models for renal function evaluation and extracts modified formulas that perform well in local areas of the problem space.

Predictive performance of renal function equations in renal transplant recipients: an analysis of patient factors in bias

Creatinine-based equations are available to estimate GFR. After renal transplantation body composition usually changes, thus specific validation is required for transplant recipients. Nine equations were compared with iothalamate glomerular filtration rate (GFR) at 1 year after transplantation in 798 recipients. Equations were analyzed for precision, bias and accuracy. Sources of bias were analyzed by univariate and multivariate analysis, with body mass index (BMI), age and sex as independent variables and bias as dependent variable. Four hundred and seventy-eight patients were studied to assess whether the equations can be used to monitor renal function over time. Predictive performance was modest for all equations. MDRD and Jelliffe 2 were the best predictors of GFR. Bias was significantly related to BMI, age and gender in most equations. Multivariate analysis confirmed their independent contribution to the bias of MDRD, Jelliffe 2 and most other equations. Over time, bias was relatively stable at group level, but predictive performance in individuals was modest. The predictive performance of renal function equations is modest in renal transplants, which hampers their use for accurate assessment of renal function in the individual. The role of patient factors in the systematic error suggests that development of better equations should be feasible by better incorporation of these factors.

Chronic renal allograft dysfunction

The major causes of renal transplant loss are death from vascular, malignant or infectious disease, and loss of the allograft from chronic renal dysfunction associated with the development of graft fibrosis and glomerulosclerosis. Chronic allograft nephropathy (CAN) is the histologic description of the fibrosis, vascular and glomerular damage occurring in renal allografts. Clinical programs rely on monitoring change in serum creatinine for identification of patients at risk of CAN, but this change occurs late in the course of the disease, and underestimates the severity of pathologic change. CAN has several causes: ischemia-reperfusion injury, ineffectively or untreated clinical and subclinical rejection, and superimposed calcineurin inhibitor nephrotoxicity, exacerbating pre-existing donor disease. Once established, interstitial fibrosis and arteriolar hyalinosis lead to progressive glomerulosclerosis over the subsequent years. There have been a number of approaches to treatment aimed at reducing the impact of CAN, mostly centered around avoidance of calcineurin inhibitors through their elimination in all, or just selected, patients. These immunosuppression strategies combine corticosteroids with azathioprine or mycophenolate mofetil, and/or sirolimus and everolimus. Late identification of CAN in individual patients has meant that strategies for intervening to prevent chronic renal allograft dysfunction and subsequent graft loss tend to be "too little and far too late."

Evolving connectionist system versus algebraic formulas for prediction of renal function from serum creatinine

BACKGROUND

In clinical trials, equation 7 from the Modification of Diet in Renal Disease (MDRD) Study is the most accurate formula for the prediction of glomerular filtration rate (GFR) from serum creatinine. An alternative approach has been developed using evolving connectionist systems (ECOS), which are novel computing structures that can be trained to generate accurate output from a given set of input variables. This study aims to compare the prediction errors associated with each method, using data that reproduce routine clinical practice as opposed to the artificial setting of clinical trials.

METHODS

The methods were compared using 441 radioisotope measurements of GFR in 178 chronic kidney disease patients from 12 centers in Australia and New Zealand. All clinical and laboratory measurements were obtained from the patients' center rather than central laboratories, as would be the case in routine clinical practice. Both the MDRD formula and ECOS used the same predictive variables, and both were optimized to the study cohort by stepwise regression and training, respectively.

RESULTS

Mean measured GFR in the cohort was 22.6 mL/min/1.73 m(2). The bias and precision of the MDRD formula were -3.5 mL/min/1.73 m(2) and 34.5%, respectively, improving to -1.2 mL/min/1.73 m(2) and 31.1% after maximal optimization of the formula to study data. The bias and precision of the ECOS were 0.7 mL/min/1.73 m(2) and 32.6%, respectively, improving to -0.1 mL/min/1.73 m(2) and 16.6% after maximal optimization of the system to study data. The prediction of GFR using ECOS was improved by accounting for the center from where clinical and laboratory measurements originated within the connectionist model.

CONCLUSION

Algebraic formulas will be associated with greater prediction error in routine clinical practice than in the original trials, and machine intelligence is more likely to predict GFR accurately in this setting.

