Adaptation of an enzymatic polyfructosan assay to clinical practice

Average creatinine-urea clearance: revival of an old analytical technique?

Background

Creatinine-based equations such as the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) are recommended for estimating glomerular filtration rate (eGFR) in clinical practice, but have reduced performance in advanced stages of chronic kidney disease. However, only rarely studies have evaluated the performance of eGFR by measuring the average of the urinary clearances of creatinine and urea (mCl_UN-cr) compared with the eGFR equations.

Methods

This cross-sectional study evaluated the usefulness of mCl_UN-cr in a population of 855 participants who performed a GFR measurement by urinary inulin clearance. The performance of mCl_UN-cr was compared with those of CKD-EPI 2009 and CKD-EPI 2021, considering three criteria: bias, precision and accuracy.

Results

In the whole sample, the mCl_UN-cr performed similarly to CKD-EPI equations (2009 and 2021) [precision: 11.5 (95% CI 10.5; 12.5) vs 19.0 (95% CI 17.2; 20.1) and 19.1 (95% CI 17.4; 20.4), and accuracy P₃₀: 97.0 (95% CI 95.8; 98.0) vs 82.0 (95% CI 79.2; 84.4) and 77.2 (95% CI 74.5; 80.0)]. The CKD-EPI equations (2009 and 2021) had the best performance when mGFR was >60 mL/min/1.73 m². In contrast, the mCl_UN-cr performed better than others with lowest mGFR values, more noticeable when mGFR was <60 mL/min/1.73 m².

Conclusions

The study described the best performance of mCl_UN-cr at GFR levels below 60 mL/min/1.73 m² and a satisfactory result in the overall cohort. The findings point to a role of this tool, especially for estimating GFR in chronic kidney disease patients in developing countries, when reference measurement of GFR is not available.

Point of care creatinine derived eGFR measurement in capillary blood for identifying patients at risk

Introduction

The aim of the study was to assess the clinical reliability of eGFR values estimated with a creatinine measurement from a point of care (StatSensor®) compared with measured GFR (mGFR) by a gold standard method.

Methods

We prospectively included 113 patients undergoing renal function assessment. We compared eGFR using creatinine from capillary blood or venous blood measured by StatSensor® and measured GFR (mGFR) by Passing Bablok regression. Performance of eGFR was estimated by biais, precision and accuracy.

Results

A total of 113 subjects were included. Median eGFR values were 59 (10–132), 52 (10–123) and 51 (10–131) ml/min/1.73 m² for enzymatic, capillary and venous measurements, respectively. There was no difference between P30 and P10 for the three eGFR values (p = 0.11 and p = 0.1 respectively). StatSensor® eGFR tended to be underestimated compared to mGFR. For CKD stage 4/5 patients, concordance was 79 and 84% for eGFR with capillary creatinine and venous creatinine respectively. For mGFR< 60 ml/min/1.73 m², concordance was 84 and 88% with capillary creatinine and venous creatinine respectively.

Conclusion

The use of a handheld blood creatinine monitoring system with eGFR calculation provides a good estimation of GFR and allow to identify patients at high risk of acute kidney injury.

TmP/GFR reference values from childhood to adulthood in the era of IDMS-standardized creatinine values

BACKGROUND

The assessment of phosphate homeostasis in clinical practice relies on circulating phosphate levels but also on phosphate tubular reabsorption, ideally assessed using the Tubular maximum Phosphate Reabsorption per Glomerular Filtration Rate (TmP/GFR). TmP/GFR reference values were established before the onset of IDMS-standardized creatinine assays, and thus need to be updated. Our objective is to provide reference values for TmP/GFR from childhood to adulthood, using the gold-standard of GFR assessment and IDMS-standardized creatinine values.

METHODS

We retrospectively analyzed all the inulin and iohexol clearances (mGFR) performed in children and in adults screened for a living-donation in our unit since the beginning of IDMS-creatinine assays. TmP/GFR was calculated on a fasting sample, using the conventional formula without correction for TRP in subjects below 19 years of age.

