Simple sampling strategy for measuring inulin renal clearance

Serum and plasma levels of Ba, but not those of soluble C5b-9, might be affected by renal function in chronic kidney disease patients

BACKGROUND

During the last few decades, pathogenic mechanisms associated with uncontrolled activation of the complement (C) system and development of anti-C agents have been closely investigated in the field of nephrology. The usefulness of some C products such as C5a and sC5b-9 for diagnostic and prognostic purposes remains controversial. On the other hand, decreased renal function is being observed in many patients with or without nephritis as a background factor in progressively aging societies. We therefore investigated whether renal function influenced the evaluation of various complement components and activation products.

METHODS

To investigate the influence of renal function on evaluations of C3, C4, CH50, Ba, C5a and sC5b-9, 40 patients were retrospectively chosen from among 844 patients without active glomerulonephritis from 2009 to 2016. We measured plasma and serum levels of C3, C4, CH50, Ba, C5a and sC5b-9 using enzyme-linked immunosorbent assays and compared the findings with inulin clearance (Cin) as a marker of preserved renal function.

RESULTS

Both plasma and serum levels of Ba correlated significantly with Cin, but other values did not. Compared with patients with Cin ≥ 60 or ≥ 30 mL/min/1.73 m², plasma and serum levels of Ba were increased in patients with Cin decreased to < 60 or < 30 mL/min/1.73 m², but levels of C5a and sC5b-9 were not.

CONCLUSION

The influence of renal function might need to be considered when evaluating Ba, but not C5a and sC5b-9, in plasma and serum samples from chronic kidney disease patients.

d-Serine Mediates Cellular Proliferation for Kidney Remodeling

Background

d-serine, a long-term undetected enantiomer of serine, is a biomarker that reflects kidney function and disease activity. The physiologic functions of d-serine are unclear.

Methods

The dynamics of d-serine were assessed by measuring d-serine in human samples of living kidney donors using two-dimensional high-performance liquid chromatography, and by autoradiographic studies in mice. The effects of d-serine on the kidney were examined by gene expression profiling and metabolic studies using unilateral nephrectomy mice, and genetically modified cells.

Results

Unilateral nephrectomy in human living kidney donors decreases urinary excretion and thus increases the blood level of d-serine. d-serine is quickly and dominantly distributed to the kidney on injection in mice, suggesting the kidney is a main target organ. Treatment of d-serine at a low dose promotes the enlargement of remnant kidney in mouse model. Mechanistically, d-serine activates the cell cycle for tissue remodeling through an mTOR-related pathway.

Conclusions

d-serine is a physiologic molecule that promotes kidney remodeling. Besides its function as a biomarker, d-serine has a physiologic activity that influences kidney function.

Adequacy of decision-making based on each kidney function estimation method for Japanese living kidney donor candidates: a retrospective observational study

Background

Living kidney transplantation comprises the majority of kidney transplantations in Japan. Living kidney donors should be assured of their own health. Therefore, Japanese guidelines define the criterion of kidney function for living donors. Glomerular filtration rates (GFR) ≥ 70 mL/min/1.73 m2 are required for marginal donors. The guidelines require that GFRs of donors be measured by the inulin (In) clearance method (CIn) or the radioisotope method, but these methods can be substituted with the creatinine (Cr) clearance method (CCr). Methods for estimating kidney function are susceptible to error, and decision-making regarding donor eligibility could be affected by the estimation method used. We investigated the adequacy of decision-making based on kidney function estimation methods used in Japanese living kidney donor candidates by comparing CCr or estimated GFR (eGFR), calculated by several equations, and CIn as measured GFR (mGFR).

Methods

In total, 210 people, including 36 actual kidney donor candidates, who had both CIn and CCr measured at Shinshu University Hospital from April 2011 to April 2015, were included. Cr and cystatin C (Cys) levels measured at the same time were used to calculate eGFR (eGFRCr and sGFRCys, respectively). We evaluated the concordance rates of cases whose GFR levels were ≥ 70 mL/min/1.73 m2 in this study and assumed that they were living kidney donor candidates. Only kidney donor candidates underwent an additional sensitivity analysis.

Results

Median CIn and CCr were 55.5 mL/min/1.73 m2 and 68.0 mL/min/1.73 m2, respectively. CCr had the highest tendency to overestimate kidney function. Some participants were incorrectly evaluated as adequate using CCr, despite their mGFR being inadequate for living kidney donors according to the guidelines. These results were independent of sex or actual living kidney donor candidates. The average of eGFRCr and eGFRCys was well correlated with CIn.

Conclusions

Kidney function estimated by CCr is not equal to the mGFR. When using CCr as a kidney function estimation method to determine the adequacy of a living kidney donor, it should be noted that CCr overestimates kidney function. In evaluating adequacy for a marginal donor, GFR estimated by CIn should be assessed.

