Serial assessment of glomerular filtration rate in lupus nephropathy

Measured Glomerular Filtration Rate: The Query for a Workable Golden Standard Technique

Inulin clearance has, for a long time, been considered as the reference method to determine measured glomerular filtration rates (mGFRs). However, given the known limitations of the standard marker, serum creatinine, and of inulin itself, and the frequent need for accurate GFR estimations, several other non-radioactive (iohexol and iothalamate) and radioactive (51Cr-EDTA, 99mTc-DTPA, 125I iothalamate) exogenous mGFR filtration markers are nowadays considered the most accurate options to evaluate GFR. The availability of 51Cr-EDTA is limited, and all methods using radioactive tracers necessitate specific safety precautions. Serum- or plasma-based certified reference materials for iohexol and iothalamate and evidence-based protocols to accurately and robustly measure GFR (plasma vs. urinary clearance, single-sample vs. multiple-sample strategy, effect of sampling time delay) are lacking. This leads to substantial variation in reported mGFR results across studies and questions the scientific reliability of the alternative mGFR methods as the gold standard to evaluate kidney function. On top of the scientific discussion, regulatory issues are further narrowing the clinical use of mGFR methods. Therefore, this review is a call for standardization of mGFR in terms of three aspects: the marker, the analytical method to assess concentrations of that marker, and the procedure to determine GFR in practice. Moreover, there is also a need for an endogenous filtration marker or a panel of filtration markers from a single blood draw that would allow estimation of GFR as accurately as mGFR, and without the need for application of anthropometric, clinical, and demographic characteristics.

Midazolam and hydroxymidazolam plasma concentrations can be monitored with selected biochemical and physiological parameters of palliative care patients

RATIONALE & OBJECTIVE

Midazolam is one of top three drugs used in palliative care. Its use increases in the last days of hospice patients' lives while safe dosage can be challenging. Equations currently used to estimate glomerular filtration rate, e.g: the Cockroft-Gault (eGFR_CR) and the Modification of Diet in Renal Disease (eGFR_MDRD) ones, do not generate precise calculations, especially in palliative patients exhibiting variations in body parameters. Our aim was to seek new relationships between mean midazolam (M_avg) and alfahydroxymidazolam (OH-M_avg) concentrations in plasma, and selected biochemical and physiological parameters of palliative patients, to enable optimal midazolam pharmacotherapy.

STUDY DESIGN, PARTICIPANTS AND INTERVENTIONS

The pilot study included 11 Caucasians, aged 42-95, with advanced cancer disease, receiving midazolam in a hospice in-patient unit. We tested correlations among M_avg, BMI, eGFR_MDRD, midazolam clearance (CL), OH-M_avg, bilirubin (Bil) and blood creatinine concentration (Cr). F test and leave-one out (LOO) validation was applied to verify the correlations' significance and predictive ability.

RESULTS

We found ten statistically significant (p < 0.05) correlations related to midazolam pharmacokinetics and physiological factors. We formulated two equations with high degree of predictive ability, based on the eGFR_MDRD→CL and the (Bil + BMI × Ln(Cr))→M_avg-(OH-M_avg) correlations. The limitations of the study mainly revolve around its pilot nature and the need to continue testing the results on a bigger population. No funding to disclose.

CONCLUSIONS

The significance of correlations corresponding to the arithmetic expressions confirms that Bil, BMI, Ln(Cr) analyzed simultaneously report a series of processes on which midazolam metabolism depends. Two of ten correlations proposed came close to meet all LOO validation criteria. Current findings can help optimize midazolam treatment in palliative therapy.

Current Management of Patients With Acquired Solitary Kidney

Persons with acquired solitary kidney, including those who have had a unilateral nephrectomy for living kidney donation, renal malignancies, or trauma, have decreased renal mass that leads to increased intraglomerular pressure and glomerular hyperfiltration. These physiologic adaptations of solitary kidney may exacerbate other preexisting and genetic conditions that could create a predisposition to or worsen glomerular pathologies, leading to unfavorable renal outcomes. Hence, these persons may benefit from special care and lifestyle modifications, including nutritional interventions. There is a lack of consensus and evidence for proper surveillance and management after nephrectomy, and misconceptions in both directions of having a “normal” versus “abnormal” kidney status may cause confusion among patients and healthcare providers pertaining to long-term kidney health monitoring and management. We have reviewed available data on the impact of lifestyle modifications, particularly nutritional measures, and pharmacologic interventions, on short- and long-term outcomes after nephrectomy. We recommend avoidance of excessively high dietary protein intake (>1 g/kg per day) and high dietary sodium intake (>4 grams/d), adequate dietary fiber intake from plant-based foods, a target body mass index of <30 kg/m² (in non-athletes and non-bodybuilders), and judicious management of risk factors of progressive chronic kidney disease (CKD), and future studies should help to better determine optimal care practices for these persons.

Combination immunosuppressant therapy and lupus nephritis outcome: a hospital-based study

Lupus nephritis (LN) is the leading cause of mortality in lupus patients. This study aimed to investigate the treatment outcome and renal histological risk factors of LN in a tertiary referral center. Between 2006 and 2017, a retrospective observational study enrolled 148 biopsy-proven LN patients. After propensity score matching, 75 cases were included for further analysis. The classification and scoring of LN were assessed according to the International Society of Nephrology/Renal Pathology Society. Treatment response was evaluated by daily urine protein and urinalysis at two years after commencing induction treatment and the development of end-stage renal disease (ESRD). In total, 50.7% patients achieved complete remission (CR) or partial remission (PR), while 49.3% patients were categorized as nonresponders. Therapeutic responses in terms of CR/PR rates were associated with Systemic Lupus Erythematosus Disease Activity Index scores (odds ratio (OR): 1.34, 95% confidence interval (CI): 1.12-1.60, p = 0.001). Moreover, higher baseline creatinine levels (hazard ratio (HR): 2.10, 95% CI: 1.29-3.40, p = 0.003), higher renal activity index (HR: 1.30, 95% CI: 1.07-1.58, p = 0.008) and chronicity index (HR: 1.40, 95% CI: 1.06-1.85, p = 0.017) predicted ESRD. Among pathological scores, cellular crescents (HR: 4.42, 95% CI: 1.01-19.38, p = 0.049) and fibrous crescents (HR: 5.93, 95% CI: 1.41-24.92, p = 0.015) were independent risk factors for ESRD. In conclusion, higher lupus activity was a good prognostic marker for renal remission. Renal histology was predictive of ESRD. Large-scale prospective studies are required to verify the efficacy of mycophenolate in combination with azathioprine or cyclosporine in LN patients.