RESULTS

A total of 2051 subjects (1711 children, 340 adults), aged from 1.9 to 73.4 years with normal GFR, normal phosphate and normal calcium levels, was included for TmP/GFR analysis. As expected, there was a progressive decrease along puberty in both genders of plasma phosphate and TmP/GFR, the decrease occurring earlier in girls. After the age of 19, there was a stabilization of plasma phosphate and TmP/GFR levels until the age of 55, phosphate levels and TmP/GFR being slightly lower in men than in women.

CONCLUSION

We present the largest cohort describing TmP/GFR reference values in the era of IDMS-standardized creatinine assays. We believe that these data will help physicians to better diagnose and manage patients with abnormal phosphate metabolism in daily clinical routine.

Evolution of renal function in patients with severe intestinal failure on home parenteral nutrition

BACKGROUND

Kidney disease is a frequent but underestimated complication in patients suffering from intestinal failure (IF) treated by long-term home parenteral nutrition (HPN). The evolution in glomerular filtration rate (GFR) over time is poorly characterized. The current equations for estimating GFR have limited precision. No study has specifically investigated the reliability of recent creatinine-based estimated GFR (eGFR) equations in this population. The aim of this study was to evaluate the renal function decline under home parenteral nutrition (HPN) with a gold standard method and compare the performances of routinely used eGFR equations.

METHODS

Forty patients with HPN and two or more GFR measurements were retrospectively studied. The renal function decline was calculated by the slope drawn between the successive measured GFRs (mGFRs). The performances of the Modification of Diet in Renal Disease, Chronic Kidney Disease Epidemiology Collaboration, full age spectrum and revised Lund-Malmö equations were compared with reference methods (inulin or iohexol clearance).

RESULTS

The mean mGFR was 78 ± 28 mL/min/1.73 m2. The annual decline of mGFR was -1.9 mL/min/1.73 m2/year. No predisposing factor was identified to predict impairment in renal function. eGFR formulas grossly overestimated mGFR and had a low level of accuracy.

CONCLUSIONS

Patients with IF are at significant risk for impaired renal function. In this population, the tested eGFR equations were inaccurate. However, monitoring kidney function with mGFR remains important in these patients, as their GFR regularly declines and no specific risk factor has yet been identified.

Comparison of iohexol plasma clearance formulas vs. inulin urinary clearance for measuring glomerular filtration rate

OBJECTIVES

The one-compartment iohexol plasma clearance has been proposed as a reliable alternative to renal inulin clearance. However, this method's performance depends on the formula used to calculate glomerular filtration rate (GFR). This study reports on performance comparisons between various mathematical formulas proposed for iohexol plasma clearance vs. inulin urinary clearance.

METHODS

GFR was simultaneously determined by inulin and iohexol clearance in 144 participants (age: 10-84 years; glomerular filtration rate: 15-169 mL/min/1.73 m²). A retrospective cross-sectional study evaluated the performance of four formulas proposed to calculate plasma iohexol clearance (Brøchner-Mortensen, Fleming et al., Jødal-Brøchner-Mortensen, and Ng-Schwartz-Munoz). The performance of each formula was assessed using bias, precision (standard deviation of the bias), accuracy (percentage iohexol within 5, 10, and 15%), root mean square error, and concordance correlation coefficient vs. renal inulin clearance as reference.

RESULTS

Regarding accuracy, there was no difference in root mean square error (RMSE), P₅, P₁₀, or P₁₅ between the four formulas. The four concordance correlation coefficients (CCC) between the value from each formula and in-GFR were high and not significantly different. At in-GFR ≥90 mL/min/1.73 m², Ng-Schwartz-Munoz formula performed slightly better than other formulas regarding median bias (-0.5; 95% CI [-3.0 to 2.0] and accuracy P₁₅ (95.0; 95% CI [88.0-100.0]).