Influence of muscle mass on the estimation of glomerular filtration rate in Japanese terminal cancer patients

BACKGROUND

Estimated glomerular filtration rate (eGFR) based on serum cystatin C (Scys) is useful for patients with decreased muscle mass, but has been also reported to be affected by cancer. The usefulness of Scys in eGFR in terminal cancer patients with decreased muscle mass is unknown. Therefore, we analyzed appropriate eGFR formulae for terminal cancer patients.

METHODS

Study design was a retrospective observational study. Based on creatinine height index (CHI), 184 terminal cancer patients were stratified into CHI ≥ 90% (normal muscle mass, 59 patients); CHI 60-89% (mildly to moderately decreased muscle mass, 64 patients); and CHI < 60% (severely decreased muscle mass, 61 patients) groups. Twenty-four-hour creatinine clearance was measured and converted to the glomerular filtration rate (GFR) as a renal function measure. To estimate GFR, various eGFR formulae for Japanese were used: eGFR_Scys, eGFR_Scr5 and eGFR_Scr3, eGFR_average and eGFR_Scys-Scr, and eGFR_CG, based on Scys, serum creatinine (Scr), Scys and Scr combined, and Cockcroft-Gault formula (CG), respectively. Errors between measured and estimated values of renal function were verified using mean prediction errors (ME). When a 95% confidence interval (CI) of ME included 0, the accuracy of the eGFR formula was graded as good.

RESULTS

eGFR_Scys ME was 0.2 (95% CI lower limit - 3.7, upper limit 4.0) mL/min/1.73 m² in CHI 60-89% group and 9.2 (6.1, 12.9) mL/min/1.73 m² in CHI < 60% group. eGFR_Scys was most accurate among the eGFR formulae.

CONCLUSIONS

eGFR based on Scys was demonstrated as useful in terminal cancer patients with decreased muscle mass.

Increased Glomerular Hydrostatic Pressure is Associated with Tubular Creatinine Reabsorption in Healthy Subjects

<b><i>Background:</i></b> Cr is secreted by the proximal tubules and thus Cr clearance (<i>C</i>_cr) can overestimate inulin clearance (<i>C</i>_in). However, in some cases, <i>C</i>_cr can even underestimate <i>C</i>_in. This suggests that Cr could be reabsorbed in the tubuli. We examined the clinical parameters that are associated with tubular Cr reabsorption. <b><i>Methods:</i></b> In 80 kidney donor candidates (53.9 ± 13.2 years, 29 males), <i>C</i>_in and para-aminohippuric acid clearance were measured simultaneously. Intrarenal hemodynamic parameters were calculated by Gomez’s formulae. To quantify the secretory component of <i>C</i>_cr (SF_cr), it was calculated as follows: SF_cr = (<i>C</i>_cr − <i>C</i>_in)/<i>C</i>_cr. <b><i>Results:</i></b> Twenty-five subjects (31.3%) showed SF_cr values &#x3c;0. SF_cr that correlated significantly and negatively with efferent arteriolar resistance (<i>R</i>_e) and glomerular hydrostatic pressure (<i>P</i>_glo) (<i>R</i>_e: <i>r</i> = −0.30, <i>p</i> = 0.008; <i>P</i>_glo: <i>r</i> = −0.28, <i>p</i> = 0.025). In multiple regression analyses, <i>R</i>_e and <i>P</i>_glo were significantly and negatively associated with SF_cr after adjustment for other confounders. <b><i>Conclusions:</i></b> These findings suggest that tubular reabsorption of Cr can occur in some cases. Intrarenal glomerular hemodynamic burden may be related to tubular creatinine reabsorption, which possibly leads to lower <i>C</i>_cr values.

D-Serine reflects kidney function and diseases

_D-Amino acids, long-term undetected enantiomers of _L-amino acids, are now emerging as potential biomarkers, especially for kidney diseases. Management of chronic kidney disease (CKD), a global problem with its high prevalence and poor prognosis, is currently unsatisfactory due to the difficulty in estimating kidney function and in early detection of diseases. We now show that intra-body dynamics of _D-serine reflect kidney function and diseases. The blood level of _D-serine correlated well with the actual glomerular filtration ratio, a key kidney function. This correlation was compatible with those of conventional kidney markers, and blood level of _D-serine was relatively unaffected by such clinical factors as body size. The balance between excretion and reabsorption of amino acids by the kidney was controlled with chiral selectivity, and the reabsorption of _D-serine was sensitive to the presence of CKD. The combination of blood level and urinary dynamics of _D-serine effectively distinguished CKD from non-CKD. These lines of evidence provide new insights into the enantioselective amino acid dynamics in the human body that reflect disease pathophysiology. _D-Serine may serve as a vital biomarker that suppress CKD onset through the precise assessment of kidney function and the diagnosis of CKD.

