How should proteinuria be detected and measured?

Association of the endothelial nitric oxide synthase gene G894T polymorphism with the risk of diabetic nephropathy in Qassim region, Saudi Arabia-A pilot study

BACKGROUND

Diabetic nephropathy (DN) is a chronic microangiopathic complication of type 2 diabetes mellitus (DM).Vascular endothelial dysfunction resulting from impaired nitric oxide synthase (NOS) activity in the vascular endothelial cells has been suggested as playing an important role in the pathogenesis of diabetic nephropathy (DN). Endothelial nitric oxide synthase (E-NOS) gene G894T polymorphism has been reported to be associated with endothelial dysfunction leading to DN. Our objective was to evaluate the association of G894T polymorphism of eNOS gene with the risk of DN among type 2 diabetic Saudi patients.

METHODS

One hundred and twenty subjects were included in this study. They were divided into three groups. Group I, 40 controls. Group II, 40 type 2 diabetic patients without nephropathy. Group III, 40 type2 diabetic patients with nephropathy. Endothelial nitric oxide synthase (eNOS) G894Tpolymorphism was detected by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Plasma nitric oxide (NO) levels were estimated.

RESULTS

E-NOS genotype frequency showed non-significant differences among the all studied groups (p > 0.05). Both diabetic groups had significantly higher plasma nitrate levels than in controls with a significant increase in group III than in group II patients (all p < 0.0001). E NOS 894TT genotype was associated with higher plasma nitrate levels in all groups.

CONCLUSION

E-NOS gene SNP is not considered as genetic risk factor for DN among type 2 diabetic Saudi patients. The higher plasma levels of nitrates as a marker of oxidative stress in diabetic patients with nephropathy suggest the possible role of oxidative stress but not e-NOS gene SNP in pathogenesis of the DN.

Elevated uric acid level as a significant predictor of chronic kidney disease: a cohort study with repeated measurements

BACKGROUND

Cohort studies evaluating increased serum uric acid (SUA) level as a chronic kidney disease (CKD) risk factor have yielded variable results. We aimed to assess the association between the pattern of longitudinal changes in SUA and incident CKD [estimated glomerular filtration rate (eGFR) <60 ml/min/1.73 m(2)].

METHODS

A population-based cohort study was conducted on 3,605 participants who were followed prospectively for a mean of 5.18 years. The longitudinal changes in SUA were categorized into three subgroups: persistently low, fluctuated (reduced or elevated), and persistently high. The primary outcome of interest was the development of CKD at a follow-up examination. Cox proportional hazards analysis was used to test the hypothesis.

RESULTS

After adjustment for potential confounders, participants with fluctuated SUA with progressively elevated level and persistently high SUA level had significantly higher risk of developing CKD compared to subjects with persistently low SUA level: adjusted hazard ratio (95% confidence interval) was 2.05 (1.24-3.38) vs. 1.90 (1.34-2.71). This longitudinal relationship was independent of sex, age, body mass index, and hypertension status.

CONCLUSIONS

Longitudinally elevated SUA independently predicts the risk of new-onset CKD.

Nonalbuminuric proteinuria as a biomarker for tubular damage in early development of nephropathy with type 2 diabetic patients

AIM

The aim of this study was to evaluate the association between urinary nonalbumin protein (NAP) and urinary tubular markers in early diabetic nephropathy.

METHODS

Urinary NAP was measured in 118 patients with type 2 diabetes with estimated glomerular filtration rates (eGFR) ≥60 mL/min/1.73 m². Urine levels of tubular markers [kidney injury molecule (KIM)-1, neutrophil gelatinase-assoicated lipocalin (NGAL) and liver-type fatty acid-binding protein (L-FABP)] were measured by using an Enzyme-linked immunosorbent assay (ELISA). Patients were divided into three groups according to urinary NAP values.

RESULTS

The urine levels of KIM-1, NGAL and L-FABP were significantly higher in the third tertile group than in the first tertile group (all p < 0.001). There was a significant positive correlation between NAP and each tubular marker (KIM-1, NGAL and L-FABP) in univariate analysis (all p < 0.001). Urinary NAP was positively correlated with all urinary tubular markers after adjustment for age, duration of diabetes, systolic blood pressure, eGFR, low-density lipoprotein cholesterol, HbA1c and albumin-to-creatinine ratio (KIM-1 r = 0.170, p < 0.001; NGAL r = 0.142, p < 0.015 and L-FABP r = 0.262, p < 0.001). In normoalbuminuric patients (n = 58), urinary NAP was also significantly correlated with NGAL and L-FABP in multivariate regression analyses (r = 0.302, p = 0.030 and r = 0.430, p = 0.001).

CONCLUSIONS

These findings suggest that urinary NAP reflects tubular damage in the early-stage type 2 diabetic nephropathy (eGFR ≥ 60 mL/min/1.73 m²). We suggest that urinary NAP could be used as a biomarker for tubular damage in clinical practice.

Contrast-associated AKI and use of cardiovascular medications after acute coronary syndrome

BACKGROUND AND OBJECTIVES

AKI after coronary angiography is associated with poor long-term outcomes. The relationship between contrast-associated AKI and subsequent use of prognosis-modifying cardiovascular medications is unknown.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

A cohort study of 5911 participants 66 years of age or older with acute coronary syndrome who received a coronary angiogram in Alberta, Canada was performed between November 1, 2002, and November 30, 2008. AKI was identified according to Kidney Disease Improving Global Outcomes AKI criteria.