CONCLUSIONS

The studied formulas were found equivalent in terms of precision and accuracy, but the Ng-Schwartz-Munoz formula improved the accuracy at higher levels of in-GFR.

Comparison of creatinine-based equations for estimating glomerular filtration rate in deceased donor renal transplant recipients

BACKGROUND

Estimating glomerular filtration rate (GFR) is important for clinical management in kidney transplantation recipients (KTR). However, very few studies have evaluated the performance of the new GFR estimating equations (Lund-Malmö Revised-LMR, and Full Age Spectrum-FAS) in KTR.

METHODS

GFR was estimated (eGFR) using CKD-EPI, MDRD, LMR, and FAS equations and compared to GFR measurement (mGFR) by reference methods (inuline urinary and iohexol plasma clearance) in 395 deceased-donor KTR without corticosteroids. The equations performance was assessed using bias (mean difference of eGFR and mGFR), precision (standard deviation of the difference), accuracy (concordance correlation coefficient-CCC), and agreements (total deviation index-TDI). The area under receiver operating characteristic curves (ROC) and the likelihood ratio for a positive result were calculated.

RESULTS

In the total population, the performance of the CKD-EPI, MDRD and FAS equations was significantly lower than the LMR equation regarding the mean [95%CI] difference in bias (-2.0 [-4.0; -1.5] versus 9.0 [7.5; 10.0], 5.0 [3.5; 6.0] and 10.0 [8.5; 11.0] mL/min/1.73m2, P<0.005) and TDI (17.10 [16.41; 17.88], 25.91 [24.66; 27.16], 21.23 [19.48; 23.13] and 25.84 [24.16; 27.57], respectively). Concerning the CCC, all equation had poor agreement (<0.800) without statically difference between them. However, all equations had excellent area under the ROC curve (>0.900), and LMR equation had the best ability to correctly predict KTR with mGFR<45 mL/min/1.73 m2 (positive likelihood ratio: 8.87 [5.79; 13.52]).

CONCLUSION

Among a referral group of subjects KTR, LMR equation had the best mean bias and TDI, but with no significant superiority in other agreement tools. Caveat is required in the use and interpretation of PCr-based equations in this specific population.

Age-dependent reference intervals for estimated and measured glomerular filtration rate

Background

Defining mean and reference intervals for glomerular filtration rate (GFR) has been the subject of only a limited number of studies and review articles, with contradicting statements about the mean. Normal measured GFR (mGFR) values of ∼120–130 mL/min/1.73 m² have long been the referenced values for young adults but seem to be too high according to recent studies. Reference intervals are difficult to define because of the age decline of GFR, which is also observed in healthy subjects. Little data are available for subjects >70 years of age.

Methods

Based on the reference intervals for serum creatinine (SCr) and the recently published full-age spectrum (FAS) equation, we define simple age-dependent equations for the reference limits of GFR. The mGFR of 633 living potential kidney donors was used to validate the new formulae that define the reference interval.

Results

The reference limits for estimated GFR (eGFR), calculated by entering the reference limits for SCr into the FAS equation closely correspond with published reference limits for mGFR. Of the mGFRs of potential living kidney donors, 97.2% lie between the newly defined reference limits for GFR.

Conclusion

SCr reference limits may serve to define age-dependent reference limits for eGFR and mGFR.

An estimated glomerular filtration rate equation for the full age spectrum

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Can the height-independent Pottel eGFR equation be used as a screening tool for chronic kidney disease in children?