Association of Albuminuria With Intraglomerular Hydrostatic Pressure and Insulin Resistance in Subjects With Impaired Fasting Glucose and/or Impaired Glucose Tolerance

OBJECTIVE

Little is known about the relationships between insulin resistance, intrarenal hemodynamics, and urinary albumin excretion (UAE) in humans with impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT). The aim of the current study was to examine intrarenal hemodynamic abnormalities, insulin resistance, and UAE in subjects with IFG or IGT. We hypothesized that intrarenal hemodynamic abnormalities would be associated with insulin resistance.

RESEARCH DESIGN AND METHODS

Fifty-four kidney donors underwent 75-g oral glucose tolerance and inulin and para-aminohippuric acid clearance testing. Insulin sensitivity index (ISI) was evaluated by the Matsuda index. Intrarenal hemodynamic parameters were calculated by the Gomez formulae.

RESULTS

Of the 54 subjects, 33 exhibited IFG or IGT and 31 exhibited normal glucose tolerance (NGT). Glomerular hydrostatic pressure (P_glo) and UAE were significantly higher in the IFG or IGT subjects with obesity (P = 0.015 and 0.0001, respectively). Log ISI correlated significantly and negatively with P_glo (r = -0.351, P = 0.009) in all subjects. In multiple regression analyses among all subjects, log ISI was associated significantly and independently with P_glo (β = -0.316, P = 0.015), after adjustment for age, sex, and systolic blood pressure. Further, BMI (β = 0.517, P = 0.0004), P_glo (β = 0.420, P = 0.004), and log ISI (β = -0.366, P = 0.008) were each associated significantly and independently with UAE after adjustment.

CONCLUSIONS

We demonstrated that increased insulin resistance is associated with increased P_glo and UAE in IFG or IGT subjects. These hemodynamic burdens and insulin resistance may cause injury to the glomeruli even in subjects with IFG or IGT.

Optimal equation for estimation of glomerular filtration rate in autosomal dominant polycystic kidney disease: influence of tolvaptan

BACKGROUND

The reliability of various equations for estimating the GFR in ADPKD patients and the influence of tolvaptan on the resulting estimates have not been examined when GFR is calculated on the basis of inulin clearance.

METHODS

We obtained baseline and on-tolvaptan measured GFRs (mGFRs), calculated on the basis of inulin clearance, in 114 ADPKD, and these mGFRs were compared with eGFRs calculated according to four basic equations: the MDRD, CKD-EPI, and JSN-CKDI equations and the Cockcroft-Gault formula, as well as the influence of tolvaptan and of inclusion of cystatin C on accuracy of the results. Accuracy of each of the seven total equations was evaluated on the basis of the percentage of eGFR values within mGFR ± 30% (P₃₀).

RESULTS

mGFRs were distributed throughout CKD stages 1-5. Regardless of the CKD stage, P₃₀s of the MDRD, CKD-EPI, and JSN-CKDI equations did not differ significantly between baseline values and on-tolvaptan values. In CKD 1-2 patients, P₃₀ of the CKD-EPI equation was 100.0%, whether or not the patient was on-tolvaptan. In CKD 3-5 patients, P₃₀s of the MDRD, CKD-EPI, and JSN-CKDI equations were similar. For all four equations, regression coefficients and intercepts did not differ significantly between baseline and on-tolvaptan values, but accuracy of the Cockcroft-Gault formula was inferior to that of the other three equations. Incorporation of serum cystatin C reduced accuracy.

CONCLUSIONS

The CKD-EPI equation is most reliable, regardless of the severity of CKD. Tolvaptain intake has minimal influence and cystatin C incorporation does not improve accuracy.

Clinical benefits of using inulin clearance and cystatin C for determining glomerular filtration rate in HIV-1-infected individuals treated with dolutegravir

INTRODUCTION

Dolutegravir may inhibit creatinine transporters in renal tubules and elevate serum creatinine levels. We investigated the usefulness of glomerular filtration rate (GFR) measured using inulin clearance (Cin), creatinine clearance (Ccr), and estimated GFR based on both serum creatinine (eGFRcre) and serum cystatin C (eGFRcys).

PATIENTS & METHODS

HIV-1-infected Japanese patients with suppressed viremia and whose antiretroviral drug was switched to dolutegravir from other drugs were included (n = 108, Study 1). We compared eGFRcre and eGFRcys at the start and after 48 weeks of dolutegravir administration. For the patients providing consent, we measured Cin and Ccr (n = 15, Study 2). We assessed biases and accuracy and compared Cin with eGFRcre, eGFRcys, and Ccr.

RESULTS

There were no differences in serum cystatin C and eGFRcys between baseline and at 48 weeks. Moreover, eGFRcre was significantly less accurate (within 30% of measured GFR) than both eGFRcys and Ccr (40% accuracy compared to 93% and 93%, respectively). eGFRcys was significantly less biased than eGFRcre and Ccr (p < 0.0001, p = 0.00036, respectively). No significant difference between Cin and eGFRcys was observed. eGFRcys was significantly correlated with Cin (γ = 0.85, p < 0.0001).