Estimation of glomerular filtration rate in patients with systemic lupus erythematosus

The objective of this study was to compare the limit of agreement of creatinine clearance (CrCl) estimated by different equations with the CrCl measured by 24-hour urine collection in Hong Kong Chinese patients with systemic lupus erythematosus (SLE). Forty-three SLE patients with mild to moderate renal impairment (serum creatinine concentration 80 mol/L to 300 mol/L for females; and 106 mol/L to 300 mol/L for males) and not requiring renal replacement therapy were assessed. The estimated clearances were calculated by the Cockcroft-Gault (CG) equation, the Modification of Diet in Renal Disease (MDRD) study equation and the abbreviated MDRD (aMDRD) study equation. The estimated clearances were compared against the measured CrCl by 24- hour urine collection for their limit of agreement. Forty-three patients with mean (SD) age of 41.6 (8.4) years were assessed. As compared to the measured CrCl in patients with SLE, the clearances by CG equation, MDRD and aMDRD equations predicted a mean difference of 0.8% (95% confidence interval, 43.9-42.3%); 8.6% (95% CI, 24.3-7.2%) and 4.7% (95% CI, 21.4-12%), respectively. There is a tendency for the MDRD and aMDRD study equations to underestimate CrCl. The MDRD and aMDRD study equations have better predictive value than the CG equation.

Measuring GFR: a systematic review

BACKGROUND

No comprehensive systematic review of the accuracy of glomerular filtration rate (GFR) measurement methods using renal inulin clearance as reference has been published.

STUDY DESIGN

Systematic review with meta-analysis of cross-sectional diagnostic studies.

SETTING & POPULATION

Published original studies and systematic reviews in any population.

SELECTION CRITERIA FOR STUDIES

Index and reference measurements conducted within 48 hours; at least 15 participants studied; GFR markers measured in plasma or urine; plasma clearance calculation algorithm verified in another study; tubular secretion of creatinine had not been blocked by medicines.

INDEX TESTS

Endogenous creatinine clearance; renal or plasma clearance of chromium 51-labeled ethylenediaminetetraacetic acid (51Cr-EDTA), diethylenetriaminepentaacetic acid (DTPA), iohexol, and iothalamate; and plasma clearance of inulin.

REFERENCE TEST

Renal inulin clearance measured under continuous inulin infusion and urine collection.

RESULTS

Mean bias <10%, median bias <5%, the proportion of errors in the index measurements that did not exceed 30% (P30) ≥80%, and P10 ≥50% were set as requirements for sufficient accuracy. Based on the GRADE (Grading of Recommendations Assessment, Development and Evaluation) approach, the quality of evidence across studies was rated for each index method. Renal clearance of iothalamate measured GFR with sufficient accuracy (strong evidence). Renal and plasma clearance of 51Cr-EDTA and plasma clearance of iohexol were sufficiently accurate to measure GFR (moderately strong evidence). Renal clearance of DTPA, renal clearance of iohexol, and plasma clearance of inulin had sufficient accuracy (limited evidence). Endogenous creatinine clearance was an inaccurate method (strong evidence), as was plasma clearance of DTPA (limited evidence). The evidence to determine the accuracy of plasma iothalamate clearance was insufficient. With the exception of plasma clearance of inulin, only renal clearance methods had P30 >90%.

LIMITATIONS

The included studies were few and most were old and small, which may limit generalizability. Requirements for sufficient accuracy may depend on clinical setting.

CONCLUSIONS

At least moderately strong evidence suggests that renal clearance of 51Cr-EDTA or iothalamate and plasma clearance of 51Cr-EDTA or iohexol are sufficiently accurate methods to measure GFR.

Comparison of creatinine clearance estimates with routine measured clearance in adult Jordanians with a kidney transplant

OBJECTIVES

There are conflicting data on using the Cockroft-Gault formula and the Modification of Diet in Renal Disease formula to assess graft function in kidney transplants. This study uses a cohort of Jordanian kidney transplant patients to assess performance of the Cockroft-Gault formula and the Modification of Diet in Renal Disease equations by using the criterion standard of measured creatinine clearance.

MATERIALS AND METHODS

Creatinine clearance measured by 24-hour urine creatinine in patients with a kidney transplant was compared with the estimated clearance using the Cockroft-Gault formula and the Modification of Diet in Renal Disease equations. Correlation, limits of agreement, and concordance analyses were used.

RESULTS

There was a positive correlation between both the Cockcroft-Gault (r=0.878; P < .001) and the Modification of Diet in Renal Disease (r=0.732; P < .001) equations with creatinine clearance. The former was statistically superior (P = .0416). Using Bland-Altman plots, the limits of agreement were wide for both methods. After log transformation, the limits of agreement were -0.06 to +0.27 for the Cockcroft-Gault formula, and -0.21 to + 0.26 for the Modification of Diet in Renal Disease. Concordance analyses showed a correlation coefficient of 0.7384 (95% CI: 0.6134 to 0.8273) when the Cockcroft-Gault formula was used, and 0.7257 (95% CI: 0.5622 to 0.8345) for the Modification of Diet in Renal Disease. Pearson P coefficient (precision) and bias correction factor Cb (accuracy) for the Cockcroft-Gault formula and for the Modification of Diet in Renal Disease were 0.8762, 0.8427, 0.7324, and 0.9908.

CONCLUSIONS

In Jordanian patients with a renal transplant, although the Cockcroft-Gault formula performed slightly better than the Modification of Diet in Renal Disease equation in estimating creatinine clearance, neither of these equations can accurately predict renal graft function.

Joint European League Against Rheumatism and European Renal Association-European Dialysis and Transplant Association (EULAR/ERA-EDTA) recommendations for the management of adult and paediatric lupus nephritis

OBJECTIVES

To develop recommendations for the management of adult and paediatric lupus nephritis (LN).

METHODS

The available evidence was systematically reviewed using the PubMed database. A modified Delphi method was used to compile questions, elicit expert opinions and reach consensus.