Determination of plasma creatinine (Pcr) should be associated to an estimation of glomerular filtration rate (eGFR). Pottel et al. established a height-independent equation, eGFR = 107.3/(Pcr/Q) where Q is the median of Pcr (Pottel-Belgium). The aims were to 1) determine a local height-independent equation (Pottel-Lyon), 2) evaluate the performance of these equations compared to the Schwartz 2009 and Schwartz-Lyon equations, and 3) evaluate the height-independent equations in laboratory routine. Therefore, 1) all first pediatric Pcr determination (December 2009-June 2011) were collected, and median of Pcr was determined for each 1-year age interval (Q-Lyon), 2) GFR was measured (mGFR) in 359 children (438 measures) and compared to eGFR, and 3) all first Pcr determination (January 2012-June 2013) were used to calculate eGFR with the Pottel-Lyon and the Pottel-Belgium equations. Pcr was determined by an IDMS-standardized enzymatic assay. In the population with a mGFR, the Pottel-Lyon and the Schwartz-Lyon showed the best performance (bias, P10 and P30). However, the performance in identifying patients with a mGFR < 75 mL/min/1.73 m(2) was similar for all the studied equations.

CONCLUSION

The performance of the height-independent and dependent equations to identify mild renal dysfunction is similar. The height-independent Pottel equation could be proposed as an excellent screening tool for kidney disease when height information is not available. "

WHAT IS KNOWN

" • Determination of plasma creatinine in children is rarely associated to an estimation of glomerular filtration rate due to the lack of height information. • Pottel et al. developed a height-independent equation (eGFR = 107.3/(Pcr/Q) where Q is the median of Pcr for each age class. "

WHAT IS NEW

" • The performance of the height-independent (Pottel) or height-dependent (Schwartz) equations is similar to identify renal dysfunction (GFR < 75 mL/min/1.73 m (2) ) in children. • The height-independent Pottel equation could be an excellent screening tool for kidney disease in a general pediatric laboratory when height information is not available.

Effects of chymostatin, a chymase inhibitor, on blood pressure, plasma and tissue angiotensin II, renal haemodynamics and renal excretion in two models of hypertension in the rat

NEW FINDINGS

What is the central question of this study? We examined, in hypertensive rats, whether the angiotensin-converting enzyme-independent enzymes generating angiotensin II in the tissues modulate blood pressure, peripheral circulation and renal function. What is the main finding and its importance? The results suggest that chymostatin-sensitive enzymes diminish vascular tone in renal and extrarenal vascular beds. Chymase or similar chymostatin-sensitive enzymes have a significant role in the synthesis of angiotensin II in different tissues but do not control blood pressure in the short term, similarly in salt-dependent or Goldblatt-type rat hypertension. In salt-dependent hypertension, chymase blockade protected renal outer medullary perfusion, probably by reducing the angiotensin II content in the kidney. Chymase is presumed to be a crucial enzyme of the non-angiotensin-converting enzyme pathway of angiotensin II (Ang II) generation in tissues, a process involved in vascular remodelling and development of hypertension. We examined the role of chymase in hypertension induced by exposure of uninephrectomized rats to high dietary salt intake (UNX HS) and in the Goldblatt renal artery stenosis (two-kidney, one-clip) model. In acute experiments with anaesthetized rats of either model, chymostatin at 2 mg kg(-1) h(-1) or 0.05% DMSO solvent was infused i.v. Mean arterial blood pressure, heart rate, iliac blood flow (a measure of hindlimb perfusion), total renal blood flow and intrarenal regional perfusion (laser-Doppler technique) were measured continuously, along with the glomerular filtration rate and renal excretion. In both models, chymase blockade distinctly decreased plasma and tissue Ang II without lowering mean blood pressure or consistently altering the other functional parameters measured. Unexpectedly, in Goldblatt hypertensive rats the blockade increased the renal and hindlimb vascular resistances by 51 and 33%, respectively (P < 0.05). In UNX HS hypertensive rats, chymase blockade abolished the solvent-induced decrease in outer medullary blood flow. We conclude that chymase or similar chymostatin-sensitive enzyme(s) has a significant role in the synthesis of Ang II in different tissues but does not participate in short-term control of blood pressure in salt-dependent or Goldblatt-type rat hypertension. In the Goldblatt model, chymase appeared to reduce the renal and hindlimb vascular resistances by an unknown mechanism. In salt-dependent hypertension, chymase blockade protected renal outer medullary perfusion, probably by reducing Ang II content in the kidney.