Limitations of glomerular filtration rate equations in the renal transplant patient

This study aims to compare the performance of endogenous creatinine clearance (CL(cr)) and a number of published mathematical equations to calculate glomerular filtration rate (GFR) in renal transplant patients considering (99m)Tc DTPA isotope scan as the reference method. A total of 152 GFR were performed on 81 renal transplant patients. Accuracy of each method was measured at different percentiles. The bias and precision of all the methods were then compared. A paired t-test was used to compare the performance of each calculation to the respective GFR measured by isotope study performed on the same day. In the total population, all calculated methods correlated significantly with the isotope results. Accuracies within specific ranges of the isotope GFR were limited in all equations (agreement with isotope result </=72% at 30% accuracy range in the total group). Within the limited accuracy, Edwards' equation (K.D. Edwards and H.M. Whyte, Australas Ann Med 1959; vol. 8: p. 218) had the least bias in the total population. Bjornsson (T.D. Bjornsson, Clin Pharmacokinet 1979; vol. 4: p. 200) had the least bias in patients with GFR >/= 50 mL/min and Gates in patients with GFR < 50 mL/min. Salazar (D.E. Salazar and G.B. Corcoran, Am J Med 1988; vol. 84: p. 1053) had the least bias in patients with BMI above 30 kg/m(2) and the Davis equation (G.A. Davis and M.H. Chandler, Am J Health Syst Pharm 1996; vol. 53: p. 1028) in patients with BMI <25 kg/m(2). In all analyses, Nankivell (B.J. Nankivell, S.M. Gruenwald, R.D.M. Allen and J.R. Chapman, Transplantation 1995; vol. 59: p. 1683) overestimated GFR by more than 80% and MDRD 1 and 2 in <10% of the time. The results demonstrate the inherited limitation in the currently available equations to calculate GFR in renal transplant patients.

Transrenal fixation of aortic stent-grafts: current status and future directions

Aortic stent-graft repair has been widely used in clinical practice for more than a decade, achieving satisfactory results compared to open surgical techniques. Transrenal fixation of stent-grafts is designed to obtain secure fixation of the proximal end of the stent-graft to avoid graft migration and to prevent type I endoleak. Unlike infrarenal deployment of stent-grafts, transrenal fixation takes advantage of the relative stability of the suprarenal aorta as a landing zone for the uncovered struts of the proximal stent. These transostial wires have sparked concern about the patency of the renal arteries, interference with renal blood flow, and effects on renal function. Although short to midterm results with suprarenal stent-grafts have not shown significant changes in renal function, long-term effects of this technique are still not fully understood. This review will explore the current status of transrenal fixation of aortic stent-grafts, potential risks of stent struts relative to the renal ostium, alternative methods to preserve blood flow to the renal arteries, and future directions or developments in stent-graft design to prevent myointimal proliferation around the stent struts.

Performance of different prediction equations for estimating renal function in kidney transplantation

Numerous formulas have been developed to estimate renal function from biochemical, demographic and anthropometric data. Here we compared renal function derived from 12 published prediction equations with glomerular filtration rate (GFR) measurement by plasma iohexol clearance as reference method in a group of 81 renal transplant recipients enrolled in the Mycophenolate Mofetil Steroid Sparing (MY.S.S.) trial. Iohexol clearances and prediction equations were carried out in all patients at months 6, 9 and 21 after surgery. All equations showed a tendency toward GFR over-estimation: Walser and MDRD equations gave the best performance, however not more than 45% of estimated values were within +/-10% error. These formulas showed also the lowest bias and the highest precision: 0.5 and 9.2 mL/min/1.73 m2 (Walser), 2.7 and 10.4 mL/min/1.73 m2 (MDRD) in predicting GFR. A significantly higher rate of GFR decline ranging from -5.0 mL/min/1.73 m2/year (Walser) to -7.4 mL/min/1.73 m2/year (Davis-Chandler) was estimated by all the equations as compared with iohexol clearance (-3.0 mL/min/1.73 m2/year). The 12 prediction equations do not allow a rigorous assessment of renal function in kidney transplant recipients. In clinical trials of kidney transplantation, graft function should be preferably monitored using a reference method of GFR measurement, such as iohexol plasma clearance.

Assessing renal graft function in clinical trials: Can tests predicting glomerular filtration rate substitute for a reference method?

BACKGROUND

In clinical trials, comparison of renal graft function needs a rigorous determination of glomerular filtration rate (GFR). Since reference methods to measure GFR cannot be easily implemented, a number of tests predicting GFR are usually used. However, little is known about their validity in renal transplant patients. We aimed to compare the performances of six GFR tests with inulin clearance in this population.