RESULTS

Immunosuppressive treatment should be guided by renal biopsy, and aiming for complete renal response (proteinuria <0.5 g/24 h with normal or near-normal renal function). Hydroxychloroquine is recommended for all patients with LN. Because of a more favourable efficacy/toxicity ratio, as initial treatment for patients with class III-IV(A) or (A/C) (±V) LN according to the International Society of Nephrology/Renal Pathology Society 2003 classification, mycophenolic acid (MPA) or low-dose intravenous cyclophosphamide (CY) in combination with glucocorticoids is recommended. In patients with adverse clinical or histological features, CY can be prescribed at higher doses, while azathioprine is an alternative for milder cases. For pure class V LN with nephrotic-range proteinuria, MPA in combination with oral glucocorticoids is recommended as initial treatment. In patients improving after initial treatment, subsequent immunosuppression with MPA or azathioprine is recommended for at least 3 years; in such cases, initial treatment with MPA should be followed by MPA. For MPA or CY failures, switching to the other agent, or to rituximab, is the suggested course of action. In anticipation of pregnancy, patients should be switched to appropriate medications without reducing the intensity of treatment. There is no evidence to suggest that management of LN should differ in children versus adults.

CONCLUSIONS

Recommendations for the management of LN were developed using an evidence-based approach followed by expert consensus.

New biomarkers of acute kidney injury and the cardio-renal syndrome

Changes in renal function are one of the most common manifestations of severe illness. There is a clinical need to intervene early with proven treatments in patients with potentially deleterious changes in renal function. Unfortunately progress has been hindered by poor definitions of renal dysfunction and a lack of early biomarkers of renal injury. In recent years, the definitional problem has been addressed with the establishment of a new well-defined diagnostic entity, acute kidney injury (AKI), which encompasses the wide spectrum of kidney dysfunction, together with clearer definition and sub-classification of the cardio-renal syndromes. From the laboratory have emerged new biomarkers which allow early detection of AKI, including neutrophil gelatinase-associated lipocalin (NGAL) and cystatin C. This review describes the new concepts of AKI and the cardio-renal syndromes as well as novel biomarkers which allow early detection of AKI. Panels of AKI biomarker tests are likely to revolutionise the diagnosis and management of critically ill patients in the coming years. Earlier diagnosis and intervention should significantly reduce the morbidity and mortality associated with acute kidney damage.

Prevention of chronic kidney disease in spina bifida

OBJECTIVE

The prevalence of progressive chronic kidney disease (CKD) in children and adults with spina bifida is considerable, rising, and entirely preventable.

REMOVING THE CAUSE

PREVENTION OF SPINA BIFIDA: The best prevention of CKD in spina bifida is prevention of spina bifida itself through strategies that include folate supplementation, ideally before pregnancy.

THE CAUSE OF CKD

Dysfunctional bladder outlet causes febrile Urinary Tract Infections (UTI), even with clean intermittent catheterization (CIC), and subsequent renal scarring. The development of secondary vesicoureteric reflux (VUR) increases the risk of renal scarring and CKD.

FINDING THE IDEAL MARKER FOR MEASUREMENT OF RENAL FUNCTION IN SPINA BIFIDA

Creatinine-based methods are insensitive because of low muscle mass and underdeveloped musculature in the legs. Only Cystatin C-based eGFR can reliably assess global renal function in these patients. However, unilateral renal damage requires nuclear medicine scans, such as (99m)Tc DMSA. (VIDEO)URODYNAMICS STUDIES (UDS): Early treatment is recommended based on UDS with anticholinergics, CIC, and antibiotic prophylaxis when indicated. Overnight catheter drainage, Botox, and eventually augmentation cystoplasty are required for poorly compliant bladders. A continent child or one rendered continent following surgery is at a higher risk of renal damage.

CONCLUSION

A multidisciplinary approach is required to reduce the burden of CKD in patients with spina bifida. The right tools have to be utilized to monitor these patients, particularly if recurrent UTIs occur. Cystatin C eGFR is preferred for monitoring renal damage in these patients, and (99m)Tc DMSA scans have to be used to detect unilateral renal scarring.

MDRD or CKD-EPI study equations for estimating prevalence of stage 3 CKD in epidemiological studies: which difference? Is this difference relevant?

BACKGROUND

Prevalence of stage 3 chronic kidney disease (CKD) is increasing according to the NHANES study. Prevalence has been calculated using the MDRD study equation for estimating glomerular filtration rate (GFR). Recently, a new estimator based on creatinine, the CKD-EPI equation, has been proposed which is presumed to better perform in normal GFR ranges. The aim of the study was to measure the difference in prevalence of stage 3 CKD in a population using either the MDRD or the CKD-EPI study equations.

METHODS

CKD screening is organized in the Province of Liège, Belgium. On a voluntary basis, people aged between 45 and 75 years are invited to be screened. GFR is estimated by the MDRD study equation and by the "new" CKD-EPI equations.

RESULTS

The population screened consisted in 1992 people (47% of men). Mean serum creatinine was 0.86 +/- 0.20 mg/dL. The prevalence of stage 3 CKD in this population using the MDRD or the CKD-EPI equations was 11.04 and 7.98%, respectively. The prevalence of stage 3 CKD is significantly higher with the MDRD study equation (p < 0,0012).

CONCLUSIONS

Prevalence of stage 3 CKD varies strongly following the method used for estimating GFR, MDRD or CKD-EPI study equations. Such discrepancies are of importance and must be confirmed and explained by additional studies using GFR measured with a reference method.

eGFR is a reliable preoperative renal function parameter in patients with gastric cancer

AIM: To evaluate the validity of the estimated glomerular filtration rate (eGFR) as a preoperative renal function parameter in patients with gastric cancer.

METHODS: A retrospective study was conducted in 147 patients with gastric cancer. Preoperative creatinine clearance (Ccr), eGFR, and pre- and postoperative serum creatinine (sCr) data were examined. Preoperative Ccr and eGFR were then compared for their reliability in predicting postoperative renal dysfunction.

RESULTS: Among 110 patients with normal preoperative Ccr values, 7 (6.3%) had abnormal postoperative sCr values, and among 112 patients with normal preoperative eGFR values, postoperative sCr was abnormal in 5 (4.5%) (P = 0.53). Among 37 patients with abnormal preoperative Ccr values, 30 (81.1%) had normal postoperative sCr values, and of 35 patients with abnormal preoperative eGFR values, postoperative sCr was normal in 25 (71.4%) (P = 0.34). Preoperative Ccr was significantly correlated with eGFR (r = 0.514), and postoperative sCr was significantly correlated with preoperative Ccr (r = -0.334) and eGFR (r = -0.02).