In chronic kidney disease, serum α-Klotho is related to serum bicarbonate and proteinuria

OBJECTIVES

Klotho is an "aging-suppressor" gene and encodes a single-pass transmembrane protein predominantly expressed in renal tubules. Whether chronic kidney disease (CKD) affects serum Klotho is poorly documented. We aimed to measure the relationship of serum α-Klotho with renal function, acid-base status, bone biomarkers, and proteinuria in CKD patients.

DESIGN SETTING, PARTICIPANTS, AND MEASUREMENTS

We measured serum α-Klotho, serum FGF23, and glomerular filtration rate by inulin clearance in 60 CKD patients between January and July 2011. We also measured serum creatinine, bicarbonate, calcium, phosphorus, parathyroid hormone, C-reactive protein, and 25-OH vitamin D. Proteinuria was obtained from a 24-h urine collection.

RESULTS

The median serum α-Klotho was 478 (348-658) pg/mL. We found an inverse relationship between serum α-Klotho and serum creatinine (r = -0.36, P = .007), proteinuria (r = -0.36, P = .013), and a positive relationship with serum bicarbonate (r = 0.33, P = .011). There was no further significant relation between serum α-Klotho and inulin clearance or serum FGF23. Multiple regression analysis including serum bicarbonate, serum creatinine, and proteinuria indicated that only serum bicarbonate was associated with serum α-Klotho (P = .003).

CONCLUSIONS

This study shows that in CKD, serum α-Klotho is related to serum bicarbonate and proteinuria and not to renal function. Further research is required to determine whether correcting these 2 amenable conditions would improve serum α-Klotho.

The relationship between renal function and plasma concentration of the cachectic factor zinc-alpha2-glycoprotein (ZAG) in adult patients with chronic kidney disease

Zinc-α2-glycoprotein (ZAG), a potent cachectic factor, is increased in patients undergoing maintenance dialysis. However, there is no data for patients before initiation of renal replacement therapy. The purpose of the present study was to assess the relationship between plasma ZAG concentration and renal function in patients with a large range of glomerular filtration rate (GFR). Plasma ZAG concentration and its relationship to GFR were investigated in 71 patients with a chronic kidney disease (CKD) stage 1 to 5, 17 chronic hemodialysis (HD), 8 peritoneal dialysis (PD) and 18 non-CKD patients. Plasma ZAG concentration was 2.3-fold higher in CKD stage 5 patients and 3-fold higher in HD and PD patients compared to non-CKD controls (P<0.01). The hemodialysis session further increased plasma ZAG concentration (+39%, P<0.01). An inverse relationship was found between ZAG levels and plasma protein (r_s = −0.284; P<0.01), albumin (r_s = −0.282, P<0.05), hemoglobin (r_s = −0.267, P<0.05) and HDL-cholesterol (r_s = −0.264, P<0.05) and a positive correlation were seen with plasma urea (r_s = 0.283; P<0.01). In multiple regression analyses, plasma urea and HDL-cholesterol were the only variables associated with plasma ZAG (r² = 0.406, P<0.001). In CKD-5 patients, plasma accumulation of ZAG was not correlated with protein energy wasting. Further prospective studies are however needed to better elucidate the potential role of ZAG in end-stage renal disease.

Creatinine- versus cystatine C-based equations in assessing the renal function of candidates for liver transplantation with cirrhosis