METHODS

Five hundred consecutive inulin clearances performed in 294 renal transplant recipients with stable renal function were retrospectively selected. For each of them, we computed six estimates: the 24-hour creatinine clearance, the Cockcroft-Gault, Walser, Jelliffe, Nankivell, and Levey formulas. Their respective performance was assessed by correlation (simple linear regression), accuracy (dispersion of true error), and agreement (Bland and Altman method).

RESULTS

Each GFR test closely correlated with inulin clearance (P < 0.0001). Comparisons between pairs of GFR tests did not show any significant difference in accuracy between the Levey, Jelliffe, and Walser formulas. Conversely, each of these formulas demonstrated a significant lower dispersion (P < 0.005) than the others. Nevertheless, all GFR tests displayed considerable lack of agreement with limits of agreement over 40 mL/min/1.73 m2 apart. The proportion of predicted GFR differing from inulin clearance by +/- 10 mL/min/1.73 m2, ranged from 34% for the Jelliffe formula to 53% for the Nankivell's one.

CONCLUSION

None of these formulas seems to be able to safely substitute for inulin clearance. In clinical trials, renal graft function should be preferably assessed using a reference method of GFR measurement.

Predicted creatinine clearance to evaluate glomerular filtration rate in black Caribbean subjects

BACKGROUND AND METHODS

Although Caribbean people have been a lesser-studied ethnic group than other populations, they have a high burden of hypertension and renal disease. Because Caribbean people have a greater muscle mass than Caucasians, this study examined the accuracy of creatinine-based estimates (creatinine clearance; C(cr) and Cockcroft-Gault formula; C-G Cl) of glomerular filtration rate (GFR) in 38 Caribbeans who were matched for age, gender, and GFR, with 38 Caucasian subjects. Patients were considered black Caribbean if at least one of two parents was of black Caribbean origin. GFR values ranging from 5 to 140 ml/min/1.73 m(2) were measured by inulin clearance. Results were compared using linear correlations and the Bland and Altman methodology to provide better estimates of value dispersion.

RESULTS

Correlation coefficients between C-G Cl and GFR were highly significant in both black Caribbean subjects (r=0.83, P<0.001) and Caucasians (r=0.84, P<0.001). Similar coefficients were obtained between C(cr) and GFR (r=0.89, P<0.001 and r=0.90, P<0.001, respectively). In spite of these strong correlations, the Bland and Altman representation highlighted huge intra-individual variations in GFR estimation by C-G Cl and by C(cr) in both ethnic groups. The underestimation of GFR by C-G Cl was significant in black Caribbeans (-8.6+/-20 ml/min/1.73 m(2), P<0.001) but not in Caucasians (-5.6+/-20.7 ml/min/1.73 m(2)). C(cr) overestimation of GFR was significant both in Caribbeans (8.7+/-16.8 ml/min/1.73 m(2), P<0.001) and in Caucasians (7.2+/-15.7 ml/min/1.73 m(2), P<0.01).

CONCLUSIONS

The C-G formula for estimating GFR yields similar clinical values in black Caribbeans and in Caucasians, but the same limitations were observed in both ethnic groups.

The reliability of different formulae to predict creatinine clearance

OBJECTIVES

Creatinine clearance (CCR) is a commonly used tool to measure glomerular filtration rate (GFR) in clinical practice. This tool requires collection of 24-h urine, which is quite bothersome. Several different formulae have been used to estimate GFR using plasma creatinine and other easy formulae to obtain biometrical data. We examined 10 formulae and compared them with actually measured CCR in a large sample of the general population.

DESIGN

Cross-sectional cohort study.

SETTING

University hospital outpatient clinic, a population based study.

SUBJECTS

A total of 8592 inhabitants of the city of Groningen, 28-75 years of age. The cohort is enriched for microalbuminuria.

RESULTS

In general, the formulae did not give an accurate estimation of CCR, particularly not in male and in obese subjects. Six formulae, including the Cockcroft-Gault gave a fairly good estimation of CCR in the overall population and in subgroups of specific gender, body mass index and age. All formulae however, gave an underestimation of the measured CCR in higher ranges of CCR and an overestimation in the lower ranges. Moreover, the age-related decline of CCR is hard to approximate with a formula.

CONCLUSIONS

We conclude that formulae to estimate CCR in the general population, although giving a fairly good estimate of mean CCR, do not offer reliable data on CCR in the upper and lower ranges and do not adequately estimate the age-related decline in CCR.