CONCLUSIONS

eGFRcys provided the most precise estimate and most closely approximate Cin in HIV-1-infected Japanese patients with suppressed viremia treated with dolutegravir. We demonstrated clinical benefits of inulin clearance and eGFRcys. This is the first study performing inulin clearance for HIV-1-infected individuals and to show data for eGFRcys from a large cohort following a switch to dolutegravir from other antiretroviral agents.

Retrospective Comparison of Estimated GFR using 2006 MDRD, 2009 CKD-EPI and Cockcroft-Gault with 24 Hour Urine Creatinine Clearance

INTRODUCTION

The assessment of Glomerular Filtration Rate (GFR) is essential for clinical practice in assessing kidney function, drug dosing, detecting and estimating the prognosis of Chronic Kidney Disease (CKD). The most common practical method for assessing GFR is performed with a 24 hour/timed urine collection for creatinine clearance evaluation. The estimation of eGFR by creatinine based formulae is known to be a rapid and reliable means of approximation of creatinine clearance.

AIM

To compare eGFR using three commonly used Formulae {Modification of Diet in Renal Disease Study Equation (MDRD 2006), Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI 2009) and Cockcroft-Gault Formula} with 24 hour creatinine clearance and to identify which amongst the 3 formulae for eGFR closely correlates with 24 hour creatinine clearance in a secondary care hospital.

MATERIALS AND METHODS

We retrospectively collected laboratory data requested for 24 hour creatinine clearance in the period from January 2014 to August 2016. Totally 91 laboratory request for 24 hour creatinine clearance data were obtained. The paired-t-test was used for comparison since all parameters used in the study were numerical, all patients came from same population and all had paired results.

RESULTS

The eGFR by MDRD formulae had a statistically insignificant p-value (p > 0.05) i.e., good approximation in the II^nd, III^rd, IV^th and V^th stages of CKD on comparison with 24 hour creatinine clearance. The eGFR by CKD-EPI formulae had a statistically insignificant p-value (p > 0.05) in the II^nd, IV^th and V^th stages of CKD. The eGFR by Cockcroft-Gault Formulae had a statistically insignificant p-value (p > 0.05) in the I^st, II^nd and V^th stages of CKD.

CONCLUSION

The Creatinine based GFR estimation provides a more accurate assessment of 24 hour creatinine clearance and kidney function than measuring serum creatinine alone but have certain limitations in few clinical circumstances. No single equation will be optimal for all populations. But the result of this study showed MDRD 2006 formulae to be more accurate than CKD-EPI 2009 and Cockcroft-Gault formulae in estimating GFR, detection of CKD, drug dosing and estimating prognosis.

U-shaped relationship between serum uric acid levels and intrarenal hemodynamic parameters in healthy subjects

Hyperuricemia has been reported to affect renal hemodynamics. In a recent study, both low and high levels of serum uric acid (SUA) were found to be associated with loss of kidney function. The goal of this study was to evaluate the relationship between SUA levels and intrarenal hemodynamic parameters in healthy subjects, using plasma clearance of para-aminohippurate (C_PAH) and inulin (C_in). Renal and glomerular hemodynamics were evaluated by simultaneous measurements of C_PAH and C_in in 48 healthy subjects (54.6 ± 13.4 yr). Intrarenal hemodynamic parameters, including efferent and afferent (R_a) arteriolar resistance, were calculated using Gómez's formulas. Relationships of SUA levels with these intrarenal hemodynamic parameters were examined. In quadratic regression analysis, SUA levels had a significant inverse U-shaped relationship with C_in (P < 0.0001, R² = 0.350) and C_PAH (P = 0.0093, R² = 0.188) and a U-shaped relationship with R_a (P = 0.0011, R² = 0.262). In multiple regression analysis with normal (3.5-6.0 mg/dl) and mildly low or high (<3.5 or >6.0 mg/dl) SUA levels entered as dummy variables of zero and one, respectively, mildly low or high SUA levels were significantly and independently associated with R_a (β = 0.230, P = 0.0403) after adjustment for several factors (R² = 0.597, P < 0.0001). Both mild hyperuricemia and mild hypouricemia are significantly associated with increased R_a, although weakly. The increase in R_a in subjects with mild hyperuricemia or hypouricemia may be related to renal hemodynamic abnormalities, possibly leading to a decline in renal function.

Utility of Cystatin C for Estimating Glomerular Filtration Rate in Patients With Muscular Dystrophy

Emerging concerns regarding heart failure, arrhythmia, and sudden death in patients with muscular dystrophy are of significant clinical importance. On the other hand, little attention has been paid to renal dysfunction because these patients have low serum creatinine levels. Serum cystatin C, unaffected by muscle quantity, is a potentially superior marker for estimating renal function. Here, we present cases with muscular dystrophy in which estimated glomerular filtration rate (GFR) by cystatin C (eGFRcys) provided good agreement with simultaneously measured GFR by inulin renal clearance (differences less than 20%). Sudden death with acute heart failure occurred in a patient with underlying renal dysfunction and elevated BNP. Neurologists and cardiologists should evaluate renal function using GFR with cystatin C in patients with muscular dystrophy.