Renal dysfunction is frequent in liver cirrhosis and is a strong prognostic predictor of orthotopic liver transplantation (OLT) outcome. Therefore, an accurate evaluation of the glomerular filtration rate (GFR) is crucial in pre-OLT patients. However, in these patients plasma creatinine (Pcr) is inaccurate and the place of serum cystatine C (CystC) is still debated. New GFR-predicting equations, based on standardized assays of Pcr and/or CystC, have been recently recommended in the general population but their performance in cirrhosis patients has been rarely studied. We evaluated the performance of the recently published Chronic Kidney Disease Epidemiology Collaboration equations (CKD-EPI-Pcr, CKD-EPI-CystC, and CKD-EPI-Pcr-CystC) and the more classical ones (4- and 6-variable MDRD and Hoek formulas) in cirrhosis patients referred for renal evaluation before OLT. Inulin clearance was performed in 202 consecutive patients together with the determination of Pcr and CystC with assays traceable to primary reference materials. The performance of the GFR-predicting equations was evaluated according to ascites severity (no, moderate, or refractory) and to hepatic and renal dysfunctions (MELD score  ≤ or >15 and KDOQI stages, respectively). In the whole population, CystC-based equations showed a better performance than Pcr-based ones (lower bias and higher 10% and 30% accuracies). CKD-EPI-CystC equation showed the best performance whatever the ascites severity and in presence of a significant renal dysfunction (GFR <60 mL/min/1.73 m(2)).

CONCLUSION

Pcr-based GFR predicting equations are not reliable in pre-OLT patients even when an IDMS-traceable enzymatic Pcr assay is used. Whenever a CystC-assay traceable to primary reference materials is performed and when a true measurement of GFR is not possible, CystC-based equations, especially CKD-EPI-CystC, may be recommended to evaluate renal function and for KDOQI staging.

Accuracy of GFR estimation in obese patients

BACKGROUND AND OBJECTIVES

Adequate estimation of renal function in obese patients is essential for the classification of patients in CKD category as well as the dose adjustment of drugs. However, the body size descriptor for GFR indexation is still debatable, and formulas are not validated in patients with extreme variations of weight.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This study included 209 stages 1-5 CKD obese patients referred to the Department of Renal Function Study at the University Hospital in Lyon between 2010 and 2013 because of suspected renal dysfunction. GFR was estimated with the Chronic Kidney Disease and Epidemiology equation (CKD-EPI) and measured with a gold standard method (inulin or iohexol) not indexed (mGFR) or indexed to body surface area determined by the Dubois and Dubois formula with either real (mGFRr) or ideal (mGFRi) body weight. Mean bias (eGFR-mGFR), precision, and accuracy of mGFR were compared with the results obtained for nonobese participants (body mass index between 18.5 and 24.9) who had a GFR measurement during the same period of time.

RESULTS

Mean mGFRr (51.6 ± 24.2 ml/min per 1.73 m(2)) was significantly lower than mGFR, mGFRi, and eGFRCKD-EPI. eGFRCKD-EPI had less bias with mGFR (0.29; -1.7 to 2.3) and mGFRi (-1.62; -3.1 to 0.45) compared with mGFRr (8.7; 7 to 10). This result was confirmed with better accuracy for the whole cohort (78% for mGFR, 84% for mGFRi, and 72% for mGFRr) and participants with CKD stages 3-5. Moreover, the Bland Altman plot showed better agreement between mGFR and eGFRCKD-EPI. The bias between eGFRCKD-EPI and mGFRr was greater in obese than nonobese participants (8.7 versus 0.58, P<0.001).

CONCLUSIONS

This study shows that, in obese CKD patients, the performance of eGFRCKD-EPI is good for GFR ≤ 60 ml/min per 1.73 m(2). Indexation of mGFR with body surface area using ideal body weight gives less bias than mGFR scaled with body surface area using real body weight.

A new equation to estimate the glomerular filtration rate in children, adolescents and young adults

BACKGROUND

A new estimated glomerular filtration rate (eGFR) equation, designed for isotope dilution mass spectrometry-standardized serum creatinine (Scr), is presented for use in children, adolescent boys and girls and young adults.

METHODS

The new equation, eGFR = 107.3/(Scr/Q), is based on the concept of normalized Scr: Q is the normalization value and is considered as the Scr concentration for the average healthy child, adolescent or young adult of a specific height (L) and is modeled as a height-dependent polynomial of the fourth degree.