Measurement of renal function in pre-ESRD patients

The measurement of renal function in pre-dialysis patients is important in order to determine the appropriate time to begin renal replacement therapy, to forecast the start, and to compare, in groups of patients, the efficiency of different treatments that limit renal disease progression. The most reliable methods, such as inulin clearance or measurement by radioisotopes, are too awkward for the usual clinical follow-up of patients. Although much simpler and almost as reliable, the use of iohexol radiologic contrast does not allow the frequent monitoring of the patient either. The determinations of the plasmatic creatinine and its clearance or the estimate of the glomerular filtration rate by means of equations derived from the creatinine are the methods most often used in order to measure renal function, although not without problems in pre-dialysis. In order to try to overcome such problems, more precise equations and procedures, including the measurement of averaged urea-creatinine clearance or creatinine clearance with cimetidine, have been designed that better estimate the glomerular filtration rate. However, none of these methods is totally reliable in pre-dialysis. A new endogen marker, cystatin C, has advantages over creatinine, though more studies are needed in pre-dialysis in order to ascertain its use. The initial proposal of the National Kidney Foundation's Kidney Disease Outcome Quality Initiative (DOQI) guidelines to use weekly Kt/V and nutritional parameters to determine the time for starting renal replacement therapy has widened the prospects of the debate on the measurement of renal function in pre-dialysis, but further work is required to define their role in pre-dialysis patients' follow-up.

Prediction equations to estimate glomerular filtration rate: an update

The level of glomerular filtration rate can be estimated from the serum creatinine concentration and other easily measured patient variables from prediction equations developed using multivariable regression techniques. Recently, a new equation has been developed from the Modification of Diet in Renal Disease study, which is more accurate than other equations and more accurate than measurement of creatinine clearance. The authors recommend using prediction equations in clinical practice to estimate the level of glomerular filtration rate.

Evaluation of renal Kt/V as a marker of renal function in predialysis patients

BACKGROUND

The use of renal Kt/V (r-Kt/V) as an indicator for the need of dialysis initiation has been recommended in the NKF-DOQI guidelines. In analogy to clinical practice in peritoneal dialysis, a fall of r-Kt/V below a threshold of 2.0 per week may indicate inadequate renal toxin elimination. However, there are no studies linking r-Kt/V with other parameters of glomerular filtration rate (GFR) in predialysis patients, and the validity of r-Kt/V as parameter for timing of dialysis initiation is unknown.

METHODS

Renal function was assessed repeatedly in 125 patients (N = 465 measurements). In predialysis patients (r-Kt/V <2.5 per week) r-Kt/V was compared with creatinine [CCr], urea [CUr], averaged creatinine/urea clearance [CCr/Ur], Cockcroft-Gault formula [CCG], and MDRD prediction equation 6 (MDRD6-GFR). The diagnostic performance of r-Kt/V as a parameter for timing the initiation of dialysis was evaluated.

RESULTS

Renal Kt/V <2.5 was prevalent in 24.9% of cases (N = 116, mean 1.92 +/- 0.34). In this group mean CCr was 13.8 +/- 4.9, mean CUr 6.7 +/- 1.3, and CCr/Ur 10.2 +/- 2.9 mL/min/1.73 m2. There was no correlation of r-Kt/V with serum creatinine and MDRD6-GFR, but a significantly positive correlation with CCr/Ur (r2 = 0.3382, P < 0.001). Sensitivity of r-Kt/V to detect CCr/Ur < 10.5 mL/min/1.73 m2, defined as the threshold for dialysis initiation, was 73.6% with a specificity of 91.9%.

CONCLUSIONS

These results suggest that r-Kt/V is a parameter of acceptable specificity but poor sensitivity for the timing of dialysis initiation. Additional measures of renal function, such as the average of measured creatinine and urea clearance, also should be taken into consideration when deciding on the timing of dialysis initiation prior to the development of clinical signs of uremia and malnutrition.

No evidence of accelerated loss of kidney function in living kidney donors: results from a cross-sectional follow-up

BACKGROUND

There is a lack of kidneys available for kidney transplantation, and living donors are increasingly used. It is important to examine the possible long-term adverse affect on the renal function and blood pressure of the donors.

METHODS

We have made a comprehensive follow-up of all living kidney donors at our center from 1964 to 1995. Of 402 donors still alive, we were able to get information about serum creatinine, urinary proteins, and blood cells in urine using reagent strips, and blood pressure from 87%. The glomerular filtration rate (GFR) was estimated using a formula and was measured with Iohexol clearance in 43 of the donors. Individual data on GFR and the prevalence of hypertension were compared with the age- and gender-expected values.