CONCLUSION: Preoperative eGFR is as effective as Ccr for predicting postoperative renal dysfunction. eGFR should therefore be used as an indicator of preoperative renal function in place of Ccr since it is a cheaper and easier to perform test.

Measured GFR as a confirmatory test for estimated GFR

Clinical assessment of kidney function is central to the practice of medicine. GFR is widely accepted as the best index of kidney function in health and disease, and accurate values are required for optimal decision making. Estimated GFR based on serum creatinine is now widely reported by clinical laboratories, and in most circumstances, estimated GFR is sufficient for clinical decision making. GFR estimates may be inaccurate in the non-steady state and in people in whom non-GFR determinants differ greatly from those in whom the estimating equation was developed. If GFR estimates are likely inaccurate or if decisions based on inaccurate estimates may have adverse consequences, a measured GFR is an important confirmatory test. Endogenous creatinine clearance is the most common method used to measure GFR in clinical practice but may be difficult to obtain or fraught with error. We review methods for GFR measurement using urinary and plasma clearance of exogenous filtration markers and focus on urinary clearance of iothalamate and plasma clearance of iohexol compared with inulin clearance. We suggest plasma clearance of nonradioactive markers be more widely implemented in clinical settings. Further research is necessary on the impact of the use of measured GFR as a confirmatory test.

For estimating creatinine clearance measuring muscle mass gives better results than those based on demographics

Estimation of creatinine clearance requires knowledge of creatinine generation which can vary in different groups of patients. Since the main source of creatinine is muscle we used dual-energy X-ray absorptiometry to measure the mass of muscle in a cohort of adult men and women in Rochester, Minnesota. Serum and 24 h urinary creatinines were measured directly. The urinary creatinine was estimated using equations based on age and gender and muscle mass in order to calculate creatinine clearance. Among 664 subjects with a mean age of 55+/-20 years, 51% of whom were women, the model fit for urinary creatinine estimated with age and gender (R2=0.359) was similar to that estimated with measured muscle mass (R2=0.359). The likelihood of chronic kidney disease (creatinine clearance of less than 60 ml/min per 1.73 m2) in older subjects was highest with equations that used age, and likelihood of CKD in women was highest with equations that used gender. The outcomes of mortality and cardiovascular disease had stronger associations with decreased creatinine clearance calculated with age and gender than by the clearance calculated with muscle mass. This could be explained by age being a potent predictor of mortality and cardiovascular disease independent of urinary creatinine, muscle mass, and gender. Our study shows that the likelihood of chronic kidney disease in the elderly and in women and the risk of adverse outcomes may be inflated by equations that use patient demographics to estimate creatinine generation.

Estimating glomerular filtration rate: Cockcroft-Gault and Modification of Diet in Renal Disease formulas compared to renal inulin clearance

BACKGROUND AND OBJECTIVES

Evaluation of renal function by estimation of the glomerular filtration rate (GFR) is very important for the diagnosis and treatment of patients with chronic kidney disease (CKD). The Cockcroft-Gault (CG) and Modification of Diet in Renal Disease (MDRD) formulas are the most commonly used estimations.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Estimated GFR values by each formula were compared with measured GFR (mGFR) by renal inulin clearance in 2208 European adults (46% women, 1.4% Caribbean blacks), with and without CKD, and mean mGFR 72.4 +/- 39.0 (range 2.2 to 177.2) ml/min/1.73 m(2).

RESULTS

Overall, the CG and MDRD formulas showed bias (mean difference) -3.5 ml/min/1.73 m(2) (5.3%), P < 0.001, and -9.8 ml/min/1.73 m(2) (-6.4%), P < 0.001; precision (SD of bias) 21.5 ml/min/1.73 m(2) (43.1%) and 20.0 ml/min/1.73 m(2) (33.0%); limits of agreement (2 SD by Bland-Altman method) 39.5 to -46.5 (range 86.0) ml/min/1.73 m(2) and 30.2 to -49.8 (range 80.0) ml/min/1.73 m(2); and accuracy within +/-30% of mGFR 70.8 and 69.0%, respectively. Both formulas showed a trend for decreasing accuracy with lower mGFR levels. According to the Kidney Disease Outcomes Quality Initiative (K/DOQI)-CKD classification's five GFR groups, the CG and MDRD formulas properly assigned 61.6 and 57.1% of the entire population and had a range of positive predictive values 42.6 to 81.8% and 39.6 to 85.2% and of negative predictive values 81.7 to 96.6% and 76.4 to 97.5%, respectively.

CONCLUSIONS

The CG and MDRD formulas had some limitations for proper GFR estimation and K/DOQI-CKD classification by GFR levels alone.

Estimating renal function in lupus nephritis: comparison of the Modification of Diet in Renal Disease and Cockcroft Gault equations

Estimates of renal function are widely used in clinical practice and research. We assessed the performance of the Cockcroft-Gault (CG) and the Modification of Diet in Renal Disease (MDRD) equations in lupus nephritis patients. Data from ninety-seven lupus nephritis patients in the Hopkins Lupus Cohort were reviewed. Two renal function estimates, the CG and the MDRD, were compared with the 24 h creatinine clearance (CrCl). In the entire group of patients, the CG and MDRD equations had good global agreement with CrCl (R-square = 0.91 and 0.69, respectively). On average the CG equation overestimated CrCl by 2.36 mL/min/1.73 m(2), whereas the MDRD equation underestimated CrCl by 5.85 mL/min/1.73 m(2), P = 0.0004. The CG equation had greater accuracy (mean squared error) than the MDRD equation (14.93 versus 28.47 mL/min/1.73 m(2), P = 0.002) when predicting CrCl. Although both equations lacked precision (standard deviation of the difference scores) in patients with CrCl > or = 60 mL/min/1.73 m(2), the CG equation was more precise than the MDRD equation in this group, (15.68 versus 29.58 mL/min/1.73 m(2), P = 0.003). In lupus nephritis patients, the CG equation was superior to the MDRD equation as an estimate of CrCl. However, both equations lacked precision in patients with CrCl > or = 60 mL/min/1.73 m(2).