Development of a rat model of D-galactosamine/lipopolysaccharide induced hepatorenal syndrome

AIM: To develop a practical and reproducible rat model of hepatorenal syndrome for further study of the pathophysiology of human hepatorenal syndrome.

METHODS: Sprague-Dawley rats were intravenously injected with D-galactosamine and lipopolysaccharide (LPS) via the tail vein to induce fulminant hepatic failure to develop a model of hepatorenal syndrome. Liver and kidney function tests and plasma cytokine levels were measured after D-galactosamine/LPS administration, and hepatic and renal pathology was studied. Glomerular filtration rate was detected in conscious rats using micro-osmotic pump technology with fluorescein isothiocyanate-labelled inulin as a surrogate marker.

RESULTS: Serum levels of biochemical indicators including liver and kidney function indexes and cytokines all significantly changed, especially at 12 h after D-galactosamine/LPS administration [alanine aminotransferase, 3389.5 ± 499.5 IU/L; blood urea nitrogen, 13.9 ± 1.3 mmol/L; Cr, 78.1 ± 2.9 μmol/L; K⁺, 6.1 ± 0.5 mmol/L; Na⁺, 130.9 ± 1.9 mmol/L; Cl^-, 90.2 ± 1.9 mmol/L; tumor necrosis factor-α, 1699.6 ± 599.1 pg/mL; endothelin-1, 95.9 ± 25.9 pg/mL; P < 0.05 compared with normal saline control group]. Hepatocyte necrosis was aggravated gradually, which was most significant at 12 h after treatment with D-galactosamine/LPS, and was characterized by massive hepatocyte necrosis, while the structures of glomeruli, proximal and distal tubules were normal. Glomerular filtration rate was significantly decreased to 30%-35% of the control group at 12 h after D-galactosamine/LPS administration [Glomerular filtration rate (GFR)₁, 0.79 ± 0.11 mL/min; GFR₂, 3.58 ± 0.49 mL/min·kgBW^-1; GFR₃, 0.39 ± 0.99 mL/min·gKW^-1]. The decreasing timing of GFR was consistent with that of the presence of hepatocyte necrosis and liver and kidney dysfunction.

CONCLUSION: The joint use of D-galactosamine and LPS can induce liver and kidney dysfunction and decline of glomerular filtration rate in rats which is a successful rat model of hepatorenal syndrome.

Clinical impact of kidney function on presepsin levels

OBJECTIVE

Presepsin is highlighted as a diagnostic and prognostic marker of sepsis. Little information is available regarding the accurate association between presepsin levels and the degree of kidney function. We analyzed presepsin levels in patients with a glomerular filtration rate (GFR) in the categories G1 to G5, evaluated via inulin renal clearance test, and receiving hemodialysis (HD).

METHODS

Patients who were not receiving HD were included if they had undergone inulin renal clearance measurements for the accurate measurement of GFR (measured GFR), and patients who were receiving hemodialysis (HD) were included if they had anuria. Exclusion criteria were infection, cancer, liver disease, autoimmune disorders, or steroid or immunosuppressant use. GFR category was defined as follows; G1: GFR ≥ 90 ml/min/1.73 m2, G2: GFR = 60 to 90 ml/min/1.73 m2, G3: GFR = 30 to 60 ml/min/1.73 m2, G4: GFR = 15 to 30 ml/min/1.73 m2, G5: GFR ≤ 15 ml/min/1.73 m2.

RESULTS

Seventy-one patients were included. The median (IQR) presepsin values of patients in each GFR category were as follows: G1 + G2: 69.8 (60.8-85.9) pg/ml; G3: 107.0 (68.7-150.0) pg/ml; G4: 171.0 (117.0-200.0) pg/ml; G5: 251.0 (213.0-297.5) pg/ml; and HD: 1160.0 (1070.0-1400.0) pg/ml. The log-transformed presepsin values, excluding patients receiving HD, inversely correlated with the measured GFR (Pearson's correlation coefficient = -0.687, P < 0.001). The multivariate analysis revealed that measured GFR and hemoglobin levels significantly correlated with elevated presepsin levels.

CONCLUSION

Presepsin levels were markedly high in patients receiving HD, similar to values seen in patients with severe sepsis or septic shock. In patients who were not receiving HD, presepsin levels increased as GFR decreased. Thus, the evaluation of presepsin levels in patients with chronic kidney disease requires further consideration, and a different cutoff value is needed for diagnosing sepsis in such patients.