RESULTS

The mean age of the examined donors was 61 years (SD:13) at follow-up, and the time since donation was 12 years (SD:8). The average estimated GFR was 72% (SD:18) of the age-predicted value. The ratio of the estimated to the predicted GFR showed no correlation to the time since donation, indicating that there is no accelerated loss of renal function after donation. GFR below 30 ml/min was found in five donors. No donor died in uremia or had dialysis treatment before death. However, three donors developed renal disease, and one was in dialysis treatment. In two of these cases, hereditary factors were possibly involved. Hypertension was present in 38% of the donors but the age-adjusted prevalence of hypertension among donors was not higher than in the general population. Significant proteinuria (> or =1.0 g/L) was found in 3% and slight proteinuria (<1.0 g/L) in 9% of the donors. Proteinuria was associated with hypertension and a lower GFR.

CONCLUSIONS

On average, the remaining renal function of kidney donors did not deteriorate more rapidly than what may be expected from ageing. However one-third of the female and half of the male donors developed hypertension and, approximately, 10% displayed proteinuria. Nevertheless, our study supports the continued use of living kidney donors if strict criteria are used for acceptance.

Chromium-51 ethylenediamine tetraacetic acid glomerular filtration rate: a better predictor than glomerular filtration rate calculated by the Cockcroft-Gault formula for renal involvement in systemic lupus erythematosus patients

OBJECTIVE

To investigate whether the ethylenediamine tetraacetic acid (EDTA) glomerular filtration rate (GFR) is a better indicator of the degree of renal involvement than serum creatinine concentration or creatinine clearance calculated by the Cockroft-Gault formula.

METHODS

We studied prospectively all systemic lupus erythematosus (SLE) patients with normal or borderline serum creatinine concentration (<110 micromol/l) and urinary sediment abnormalities and/or proteinuria in the last 2 yr. EDTA-GFR, serum creatinine concentration, calculated creatinine clearance (Cockroft-Gault formula) and 24-h urine protein were determined at the same time. Renal biopsies were performed in patients with low values of EDTA-GFR or significant proteinuria.

RESULTS

Twenty-three patients were identified, of whom 22 were females. The average age of the patients was 31.6+/-8.2 yr. Biopsies were assigned to WHO classes as follows: class II, 1 patient; class III, 6 patients; class IV, 10 patients; class V, 6 patients. The average serum creatinine concentration, EDTA-GFR and calculated creatinine clearance were 79.8+/-mol/l, 74.5 ml/min and 97 ml/min respectively. EDTA-GFR showed abnormal values (<80 ml/min) in 15 of the 23 patients (65.2%) while calculated creatinine clearance was abnormal (<80 ml/min) in three of the 23 patients (13%) (P<0.001). Using the Pearson correlation test, we did not find any correlation between EDTA-GFR or creatinine clearance values and the sum of activity and chronicity indices.

CONCLUSION

GFR performed by EDTA-GFR correctly predicted renal involvement in SLE patients, whereas GFR calculated by the Cockcroft-Gault formula may have underestimated renal function. Significant numbers of patients with WHO class III, IV or V lupus nephritis may be missed if biochemical creatinine clearance or serum creatinine concentration alone is used to assess renal disease.

The influence of ketoacids on plasma creatinine assays in diabetic ketoacidosis

OBJECTIVE

Analysis of the interference of ketoacids on various routine plasma creatinine assays during a clinical episode of diabetic ketoacidosis (DKA).

DESIGN

Observational study. Blood samples were drawn before, during and after standard in-hospital treatment. Plasma creatinine was measured with two dissimilar enzymatic assays (creatininase PAP + and creatinine iminohydrolase Serapak), a kinetic alkaline picrate method (Jaffé) and a high-performance liquid chromatography (HPLC) procedure. Acetoacetate and beta-hydroxybutyrate were analysed by enzymatic methods.

SETTING

Department of Medicine, University Hospital.

SUBJECTS

Nine patients who experienced 10 episodes of DKA.

MAIN OUTCOME MEASURES

Agreement of the routine plasma creatinine assays with HPLC and analysis of possible interferents.