Improved GFR estimation by combined creatinine and cystatin C measurements

Plasma creatinine may not reflect glomerular filtration rate (GFR) especially in the early stages of chronic kidney disease (CKD). Plasma cystatin C (cysC), however, has the potential to more accurately determine early GFR reduction. We sought to improve the creatinine-based GFR estimation by including cysC measurements. We derived a reference GFR from standard dual plasma sampling (99m)Tc-DTPA clearance in a training cohort of 376 randomly selected adult Chinese patients with CKD. We compared reference values to estimated GFR and applied multiple regression models to one equation based solely on cysC, and to another combining plasma creatinine (Pcr) and cysC measurements of the training cohort. The results were validated by testing an additional 191 patients. The difference, precision, and accuracy of the two estimates were compared with the modified Modification of Diet in Renal Disease (MDRD) equation for Chinese patients, and another estimate combining cysC and modified MDRD calculations. The estimated GFR combining Pcr and cysC measurements more accurately matched the reference GFR at all stages of CKD than the other equations, particularly in patients with near-normal kidney function.

Understanding estimated glomerular filtration rate: implications for identifying chronic kidney disease

PURPOSE OF REVIEW

Glomerular filtration rate (GFR) can be estimated using serum markers such as serum creatinine (SCr) or cystatin C. This review presents new insights into estimated GFR based on theory, validation studies, SCr assay standardization, cystatin C, and longitudinal comparison with measured GFR.

RECENT FINDINGS

The estimation of GFR by SCr differs in health and in chronic kidney disease (CKD) due to differences in GFR range and in creatinine production between these two populations. Among populations with normal baseline GFR, there is a more rapid decline in measured GFR than in SCr-based estimated GFR. While elevated SCr is specific for CKD, other disease processes may lead to elevated cystatin C. Validation is improved by refitting equation coefficients to compare populations, recognizing the asymmetry between estimated GFR and measured GFR, and using residual plots instead of Bland-Altman plots to assess bias.

SUMMARY

As a screening test, SCr should be interpreted as a marker of CKD probability in the context of the patient's clinical presentation. Measured GFR or creatinine clearance may be helpful in high-risk patients with normal SCr levels. GFR estimating equations should be reserved for patients with identified CKD. Standardized SCr and cystatin C assays are needed.

Lupus Nephritis

Lupus nephritis is one of the more serious manifestations of the systemic autoimmune disease, systemic lupus erythematosus, and is associated with considerable morbidity and even mortality. Treatment remains problematic, particularly in terms of controlling the underlying disease process while at the same time preventing unacceptable side effects of therapy. In recent years, clinical trials have started to define optimum regimens of the immunosuppressive agents presently in use. The etiology and pathogenesis of systemic lupus erythematosus and lupus nephritis still are understood incompletely. Nevertheless, insights gained from basic science research in both animals and human beings now are being translated into newer therapies that have the potential to be safer and more specific than those currently available.

Comparison of methods for determining renal function decline in early autosomal dominant polycystic kidney disease: the consortium of radiologic imaging studies of polycystic kidney disease cohort

A decline in renal function suggests progression of chronic kidney disease. This can be determined by measured GFR (e.g., iothalamate clearance), serum creatinine (SCr)-based GFR estimates, or creatinine clearance. A cohort of 234 patients with autosomal dominant polycystic kidney disease and baseline creatinine clearance>70 ml/min were followed annually for four visits. Iothalamate clearance, SCr, and creatinine clearance were obtained at each visit. Estimated GFR (eGFR) was determined with the Modification of Diet in Renal Disease (MDRD) and Cockcroft-Gault equations. Renal function slopes had a mean residual SD of 10.7% by iothalamate clearance, 8.2% by MDRD equation, 7.7% by Cockcroft-Gault equation, and 14.8% by creatinine clearance. By each method, a decline in renal function (lowest quintile slope) was compared among baseline predictors. Hypertension was associated with a decline in iothalamate clearance (odds ratio [OR] 5.8; 95% confidence interval [CI] 2.3 to 14), eGFR (OR [MDRD] 2.0 [95% CI 1.0 to 4.2] or OR [Cockcroft-Gault] 1.9 [95% CI 0.9 to 3.9]), and creatinine clearance (OR 2.0; 95% CI 1.0 to 4.2). Each doubling of kidney volume at baseline was associated with a decline in iothalamate clearance (OR 2.4; 95% CI 1.5 to 3.7), eGFR (OR 1.7 [95% CI 1.1 to 2.6] or 2.1 [95% CI 1.4 to 3.3]), and creatinine clearance (OR 1.7; 95% CI 1.1 to 2.5). Predictor associations were strongest with measured GFR. Misclassification from changes in non-GFR factors (e.g., creatinine production, tubular secretion) conservatively biased associations with eGFR. Misclassification from method imprecision attenuated associations with creatinine clearance.

Application of GFR-estimating equations in Chinese patients with chronic kidney disease

BACKGROUND

To evaluate whether the Modification of Diet in Renal Disease (MDRD) equations could be applied accurately to Chinese patients with chronic kidney disease (CKD), glomerular filtration rates (GFRs) estimated by using MDRD equation 7 (7GFR), the abbreviated MDRD equation (aGFR), and the Cockcroft-Gault equation (cGFR) were compared in patients with different stages of CKD.

METHODS

The study enrolled patients with CKD diagnosed according to the National Kidney Foundation-Kidney Disease Outcomes Quality Initiative guidelines. All patients were older than 18 years and without acute renal function deterioration, edema, skeletal muscle atrophy, or amputation. Sex, age, body height, and body weight were recorded, and plasma creatinine levels were measured by means of Jaffe's kinetic method using a Hitachi 7600 analyzer (Hitachi, Tokyo, Japan; reagents from Roche Diagnostics, Mannheim, Germany). Creatinine, urea, and albumin were measured in a single clinical laboratory. Dual plasma sampling of technetium Tc 99m-labeled diethylene triamine pentaacetic acid plasma clearance was used as the reference standard GFR (sGFR) for comparison of 7GFRs, aGFRs, and cGFRs at different stages of CKD.

RESULTS

The study enrolled 261 patients, including 146 men and 115 women. Causes of CKD included primary or secondary glomerular disease, obstructive kidney disease, chronic tubulointerstitial disease, and others. Values for 7GFR, aGFR, and cGFR were significantly greater than for sGFR in patients with CKD stages 4 to 5 (the lower the sGFR, the greater the difference); whereas 7GFR, aGFR, and cGFR were significantly lower than sGFR in patients with CKD stage 1.