Renal function evaluation in patients with cancer who were scheduled to receive carboplatin or S-1

BACKGROUND

Accurate glomerular filtration rate (GFR) evaluation is significant for drug dosing of carboplatin, anticancer drug excreted mainly from kidney. Serum cystatin-C (sCys-C) is a GFR marker with little affected by body muscle mass volume. And GFR equations based on serum creatinine (eGFRcreat) and sCys-C (eGFRcys) were developed; however, accuracy of eGFRcys has not been elucidated fully among patients with cancer. Therefore, we analyzed the performance of GFR equations among patients with cancer whose GFR values were measured by inulin clearance (Cin).

METHODS

Study design was a cross-sectional study. Subjects were 41 patients with cancer whose GFR values were measured by Cin for drug dosing studies of carboplatin or S-1 in Nagoya University Hospital from 2007 to 2010 and 29 non-cancer patients. Correlation with Cin and slope of regression line were evaluated in eGFRcreat and eGFRcys. Single and multiple regression analyses were analyzed to identify associating factors with eGFRcreat/Cin or eGFRcys/Cin.

RESULTS

Age, body weight, body mass index (BMI) and sCr were different between cancer patients and non-cancer patients, but sCys-C and Cin were consistent in 2 groups. The slope of the regression line for Cin vs. eGFRcys with zero intercept in cancer patients was 1.10 (95 % CI: 1.02-1.17), which was significantly different from 1.0. In multiple regression analysis revealed that BMI and urinary creatinine excretion were significantly associated with eGFRcreat/Cin, and cancer was only associating factor with eGFRcys/Cin.

CONCLUSION

eGFRcys should not be used for evaluation of renal function in patients with cancer because it underestimates GFR.

Significant association between glycemic status and increased estimated postglomerular resistance in nondiabetic subjects - study of inulin and para-aminohippuric acid clearance in humans

We investigated whether glomerular hemodynamic parameters in nondiabetic subjects, including healthy subjects, are associated with glycemic status indices, by simultaneous measurement of inulin (C_in) and para-aminohippuric acid (C_PHA) clearance. Twenty-six subjects (age 49.5 ± 13.3 years; 13 men and 13 women; 14 healthy subjects and 12 subjects with mild proteinuria) were enrolled. C_in and C_PAH were measured simultaneously. All 26 subjects were nondiabetics. Estimated preglomerular resistance, estimated postglomerular resistance, and estimated glomerular hydrostatic pressure (P_glo) were calculated according to Gomez’ formula. P_glo correlated significantly and positively with hemoglobin A1c (HbA1c) in both healthy subjects (r = 0.532, P = 0.0498) and subjects with mild proteinuria (r = 0.681, P = 0.015). While there was no significant correlation between estimated preglomerular resistance and HbA1c, estimated postglomerular resistance correlated significantly and positively with HbA1c both in healthy subjects (r = 0.643, P = 0.013) and subjects with mild proteinuria (r = 0.589, P = 0.044). Glomerular filtration fraction, estimated P_glo and estimated postglomerular resistance in total subjects were associated significantly with HbA1c after adjustment for age, gender, and body mass index. These results demonstrate that, even in nondiabetic subjects, glycemic status is associated with estimated postglomerular resistance, but not estimated preglomerular resistance. It is suggested that increased estimated postglomerular resistance associated with higher HbA1c levels, even within the normal range, causes increased estimated P_glo, leading to increased FF. Thus, hemodynamic abnormalities associated with higher HbA1c levels may be related to glomerular hypertension, even in nondiabetic subjects.

Modification of diet in renal disease (MDRD) study and CKD epidemiology collaboration (CKD-EPI) equations for Taiwanese adults

Background

Estimated glomerular filtration rate (eGFR) using the Modification of Diet in Renal Disease (MDRD) study or the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations may not be accurate for Asians; thus, we developed modified eGFR equations for Taiwanese adults.

Methods

This cross-sectional study compared the Taiwanese eGFR equations, the MDRD study, and the CKD-EPI equations with inulin clearance (C_in). A total of 695 adults including 259 healthy volunteers and 436 CKD patients were recruited. Participants from the Kaohsiung Medical University Hospital were used as the development set (N = 556) to develop the Taiwanese eGFR equations, whereas participants from the National Taiwan University Hospital were used as the validation set (N = 139) for external validation.

Results

The Taiwanese eGFR equations were developed by using the extended Bland-Altman plot in the development set. The Taiwanese MDRD equation was 1.309×MDRD^0.912, Taiwanese CKD-EPI was 1.262×CKD-EPI^0.914 and Taiwanese four-level CKD-EPI was 1.205×four-level CKD-EPI^0.914. In the validation set, the Taiwanese equations had the lowest bias, the Taiwanese equations and the Japanese CKD-EPI equation had the lowest RMSE, whereas the Taiwanese and the Japanese equations had the best precision and the highest P₃₀ among all equations. However, the Taiwanese MDRD equation had higher concordance correlation than did the Taiwanese CKD-EPI, the Taiwanese four-level CKD-EPI and the Japanese equations. Moreover, only the Taiwanese equations had no proportional bias among all of the equations. Finally, the Taiwanese MDRD equation had the best diagnostic performance in terms of ordinal logistic regression among all of the equations.