RESULTS

At presentation, the Jaffé assay gave falsely high values of plasma creatinine (median 99 micromol L(-1)), in contrast to the PAP+ (median 60.5 micromol L(-1)) and HPLC assays (median 67.5 micromol L(-1)). This positive error decreased during treatment. This was due to a decrease in acetoacetate, as the positive error by the Jaffé method correlated with the acetoacetate concentration (r = 0.79, P < 0.0001). In the multiple regression analysis, beta-hydroxybutyrate caused no additional interference by the Jaffé assay, confirmed by in vitro experiments. Analysis of agreement showed that the difference between PAP+ and HPLC creatinine was -4.6 +/- 3.0 micromol L(-1) (mean +/- SD), and 2.0 +/- 5.3 micromol L(-1) between Serapak and HPLC. This was statistically significant, but clinically negligible.

CONCLUSION

Acetoacetate caused severe interference of the alkaline picrate (Jaffé) assay, which might influence therapeutic decisions at the start of diabetic ketoacidosis. Enzymatic assays lack this interference.

Changes in conjugated linoleic acid and its metabolites in patients with chronic renal failure

BACKGROUND

Conjugated linoleic acid (CLA) is a mixture of isomers of linoleic acid with conjugated double bonds that constitutes the most abundant fatty acid with conjugated dienes (CDs) in humans. CLA, erroneously considered in the past as a product of lipoperoxidation, has a dietary origin and has shown to possess anticarcinogenic and anti-atherogenic activity, mainly in animal studies. CLA can be metabolized to conjugated linolenic acid (CD18:3) and to conjugated eicosatrienoic acid (CD20:3) and these metabolites may be implicated in CLA activity. Because of the presence of dyslipidemia and the high incidence of cardiovascular and neoplastic diseases in uremic patients, we evaluated CLA and its metabolites in these patients in order to evaluate their metabolism and site distribution.

METHODS

We measured CLA, CD18:3, CD20:3, CD fatty acid hydroperoxides (lipoperoxidation products), and linoleic acid in the plasma, adipose tissue, and red blood cell (RBC) membranes by using high-pressure liquid chromatography in the following groups: (1) 23 chronic renal failure (CRF) patients with creatine clearance (CCr)> 10 mL/min (26.2 +/- 16.7); (2) 21 end-stage CRF patients in conservative treatment with CCr <10 mL/min (6.8 +/- 1.8); (3) 30 hemodialysis (HD) patients; and (4) 30 healthy controls.

RESULTS

The incorporation of CLA, CD18:3, and CD20:3 in RBC membranes was significantly reduced in group 1 and was even more reduced in groups 2 and 3. CLA significantly increased both in the plasma and adipose tissue of end-stage CRF patients only. CD18:3 and CD20:3 did not change in the plasma and adipose tissue of any group. No significant changes in linoleic acid and CD fatty acid hydroperoxides were found.

CONCLUSIONS

The alterations of CD in CRF patients are not due to lipoperoxidation. The increased levels of CLA in plasma and adipose tissue of end-stage CRF patients may be due either to a reduced metabolization of CLA to CD18:3 and CD20:3, or to an altered site distribution with reduced incorporation in cellular membranes and accumulation in the plasma and adipose tissue. The clinical significance of these changes remains to be investigated.

Survival advantage in Asian American end-stage renal disease patients

Survival advantage in Asian American end-stage renal disease patients.

BACKGROUND

An earlier study documented a lower mortality risk for end-stage renal disease (ESRD) patients in Japan compared with the United States. We compared the mortality of Caucasian (white) and Asian American dialysis patients in the United States to evaluate whether Asian ancestry was associated with lower mortality in the United States.

METHODS

The study sample from the U.S. Renal Data System census of ESRD patients treated in the United States included 84,192 white or Asian patients starting dialysis during May 1995 to April 1997, of whom 18,435 died by April 30, 1997. Patient characteristics were described by race. Relative mortality risks (RRs) for Asian Americans relative to whites were analyzed by Cox proportional hazards regression models adjusting for characteristics and comorbidities. Population death rates were derived from vital statistics for the United States and Japan by age and sex.

RESULTS

Adjusting for demographics, diabetes, comorbidities, and nutritional factors, the RR for Asian Americans was 0.75 (P = 0.0001). Race-specific background population death rates accounted for over half of the race-related mortality difference. For whites, mortality decreased as the body mass index (BMI) increased. For Asians, the relationship between BMI and survival was u-shaped. The ratio of Asian American/white dialysis death rates and the ratio of Asian American/white general population death rates both varied by age in a similar pattern. The population death rates of Asian American and Japanese were also similar.