CONCLUSION

Our results show that in a Chinese population with CKD, MDRD equation 7 and the abbreviated MDRD equation overestimated GFR in patients with CKD stages 4 to 5 and underestimated GFR in those with CKD stage 1. These results indicate that careful modification of these equations may be necessary in Chinese populations with CKD.

Validation of the Modification of Diet in Renal Disease formula for estimating GFR with special emphasis on calibration of the serum creatinine assay

BACKGROUND

The Modification of Diet in Renal Disease (MDRD) formula is recommended by European and American guidelines for estimating glomerular filtration rate (GFR). However, the accuracy of the formula has been questioned in several studies. Our objective is to evaluate the performance of the MDRD formula with special emphasis on the possibility that interlaboratory calibration differences for serum creatinine reduce the accuracy of the formula.

METHODS

The MDRD and 7 other commonly used formulae were evaluated regarding bias, precision, and accuracy. The 215 adults included were patients with chronic kidney disease, potential kidney donors, and patients referred before nephrotoxic chemotherapy. Serum creatinine was measured by means of a kinetic Jaffé method (Hitachi 917, Hitachi, Tokyo, Japan; reagents from Roche Diagnostics, Mannheim, Germany). GFR, measured as plasma clearance of chromium 51-labeled EDTA (Cr-EDTA), ranged from 3 to 162 mL/min/1.73 m2.

RESULTS

The MDRD formula was heavily biased, but it still had significantly better accuracy than the other formulae tested. After recalibrating our serum creatinine values (serum creatinine [mg/dL] = -0.215 + 1.08 * serum creatinine), systematic bias was greatly reduced and better accuracy was achieved: 45.6% of results differed less than 15% from Cr-EDTA, 64.2% differed less than 30%, and 81.4% differed less than 50%. The equation for recalibrating creatinine values was based on data with traceability to reference methods and on sensitivity analysis.

CONCLUSION

The MDRD formula seems to be the best formula available for GFR estimating, but it is based on a serum creatinine method calibrated to give much lower values than most laboratories, leading to underestimation of GFR in mild renal insufficiency.

Induction of tolerance in autoimmune diseases by hematopoietic stem cell transplantation: getting closer to a cure?

Hematopoietic stem cells (HSCs) are the earliest cells of the immune system, giving rise to B and T lymphocytes, monocytes, tissue macrophages, and dendritic cells. In animal models, adoptive transfer of HSCs, depending on circumstances, may cause, prevent, or cure autoimmune diseases. Clinical trials have reported early remission of otherwise refractory autoimmune disorders after either autologous or allogeneic hematopoietic stem cell transplantation (HSCT). By percentage of transplantations performed, autoimmune diseases are the most rapidly expanding indication for stem cell transplantation. Although numerous editorials or commentaries have been previously published, no prior review has focused on the immunology of transplantation tolerance or development of phase 3 autoimmune HSCT trials. Results from current trials suggest that mobilization of HSCs, conditioning regimen, eligibility and exclusion criteria, toxicity, outcome, source of stem cells, and posttransplantation follow-up need to be disease specific. HSCT-induced remission of an autoimmune disease allows for a prospective analysis of events involved in immune tolerance not available in cross-sectional studies.

Reappraisal of serum beta2-microglobulin as marker of GFR

INTRODUCTION

Beta 2 microglobulin (beta2M) is filtered by the glomeruli and reabsorbed by the proximal tubular cells where it is metabolized. Its plasma concentration increases with decreasing renal function.

AIM

To compare serum creatinine (Cr) and serum beta2M as markers of GFR.

PATIENTS AND METHODS

In 160 adult patients, with various kidney diseases and different GFR, serum Cr (autoanalyzer), serum beta2M (RIA) and GFR (bladder cumulative method using 99mTc-DTPA as glomerular tracer) were measured in the same day.

RESULTS

A linear relationship was observed between In GFR and both In serum Cr (lnCr=3.112-0.716 lnGFR; r=0.92) and ln serum beta2M (lnbeta2M= 4.274-0.814 lnGFR; r = 0.90). With decreasing GFR the increase in serum beta2M was higher than that of serum Cr (see regression coefficients that are significantly different). The normal upper limit of serum Cr corresponds to a GFR 48.1 mL/min while that of serum beta2M to a GFR 65.0. With decreasing GFR the increase of serum beta2M occurs before than that of serum Cr.

CONCLUSIONS

With declining renal function, serum beta2M increases more and before than serum Cr. Serum beta2M is a good endogenous marker of GFR, better than serum Cr.

Intense immune suppression for systemic lupus--the role of hematopoietic stem cells

The treatment of severe autoimmune diseases has been recently revitalized by the introduction of intense immune suppression with immune ablative intent followed by three different procedures. These are allogeneic hematopoietic stem cell transplantation (HSCT), autologous HSCT (using either marrow or peripheral blood), and intense immune suppression without stem cell support. Current trials suggest that high dose immune suppressive therapy with or without autologous hematopoietic stem cell support can induce remission of previously refractory disease. Follow-up is too brief to determine if intense immune suppression, and more specifically autologous HSCT, will ultimately cure SLE. It is conceivable that an allogeneic source of stem cells from a normal donor (e.g. HLA matched sibling) will be required to achieve a cure. It is also possible that autologous HSCT, even if not curative, may prolong the life of patients with otherwise high-risk features. In carefully selected patients, the potential benefits of this procedure may outweigh the risks.

Validity of a vasculitis activity index for systemic necrotizing vasculitis

OBJECTIVE

To establish the validity of an index designed to measure activity in systemic necrotizing vasculitis (SNV).

METHODS

The Vasculitis Activity Index (VAI) was designed to incorporate appropriately weighted clinical measurements that reflect disease activity in SNV. We performed a pilot study to guide the modification and subsequent testing of the initial design. The data necessary to calculate the VAI are direct ratings by a clinical observer of the degree of activity in 9 organ systems and 3 indirect measures of vasculitis activity. These data are recorded on 0-4 visual analog scales. Physician's global assessment (PGA) is used as the "gold standard" measurement of disease activity. The VAI was validated using 2 independent data sets: the questionnaire data set, derived from test case histories ("paper cases") sent to 100 practicing rheumatologists, and the clinic data set, obtained from use of the VAI in 204 regular care visits of 74 patients with SNV.