Conclusion

The Taiwanese MDRD equation is better than the MDRD, CKD-EPI, Japanese, Asian, Thai, Taiwanese CKD-EPI, and Taiwanese four-level CKD-EPI equations for Taiwanese adults.

Significant association of poor glycemic control with increased resistance in efferent arterioles--study of inulin and para-aminohippuric acid clearance in humans

AIMS

To examine whether glomerular hemodynamic parameters in humans are associated with glycemic control indices, by simultaneously measuring clearance of inulin (Cin) and para-aminohippuric acid (CPHA).

METHODS

Thirty-one subjects (age 55.4±14.7 years; 15 men and 16 women; 21 diabetics and 10 non-diabetics) were enrolled. Cin and CPAH were measured simultaneously. Afferent arteriolar resistance (Ra), efferent arteriolar resistance (Re), glomerular hydrostatic pressure (Pglo) and glomerular filtration fraction (FF) were calculated according to Gomez' formula.

RESULTS

FF correlated significantly and positively with fasting plasma glucose (FPG), hemoglobin A1c (HbA1c) and glycated albumin (GA) (r=0.396, p=0.0303; r=0.587, p=0.0007; r=0.525, p=0.0070, respectively). Pglo correlated significantly and positively with FPG, HbA1c and GA (r=0.572, p=0.0008; r=0.535, p=0.0019; r=0.540, p=0.0053, respectively). Although there was no significant correlation between Ra and glycemic control indices, Re correlated significantly and positively with HbA1c and GA (r=0.499, p=0.0043; r=0.592, p=0.0018, respectively). FF, Pglo and Re were associated significantly with HbA1c and GA after adjustment for age.

CONCLUSIONS

These results demonstrate, in humans, that poor glycemic control is associated with increased Re, but not Ra. It is suggested that increased Re causes increased Pglo, leading to increased FF. Thus, hemodynamic abnormalities with poor glycemic control may be related to glomerular hypertension in humans.

Poor glycemic control is a major factor in the overestimation of glomerular filtration rate in diabetic patients

OBJECTIVE Serum creatinine levels are lower in diabetic patients compared with their nondiabetic counterparts. Therefore, estimated glomerular filtration rate (eGFR) is higher in the former than in the latter group. Factors associated with overestimation of renal function in diabetic patients were examined, and new formulae reflecting precise eGFR were created. RESEARCH DESIGN AND METHODS Eighty subjects (age 56.5 ± 15.4 years; 35 males [43.8%]; 40 patients with diabetes and 40 nondiabetic subjects) were enrolled. GFR was evaluated by inulin clearance (Cin). eGFR values were calculated based on serum creatinine and/or serum cystatin C levels. The factors related to the dissociation between eGFR and Cin in diabetic patients and the agreement among each of three eGFR and Cin were compared. RESULTS Although Cin was not significantly different between the diabetic and nondiabetic subjects (P = 0.2866), each of three eGFR measures from the diabetic patients was significantly higher than that of the nondiabetic subjects (P < 0.01). There were significant and positive correlations between the ratio of each eGFR/Cin, hemoglobin A1c, and glycated albumin. The intraclass correlation coefficients in diabetic patients were weaker than those in the nondiabetic subjects, and the intercepts of the regression lines between each eGFR measure and Cin in the diabetic patients were significantly higher than those of the nondiabetic subjects. New formulae for the calculation of eGFR corrected by the glycemic control indices were better than the original eGFR, particularly in diabetic patients. CONCLUSIONS eGFR overestimates Cin as glycemic controls worsen. eGFR corrected by hemoglobin A1c is considered to be clinically useful and feasible.

Utility of cystatin C for renal function in amyotrophic lateral sclerosis

OBJECTIVES

Creatinine (Cr) as a marker of renal function has limited value in amyotrophic lateral sclerosis (ALS) because patients with ALS have reduced muscle mass. Thus, there is a need for alternative methods of assessing renal function. Cystatin C (CysC), which is unaffected by muscle mass, is potentially an ideal biomarker of nephrotoxicity in ALS; however, its utility requires validation.

MATERIAL AND METHODS

One hundred and six subjects were recruited for the study: 76 ALS patients and 30 healthy controls. We compared the Cr-based estimated glomerular filtration rate (eGFR) with the CysC-based eGFR in the ALS patients and healthy controls. The results were further analysed according to the severity of ALS in the patients.

RESULTS

The mean Cr-based eGFRs were 257.2 ± 383.1 ml/min/1.73 m(2) in the ALS group and 98.1 ± 34.9 in the control group; however, the mean CysC-based eGFRs were not significantly different between both groups. Thus, the Cr-based eGFR in the ALS group was markedly higher than any of the other values. Although serum CysC levels did not correlate with the severity of ALS according to the ALS Functional Rating Scale-Revised, strong simple correlations were observed between serum Cr levels and the severity of ALS (correlation coefficient = 0.734, P < 0.001).