CONCLUSION

Among dialysis patients, Asian Americans had a markedly lower adjusted RR than whites. The effect of BMI on survival differed by race. Compared with the respective general population, dialysis patients had the same relative increase in death rates for both races. The difference in death rates between the United States and Japan does not appear to be primarily treatment related, but rather is related to background death rates.

How to assess glomerular function and damage in humans

In human subjects, the assessment of renal function and of its changes by interventions is limited to the measurement of glomerular filtration rate (GFR), renal blood flow and the estimation of proteinuria. In humans, GFR can be determined exactly by measuring the clearance of an ideal filtration marker, such as inulin. The classic method of measuring inulin clearance in humans includes constant intravenous infusion of the compound and timed collections of urine. In order to avoid the need for timed urine collections, a number of alternative procedures have been devised. All these methods only use determinations of inulin in plasma or serum. From these, the total body inulin clearance is obtained using pharmacokinetic calculations. In order to measure total body clearance, usually called plasma clearance, inulin is either given as a constant intravenous infusion or as a bolus infusion. Both procedures overestimate GFR because of incomplete distribution of inulin during the study periods. The error may be minimized by using model-independent pharmacokinetic calculations. Unlike inulin, creatinine is not a perfect filtration marker. This is because the substance is not only eliminated by glomerular filtration but also by tubular secretion. The extent of tubular creatinine secretion is not constant in various individuals. Serum creatinine concentration is a commonly used measure of renal function in clinical practice. This parameter is determined both by the renal elimination and by the production of the compound. Differences in creatinine production among subjects and over time in a single individual may occur because of changes in muscle mass. Radioisotopic filtration markers can easily and accurately be measured in plasma and serum. Using this method, the plasma concentration-time curve of these compounds can easily be studied after intravenous bolus injection. From the plasma concentration-time curves obtained, the total body clearance (plasma clearance) of the substances can be calculated using pharmacokinetic models. Most frequently, 125l-iothalamate, 99mTc-diethylenethiaminepenta-acetic acid and 51Cr-ethylenediaminetetra-acetic acid are used for the estimation of GFR in humans. The total body clearance of all these filtration markers overestimates GFR. The error induced by this phenomenon is particularly relevant at low levels of GFR. In recent years, iohexol has been used as a filtration marker. The substance can be measured in plasma, serum and urine using high-performance liquid chromatography. So far, good agreement has been shown for GFR determined by the classic inulin clearance and by the iohexol plasma clearance. Screening for proteinuria is commonly performed using reagent test strips. Quantitative measurements of marker proteins can be used to estimate the extent and the site of damage in the nephron. These measurements may be used to estimate the progression of renal disease and the response to therapeutic interventions. Of particular interest is the degree of albuminuria which indicates nephropathy in diabetic patients and end-organ damage in patients with hypertension.

The effect of angiotensin II receptor antagonists on kidney function in two-kidney, two-clip Goldblatt hypertensive rats

The effect of blockade of the renin-angiotensin system on kidney function using non-peptide angiotensin AT1 receptor antagonists was investigated in renovascular hypertensive rats. An angiotensin converting enzyme inhibitor, captopril and two angiotensin AT1 receptor antagonists, losartan and GR138950 (1-([3-bromo-2[2-[[(trifluoro-methyl)sulphonyl]amino]phenyl]-5 benzofuranyl]methyl)-4-cyclopropyl-2-ethyl-1H-imidazole-5-carboxamide) were administered in Na+-deplete two-kidney, two-clip Goldblatt hypertensive rats over a 3-day period. Captopril, losartan (30 mg/kg body weight) and GR138950 (5 mg/kg body weight) significantly (P < 0.001) lowered the systolic blood pressure in the hypertensive rats from 290 +/- 5, 252 +/- 9 and 238 +/- 13 mmHg to 152 +/- 17, 148 +/- 9 and 123 +/- 6 mmHg, respectively. The magnitude of reduction in blood pressure in these three groups of rats was similar and occurred with comparable marked increases in plasma levels of urea and creatinine indicative of acute renal failure. These findings demonstrate an important role for angiotensin II in the maintenance of renal function during blood pressure reduction in renovascular hypertensive states during restriction of dietary Na+ intake.