RESULTS

The VAI correlated highly with the PGA: Pearson's correlation coefficient R = 0.84 (95% confidence interval [95% CI] 0.80-0.88) for the questionnaire data set, and R = 0.92 (95% CI 0.90-0.94) for the clinic data set. The mean of the interobserver coefficients of variation for the test case histories was lower for the VAI than for the PGA (mean difference 0.45; P = 0.002), indicating that the VAI has less interobserver variation than does the PGA. The change in VAI between clinic visits for individual patients correlated highly with the change in PGA (R = 0.88, 95% CI = 0.83-0.91). The VAI data collection form requires about 1 minute to complete, including computation of the score.

CONCLUSION

The VAI is a valid measure of vasculitis activity that correlates highly with the PGA. In addition, the VAI has less interobserver variation than the PGA and has a high level of sensitivity to change over time. Additional testing of the VAI appears warranted.

Renal haemodynamic characteristics in patients with lupus nephritis

OBJECTIVE

To clarify the characteristics of renal haemodynamics in patients with lupus nephritis (LN).

METHODS

The glomerular filtration rate (GFR) and renal plasma flow (RPF) of 37 patients with active LN were studied longitudinally over an interval of 8 to 144 weeks during treatment with corticosteroids or cytotoxic drugs, or both. All patients had clinical renal disorders and underwent renal biopsies.

RESULTS

Analysis of renal biopsy specimens showed that 31 patients had class IV LN. Class II, III, and VLN were present in two patients each. The average GFR increased significantly from 65.4 (SD 33.0) in the pretreatment stage to 86.6 (31.6) ml/min in the post-treatment stage, accompanied by an improvement in urinary or immunological abnormalities, or both. On the other hand, RPF decreased significantly from 625.2 (243.0) to 519.8 (179.0) ml/min. Therefore, the filtration fraction (FF) increased significantly from 10.7 (4.3)% to 16.8 (3.7)%. Low FF was recognised predominantly in patients with class IV LN, but was also observed in patients with other classes. The FF returned towards normal irrespective of the degree of GFR recovery. No significant changes were observed in the levels of blood pressure.

CONCLUSION

A reduction in GFR out of proportion to the reduction in RPF as demonstrated by the low FF values was related to the severity of LN or disease activity, or both. Therefore, relative evaluation of GFR and RPF, namely the determination of FF, may be a useful clinical parameter to determine the status of LN.

Role of nutrition in prevention of the progression of renal disease

In rats with renal disease, low-protein diets slow the decline in renal function, histologic damage, and mortality. Low-protein (and phosphorus) diets can also ameliorate uremic symptoms, secondary hyperparathyroidism, and metabolic acidosis in patients with chronic renal failure. Albeit controversial, evidence also suggests that dietary protein restriction can slow the rate of progression of renal failure and the time until end-stage renal failure. These dietary regimens appear to be safe and patients with chronic renal failure are able to activate normal compensatory mechanisms designed to conserve lean body mass when dietary protein intake is restricted. When low-protein diets are prescribed, patients should be closely monitored to assess dietary compliance and to ensure nutritional adequacy. Evidence that the spontaneous intake of dietary protein decreases in patients with progressive chronic renal failure who consume unrestricted diets should not be construed as an argument against the use of low-protein diets. Rather, it is a persuasive argument to restrict dietary protein intake in order to minimize complications of renal failure while preserving nutritional status.

Extended measurement of glomerular filtration rate and effective renal plasma flow in ambulatory patients

We describe a standardized clearance method over 5 h (one hour equilibration followed by eight consecutive 30 min clearance periods [period 2-9]) for the estimation of GFR (iothalamate I125) and ERPF (hippuran I131) during water diuresis in ambulatory and exercising patients. Four groups were examined. In group I (normal controls, n = 15) there were no significant changes in GFR, ERPF and FF (P > 0.10) during repeated clearance periods (mean of period 2-5 versus period 6-9). The reproducibility of the method was studied at a mean interval of 3.7 weeks in a group of patients with stable reduction of GFR (group II, n = 7). The values for GFR, ERPF, FF and RVR did not change significantly in this group, and correlated significantly between repeated studies (r = 0.81 to r = 0.99). In group III (untreated hypertensive patients with reduced GFR, n = 13) there was a time dependent 7.2% decrease in GFR (P < 0.05), significantly different from group I (P < 0.02), a 10.0% decrease in ERPF (P < 0.01) and no significant change in FF (P = 0.08) when the mean of period 2-5 was compared with the mean of period 6-9. In healthy controls (group IV, n = 8) light sustained bicycle exercise (25 W) induced a 7.1% decline in GFR (P < 0.01), 17.4% decline in ERPF (P < 0.001) and a 13.6% increase in FF (P < 0.001). We conclude that ambulatory measurements of GFR and RPF can be carried out over a period of 5 h with satisfactory precision and repeatability. Ambulatory hypertensive patients with moderately reduced GFR showed the same degree of time dependent downward drift of GFR and ERPF without exercise as was seen in healthy individuals during light exercise. Accordingly, in these groups single clearance periods imply a risk for under or overestimation of renal function, and time controls are necessary during clearance studies.

Assessing the effectiveness of therapy to prevent the progression of renal disease

Most studies of progressive renal disease assess the effectiveness of therapy from sequential measurements of renal excretory function, such as glomerular filtration rate, creatinine clearance, and serum creatinine concentration. This review summarizes the strengths and limitations of these measurements and proposes guidelines for selecting the outcome measure in clinical trials. In addition, this review examines certain issues related to the design and interpretation of studies on the progression of renal disease. Although this work primarily addresses issues relevant to clinical trials, the principles involved are relevant to the assessment of renal function in clinical settings as well.