CONCLUSIONS

This study demonstrates the potential usefulness of CysC as a biomarker of renal function in ALS patients. Furthermore, its applicability could be extended to other neuromuscular diseases.

Measurement of glomerular filtration rate by rapid intravenous injection of a newly developed inulin fraction

OBJECTIVE

Since the conventional drip-infusion method for measuring inulin clearance (Cin) has problems related to its accuracy and performance, we explored a more accurate and concise method by rapid intravenous injection of a newly developed inulin fraction (Inulead(®)), in which spot urine sampling was omitted and the administration period of inulin was shortened from 120 to 5 minutes.

PATIENTS AND METHODS

Twenty seven patients (M/F: 15/12, 67.8 ± 12.9 years old) admitted to the Nephrology ward were enrolled in this study. Inulead(®), 1500 mg dissolved in 150 mL of saline, was intravenously administered in 5 minutes. Then, sequential blood samplings and urine collection were performed for 24 hours. Cins were calculated by the following three formulae: (1) a pharmacokinetic analysis using a two compartments model based on the plasma inulin concentration to determine Cin, which was the administered dose divided by the area under the curve (AUC) from 0 to ∞, (2) urinary inulin excretion divided by the AUC for 24 hours and (3) the Bayesian method using a three-point set of plasma inulin concentrations to predict the change of inulin concentration to determine Cin as in 1. These Cins were compared with levels of estimated GFR (eGFR), creatinine clearance (Ccr), serum β2 microglobulin (β2MG) and serum cystatin C (Cys C).

RESULTS

Cins obtained by the above three methods were well correlated with each other (r. = 0.9088 (- )0.9998) and with eGFR (r. = 0.8286 - 0.8650), Ccr (r. = 0.821 - 0.864), 1/β2MG (r. = 0.631 - 0.752) and 1/CysC (r. = 0.830 - 0.857). The averaged differences of each Cin from eGFR were distributed between - 4.4 and - 4.5 mL/min.

CONCLUSION

Since the Cins by rapid inulin injection showed satisfactory correlation and differences with other GFR parameters, this method will be a good alternative to the drip infusion method, and may reduce the burden of patients and medical staff.

Comparison of a simple and a standard method for inulin renal clearance

BACKGROUND

The standard method of renal inulin clearance consists of three sets of 30-min clearances. We previously proposed a simple method with a single urine collection for 1 h and two blood samples. In this study, we compared the two methods.

METHODS

The study involved 112 individuals. Three sets of 30-min urine sample collections were started 45 min after inulin infusion , and serum concentrations were measured at the midpoint (60, 90, 120 min) of each clearance period. The mean of the three (Cin-ST) or average of the first two (Cin-ST2) clearances was used for the standard method. Clearance calculated by the simple method (Cin-S) combined the first two collections and the mean of serum concentrations at the beginning (45 min) and end (105 min) of the clearance period. Clearance was also calculated by estimated area under the plasma concentration curve from 45 to 105 min (Cin-A) as a more reliable value.

RESULTS

Cin-S correlated highly with Cin-ST (r = 0.992). Bland-Altman plot indicated that Cin-S was lower than Cin-ST at the same rate in all glomerular filtration rate (GFR) ranges. Total Cin-S of all patients was significantly lower (5.9%, 4.8%, and 3.6%) than Cin-ST, Cin-ST2, and Cin-A, respectively. Cin-ST2 was 1.3% higher than Cin-A. The change in serum inulin concentration by time from 45 to 105 min was not linear but concave. This led to the underestimation of clearance by the simple method.

CONCLUSION

The simple method of renal inulin clearance gives slightly lower results than the standard method. The difference was small, indicating the simple method is accurate enough for use in clinical practice.

Utility of cystatin C to monitor renal function in Duchenne muscular dystrophy

Creatinine as a marker of renal function has limited value in Duchenne muscular dystrophy (DMD) because of reduced muscle mass. Alternative methods of assessing renal function are sorely needed. Cystatin C, a nonglycosylated protein unaffected by muscle mass, is potentially an ideal biomarker of nephrotoxicity for this population but requires validation. In all, 75 subjects were recruited: 35 DMD (mean age 10.8 +/- 5.4 years, corticosteroids n = 19, ambulatory n = 26), 29 healthy controls, 10 with renal disease, and one DMD with renal failure. Cystatin C levels in DMD were normal irrespective of age, ambulation, or corticosteroid treatment. Serum cystatin C was 0.67 +/- 0.11 mg/l compared to normal controls 0.69 +/- 0.09. mg/l. In these same individuals serum creatinine was severely reduced (0.27 +/- 0.12 mg/dl) versus normals (0.75 +/- 0.15 mg/dl, P < 0.01). In one DMD subject in renal failure, cystatin C was elevated. This study demonstrates the potential value of cystatin C as a biomarker for monitoring renal function in DMD. Its applicability extends to other neuromuscular diseases.