Measurement of Gd-DTPA dialysis clearance rates by using a look-locker imaging technique

The exponential clearance rate constant, (kappa), and filtration fraction (FF) have been measured for dialysis of Gadolinium-diethylenetriaminepentaacetic acid (Gd-DTPA) (Magnevist, Berlex, Wayne, NJ) solutions by using a Look-Locker imaging technique under conditions of flow. The measured values of kappa for the Baxter CA-50, CA-110, and CA-210 filters were 0.0037 +/- 0.0003, 0.0057 +/- 0.0017, and 0.0092 +/- 0.0018 min-1, respectively, for dialysis of 4.0 liters of aqueous Gd-DTPA solutions. The measured values of FF for the Baxter CA-110 and CA-210 filters were 0.060 +/- 0.013 and 0.089 +/- 0.015, respectively, for dialysis of aqueous Gd-DTPA at 350 ml/min. The kappa and FF measurements agree with values that use inversion recovery (IR) on static samples obtained by drawing aliquots of solution during the course of dialysis. This in vitro experiment suggests that accurate in vivo measurements of filtration fraction and glomerular filtration rate (GFR) may be possible.

Treatment of nephrotic adults with a supplemented, very low-protein diet

Optimal dietary protein intake for adults with the nephrotic syndrome has not been established; very low-protein diets are believed to be contraindicated. Sixteen patients with the nephrotic syndrome were nevertheless prescribed a very low protein diet (0.3 g/kg) supplemented by 10 to 20 g/d essential amino acids (or, in a few cases, ketoacids) for an average of 10 months (range, 1 to 36 months). In 11 patients with initial glomerular filtration rates (GFRs) < or = 30 mL/min/3 m2 of height (ht)2, significant but modest improvement was seen (on the average) in proteinuria, serum albumin, and serum cholesterol; all 11 eventually went on to dialysis. The other five patients, with initial GFRs of 32 to 69 ml/min/3 m2 of ht2, had either focal segmental glomerulosclerosis, diabetic nephropathy, or, in one patient, both. The nephrotic syndrome associated with these disorders rarely remits spontaneously. However, during the following 3 to 15 months mean proteinuria decreased from 9.3 to 1.9 g/d, mean serum albumin increased from 2.5 g/dL to 3.8 g/dL, and mean serum cholesterol decreased from 415 mg/dL to 255 mg/dL (all P < 0.001). The GFR either remained constant or increased. Four of these five patients have resumed normal or nearly normal diets and remain in remission or near-remission for 6 to 24 months. We conclude that severe protein restriction plus an essential amino acid supplement may induce prolonged remission in adults with the nephrotic syndrome provided that GFR is not severely reduced. The mechanism of this paradoxical response to protein restriction remains to be determined.

Iodinated contrast media-induced nephropathy: pathophysiology, clinical aspects and prevention

Administration of iodinated contrast media (CM) for radiographic purposes is a preoccupying cause of acute renal failure. This review of the literature deals with what is known about physiopathology, clinical course, risk factors and prevention. Factors involved in the pathophysiology of CM-induced acute renal failure are vasoconstriction, direct tubular cell injury and tubular obstruction by casts. In the case of pre-existing renal hypoperfusion, CM may disturb the complex interaction between factors which modulate renal haemodynamics by increasing vasoconstrictor factors, notably endothelin peptides. The renal medulla, a zone characterized by a high metabolic activity and a low oxygen tension, may be a specific target for CM-induced effects. CM-induced nephropathy (CMN) is essentially observed in patients with one or more associated risk factors (chronic renal failure, dehydration, diabetes mellitus with impaired renal function, multiple myeloma, large CM volume, intra-arterial rather than intravenous route, etc). There is much debate as to whether newer low osmolar CM (LOCM) are better tolerated than conventional high osmolar CM (HOCM). Most of the animal studies clearly demonstrate the advantages of LOCM over HOCM. Clinical literature is far more confusing, although some recent studies and one meta-analysis demonstrate that LOCM are better tolerated in patients with impaired renal function. The low number of comparative clinical trials carried out in high risk patients, wide variability in CMN definitions, limited number of patients enrolled and inadequacy of various selected endpoints may explain difficulties experienced in demonstrating this advantage. Furthermore, while hydration is correctly maintained during clinical trials, this is not always true in clinical practice. Such a discrepancy could lead to underestimation of the potential advantage of LOCM over HOCM. Effective prevention should associate the correct hydration of patients, identification and, when possible, optimal correction of risk factors, avoidance of repeated CM injections within a short period of time and temporary disruption of treatment with other nephrotoxic drugs (non steroidal antiinflammatory drugs, aminoglycosides, etc).