RESULTS

The well-known Schwartz equation [eGFR = kL/Scr, k = 0.413 (Schwartz) or k = 0.373 (Schwartz-Lyon)] for children between 1 and 14 years can be seen as a special case of the new equation for which the Q-polynomial is simplified to a linear equation: Q = 0.0035 × L (cm). The new eGFR equation has been validated in a data set of n = 750 children, adolescents and young adults aged 10-25, against the true GFR (inulin method), and outperforms the selected (but most used) creatinine-based eGFR equations for children, mainly in the healthy GFR region.

CONCLUSIONS

The new Q(height)-eGFR equation serves as an excellent screening tool for kidney disease in 1-25-year-old children, adolescents and young adults.

The relation between renal function and serum sclerostin in adult patients with CKD

BACKGROUND AND OBJECTIVES

Sclerostin, a bone antianabolic peptide involved in osteoporosis, is elevated in patients undergoing maintenance dialysis. However, there are no data for patients with early CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Between January and July 2010, serum sclerostin and GFR (calculated by inulin clearance) were measured in 90 patients with CKD. Fasting blood samples were also drawn for determination of calcium, phosphorus, parathyroid hormone, bone alkaline phosphatase, and 25-OH vitamin D.

RESULTS

Median GFR was 66.5 (interquartile range, 40.0-88.3) ml/min per 1.73 m(2). Median sclerostin level was 53.5 (interquartile range, 37.5-77.2) pmol/L, was higher in patients with a GFR <60 ml/min per 1.73 m(2), and was highest in those with ESRD. Sclerostin levels were significantly more elevated in men than women (P<0.05). An inverse relationship was found between sclerostin and GFR (r=-0.58; P<0.001), and a positive correlation was seen with age (r=0.34; P<0.01) and serum phosphate (r=0.26; P=0.02). In multiple regression analyses, GFR, sex, and serum phosphate were the only variables associated with serum sclerostin (P<0.001). Age lost its relationship with sclerostin level.

CONCLUSIONS

This is the first study reporting higher serum sclerostin levels starting at CKD stage III. GFR, sex, and serum phosphate were the only measures associated with sclerostin level, suggesting that the effect of age reported in the literature might instead be attributable to the altered renal function in the elderly. Correcting the serum phosphorus level may be associated with lower sclerostin levels.

Deferasirox-induced renal impairment in children: an increasing concern for pediatricians

BACKGROUND

Deferasirox (DFX) is an oral iron chelator with an established dose-dependent efficacy in transfusion-related iron overload. Whereas emerging long-term data confirm the safety of the drug, with transient moderate elevation of serum creatinine level, several authors have reported renal tubular dysfunction. The aim of this study was to evaluate tubular and glomerular function before and after the initiation of DFX therapy in a pediatric patient population.

METHODS

Ten children (4 girls, mean age 12.4 ± 3.9 years) enrolled in a routine blood transfusion program were treated with 24.8 ± 9.6 mg/kg per day of DFX, and renal function was assessed before and 17.2 ± 8.9 months after the initiation of DFX therapy.

RESULTS

Prior to treatment with DFX, all patients had a normal glomerular function rate (GFR) (125 ± 15 ml/min per 1.73 m(2)) and normal tubular function. Following the initiation of DFX therapy, the GFR decreased by approximately 20 % with one patient with a GFR of <80 mL/min per 1.73 m(2) and seven patients with a GFR of <100 mL/min per 1.73 m(2). Two patients experienced a generalized proximal tubular dysfunction whereas nine patients presented at least one sign of proximal tubular dysfunction.

CONCLUSIONS

Renal toxicity is a frequent adverse event of DFX treatment, presenting as both glomerular and proximal dysfunction. A routine renal assessment is therefore required to prevent chronic kidney disease that may result from prolonged tubular injury.