Creatinine clearance during cimetidine administration for measurement of glomerular filtration rate

Creatinine clearance inaccurately estimates true glomerular filtration rate (GFR) because of tubular secretion of creatinine. We studied the ability of oral cimetidine, a blocker of tubular creatinine secretion, to improve the accuracy of measuring creatinine clearance. Clearances of inulin and endogenous creatinine were simultaneously measured in 16 patients with renal disease before administration of cimetidine and during 8 successive 3 h clearance periods with cimetidine 400 mg as priming dose followed by 200 mg every 3 h. At baseline, creatinine relative to inulin clearance (ClC/Cll) ranged from 1.14 to 2.27. With cimetidine, ClC/Cll approached unity in 8 patients (mean 1.02 [SD 0.03]), but considerably exceeded unity in 8 others (1.33 [0.14]). Plasma cimetidine/creatinine ratio was smaller in this second group, due to significantly higher renal clearance of cimetidine (333 [136] vs 165 [89] ml/min, p = 0.01). In a further study, cimetidine dose and, consequently plasma cimetidine concentration, was increased in 6 additional patients who had incomplete inhibited previously. This increased dose completely inhibited tubular creatinine secretion in the third until the sixth hour, so that creatinine clearance equalled GFR. Provided an adequate dose of cimetidine is given, 24 h creatinine clearance during administration of drug measures GFR accurately in patients with renal disease. However, because of the maximum daily dose of cimetidine that is advised, short clearance times (3 h) are recommended.

Cimetidine improves the reliability of creatinine as a marker of glomerular filtration

To investigate whether the administration of cimetidine can improve the reliability of creatinine as a marker of GFR, we compared the creatinine clearance (CCr) to the clearance of the true filtration markers 51Cr-EDTA (CEDTA) and inulin (CIn), after oral ingestion of cimetidine in 10 healthy men and 29 patients with varying degrees of renal dysfunction. After administration of cimetidine for three to six days, serum creatinine level rose in all participants, while CEDTA and CIn remained stable in a subgroup of 14 subjects in whom they were measured before as well as after the administration of cimetidine. The mean (+/- SD) ratios of CCr to CEDTA (N = 39) and of CCr to CIn (N = 19) after ingestion of cimetidine were 1.02 +/- 0.13 and 1.01 +/- 0.13, respectively, and did not differ significantly from unity. This high degree of accuracy of the cimetidine-aided CCr was present over the entire range of renal function in the study population. Our results also indicated an improved precision of the cimetidine-aided measurement of CCr, resulting in a variability that did not differ significantly from that of the measurement of CEDTA or CIn. We conclude that after oral administration of cimetidine, the creatinine clearance can be used as a reliable measure of GFR within a broad range of renal function.

Definition, incidence, and clinical description of flare in systemic lupus erythematosus. A prospective cohort study

The course of systemic lupus erythematosus (SLE) is characterized by exacerbations (or flares) and remissions of disease activity. As part of an ongoing prospective cohort study, 3 disease activity indices, the physician's global assessment, the Lupus Activity Index, and the University of Toronto SLE Disease Activity Index, have been recorded, at least quarterly since 1987, on 185 SLE patients. We developed a definition of SLE flare and a description of its clinical epidemiology. Disease flare was defined as a change of greater than or equal to 1.0 in the physician's global assessment of disease activity (measured on a 0-3 scale) from the previous visit or from a visit within the last 93 days. Of the 185 patients, 98 (53%) had greater than or equal to 1 flare; the total number of flares was 146. The incidence of flare was 0.65 per patient-year of followup. The median time from the first study visit to a flare was 12 months. Flares were frequently characterized by constitutional symptoms, musculoskeletal involvement, cutaneous involvement, and decreasing levels of C3 and C4. At the time of flare, the mean University of Toronto SLE Disease Activity Index score increased by 3.0 and the mean Lupus Activity Index score (modified to omit the physician's global assessment) increased by 0.26. Overall, 44.8% of the flares prompted a change in treatment. Patients who experienced flares fulfilled more of the SLE criteria at entry and had been followed up for a longer duration after entry into the study, compared with those who did not have flares.(ABSTRACT TRUNCATED AT 250 WORDS)

High-dose intravenous IgG treatment and renal function

In an open trial of high dose intravenous IgG (IVIG) treatment in nephrotic patients with glomerulonephritis, the first six patients so far studied showed a transient rise in plasma creatinine. This increase was not associated with any symptoms and the urinary deposit remained unchanged. Two other patients with pre-existing renal impairment but without nephrotic syndrome had a transient and reversible rise in plasma creatinine immediately after IVIG. These observations suggest that high-dose IVIG infusion can produce short-lived disturbances in renal function in patients with kidney diseases.

Evaluation of kidney function in renal transplant patients receiving long-term cyclosporine

We prospectively assessed renal function in a group of 29 renal transplant patients receiving cyclosporine (CsA) in order to determine the course of their renal function over time and the relationship between different markers of glomerular function. We measured serum creatinine, DPTA, and creatinine clearances, and urinary albumin excretion. The clinical course of 24 patients (83%) permitted repeat studies over a period of 32 +/- 1 (SEM) months, and in these patients DTPA clearance, creatinine clearance, and the serum creatinine concentration did not vary with time. Five of the patients (17%) lost their grafts and returned to dialysis. On initial evaluation patients who lost their grafts had a lower DPTA clearance than those whose function was maintained (29 +/- 3 v 46 +/- 2 mL/min/1.73 m2 body surface area [BSA], respectively, P less than 0.005) and all of them had a DTPA clearance of less than 40 mL/min/1.73 m2 BSA. There was an inverse correlation between the log of the urinary albumin excretion and the DTPA clearance (n = 33, r = -0.59, P less than 0.001), a direct correlation with the serum creatinine concentration (N = 33, r = 0.89, P less than 0.0001), but no correlation with time after transplantation. Thus, despite the continued use of CsA, renal function over time was stable in patients who underwent repeated studies, as was the relationship between the DTPA clearance and the clinically used markers of transplant function, the serum creatinine concentration, and the creatinine clearance.

Accuracy of creatinine clearance in measuring glomerular filtration rate in patients with systemic lupus erythematosus without clinical evidence of renal disease

We sought to determine whether creatinine clearance (Ccr) gives an accurate measurement of the glomerular filtration rate in patients with systemic lupus erythematosus (SLE) with no clinical evidence of renal disease. Eighteen such SLE patients underwent measurement of Ccr and 99mtechnetium-DTPA clearance (CDTPA). The mean +/- SD Ccr:CDTPA ratio was 1.12 +/- 0.15 (95% confidence interval 1.04-1.20). These results indicate that Ccr gives an accurate measurement of the glomerular filtration rate in the majority of SLE patients who do not have clinical evidence of renal disease.