GFR estimation in adolescents and young adults

The performance of creatinine-based equations to obtain the estimated GFR in adolescents and young adults is poorly understood. We assessed creatinine-based GFR estimating equations in a cross-section of 751 adolescents and young adults (1054 measurements), using inulin clearance (measured GFR [mGFR]) as the reference method. We evaluated the following: Cockcroft-Gault, four-variable Modified Diet in Renal Disease, and the Chronic Kidney Disease Epidemiology Collaboration equations for adult participants, as well as the Schwartz 2009 and Schwartz-Lyon equations for pediatric age groups. Participants ranged in age from 10 to 26 years (mean 16.8 years); we divided the population into four groups according to age (10-12 years, 13-17 years, 18-21 years, and 21-25 years). Evaluation of the agreement between these formulas and mGFR (e.g., correlation, Bland-Altman plots, bias, and accuracy) showed that there was a good correlation between mGFR and both pediatric formulas in all age groups, whereas the adult formulas substantially overestimated mGFR. In conclusion, we recommend the use of pediatric equations to estimate GFR from childhood to early adulthood.

Estimating glomerular filtration rate in kidney transplant recipients: performance over time of four creatinine-based formulas

BACKGROUND

The management of kidney transplant recipients requires accurate estimate of glomerular filtration rate (GFR). This study aims at evaluating the performance of four creatinine-based formulas for estimating the GFR (estimated GFR) in this population.

METHODS

Performances of Cockcroft and Gault formula, Modification of Diet in Renal Disease (MDRD) simplified formula, Chronic Kidney Disease Epidemiology Collaboration formula, and Nankivell formula were assessed compared with inulin clearance taken as the gold standard for measuring GFR (measured GFR). Performances were assessed using the first measurements of GFR obtained in 1249 subjects. How estimated GFR tracks changes in measured GFR over time since transplantation in those patients with repeated measures was also assessed.

RESULTS

The MDRD formula provided the best estimate of GFR with a mean bias of -0.5 mL/min/1.73 m, a standard deviation of bias of 12 mL/min/1.73 m, and a 30% accuracy at 85%. The MDRD formula also seemed to provide the best performance for estimating GFR, irrespective of age, stage of renal failure, and in people whose body mass index was more than 18.5 kg/m. This robustness is important in clinical practice. The performance of the four formulas was not modified by the posttransplant period.

CONCLUSION

Even if 30% accuracy was suboptimal in the Kidney Disease Outcomes Quality Initiative guidelines, our results, obtained in a large number of patients, lead us to recommend using the MDRD formula to monitor GFR in kidney transplant recipients.

Which creatinine and cystatin C equations can be reliably used in children?

BACKGROUND AND OBJECTIVES

Estimation of GFR in children is challenging; reference methods are cumbersome, and formulas have limitations. The aims of this study were to evaluate (1) the new creatinine-based formula recently proposed by Schwartz using a kinetic colorimetric compensated Jaffe technique; (2) some cystatin C-derived formulas (Hoek, Le Bricon, Larsson, Rule, Filler, and Zappitelli) using a nephelemetric technique; and (3) combined formulas using both cystatin and creatinine (Zappitelli and Bouvet).

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

These formulas were evaluated in a cross-sectional cohort of 252 children with moderate CKD or normal GFR, in comparison with the reference standard (inulin clearance, iGFR). Mean age, body weight, height, creatinine, and cystatin C were 10.7 ± 4.0 years, 35 ± 15 kg, 137 ± 20 cm, 55 ± 30 μmol/L, and 0.91 ± 0.35 mg/L, respectively.

RESULTS

Mean ± SD iGFR was 101 ± 32 ml/min per 1.73 m². When evaluating agreement between these formulas and iGFR (e.g. correlation, Bland Altman plots, bias, and accuracies), there was a good correlation between iGFR and all Le Bricon, Larsson, Rule, and Zappitelli (both) and locally adapted Schwartz and 2009 Schwartz formulas; by contrast, Filler and original 1976 Schwartz formulas overestimated iGFR, whereas Hoek and Bouvet formulas underestimated iGFR.

CONCLUSION

Different cystatin C-derived formulas (at least Larsson and Le Bricon) for estimating GFR as well as the Zappitelli combined formula are accurate in addition to the new Schwartz bedside formula in a general pediatric population.