RESULTS

In multivariable logistic regression models, compared with participants without AKI, those with stages 1 and 2-3 AKI had lower odds of subsequent use of angiotensin-converting enzyme inhibitors/angiotensin receptor blocker within 120 days of hospital discharge (adjusted odds ratio, 0.65; 95% confidence interval, 0.53 to 0.80 and odds ratio, 0.34; 95% confidence interval, 0.23 to 0.48, respectively). Subsequent statin and β-blockers use within 120 days of hospital discharge was significantly lower among those with stages 2-3 AKI (adjusted odds ratio, 0.44; 95% confidence interval, 0.31 to 0.64 and odds ratio, 0.46; 95% confidence interval, 0.31 to 0.66, respectively). These associations were consistently seen in patients with diabetes mellitus, heart failure, low baseline eGFR, and albuminuria; 952 participants died during subsequent follow-up after hospital discharge (mean=3.1 years). The use of each class of cardiovascular medication was associated with lower mortality, including among those who had experienced AKI.

CONCLUSIONS

Strategies to optimize the use of cardiac medications in people with AKI after coronary angiography might improve care.

Short-term change in eGFR and risk of cardiovascular events

Background

Lower estimated glomerular filtration rate (eGFR) on a single occasion is associated with risk of cardiovascular events; whether the degree of change in eGFR during a 1‐year period adds prognostic information is unknown.

Methods and Results

We included adults who had ≥2 outpatient eGFR measurements (≥6 months apart) during a 1‐year accrual period in Alberta, Canada. According to recent guidelines, we used a change in eGFR category (≥90, 60 to 89, 45 to 59, 30 to 44, 15 to 29, and <15 mL/min per 1.73 m²), and the presence/absence of a ≥25% change from baseline to classify participants into 5 groups: certain drop, uncertain drop, stable (no change), uncertain rise, and certain rise. We calculated adjusted rates of cardiovascular events (per 10 000 person‐years) for each group. We estimated the adjusted risks of cardiovascular events associated with each category of change in eGFR, in reference to stable kidney function. Among the 526 388 participants, 76.1% (n=400 560) had stable, 2.6% (n=13 668) had a certain drop, and 3.3% (n=17 499) had a certain rise in eGFR. Compared with participants with stable kidney function, adjusted risks of myocardial infarction, heart failure, and stroke were 27%, 51%, and 20% higher, respectively, for those with a certain drop in kidney function. After adjusting for the last eGFR at the end of the accrual period, the observed association diminished.

Conclusion

Clinically relevant changes in eGFR are associated with increased risk of cardiovascular events. However, most of the apparent increase in risk can be accounted for by assessing comorbidity and baseline kidney function.

Investigation of apparent non-albuminuric proteinuria in a primary care population

BACKGROUND

There is debate as to whether using the urinary albumin- or protein-to-creatinine ratio (ACR or PCR) should be the primary test for proteinuria. Whilst albuminuria (increased ACR) in the absence of proteinuria (increased PCR) may be expected in some patients, the converse (i.e., proteinuria in the absence of albuminuria) is more unusual and its cause and significance are unclear. We investigated the nature of such apparent non-albuminuric proteinuria in a primary care population of patients.

METHODS

ACR and PCR were measured in 569 urine samples from patients who either had chronic kidney disease or were at increased risk of the condition. Samples with apparent proteinuria (PCR ≥23 mg/mmol/≥200 mg/g) but no albuminuria (ACR <3.4 mg/mmol/<30 mg/g) were classified as 'discrepant' (37% of proteinuric samples, 6% of all samples); 27 of these samples were available for further analyses. The further analyses included electrophoresis, repeat measurement, immunoassays for markers of tubular proteinuria and use of alternative albumin and total protein methods.

RESULTS

Electrophoresis did not identify significant proteinuria in the discrepant samples. The only evidence of tubular proteinuria following measurement of three urinary markers of the condition was a mildly increased α1-microglobulin-to-creatinine ratio in 10 of the 27 discrepant samples analysed, four of which also had a raised β-trace protein-to-creatinine ratio. Use of an alternative urinary total protein method resulted in significantly lower PCRs and 17 of the 27 samples were no longer classified as proteinuric.

CONCLUSIONS

We were unable to confirm the cause of a raised PCR without albuminuria in these patients and suspect that in most cases it is artefactual.

KDOQI US commentary on the 2012 KDIGO clinical practice guideline for the evaluation and management of CKD

The National Kidney Foundation-Kidney Disease Outcomes Quality Initiative (NKF-KDOQI) guideline for evaluation, classification, and stratification of chronic kidney disease (CKD) was published in 2002. The KDOQI guideline was well accepted by the medical and public health communities, but concerns and criticisms arose as new evidence became available since the publication of the original guidelines. KDIGO (Kidney Disease: Improving Global Outcomes) recently published an updated guideline to clarify the definition and classification of CKD and to update recommendations for the evaluation and management of individuals with CKD based on new evidence published since 2002. The primary recommendations were to retain the current definition of CKD based on decreased glomerular filtration rate or markers of kidney damage for 3 months or more and to include the cause of kidney disease and level of albuminuria, as well as level of glomerular filtration rate, for CKD classification. NKF-KDOQI convened a work group to write a commentary on the KDIGO guideline in order to assist US practitioners in interpreting the KDIGO guideline and determining its applicability within their own practices. Overall, the commentary work group agreed with most of the recommendations contained in the KDIGO guidelines, particularly the recommendations regarding the definition and classification of CKD. However, there were some concerns about incorporating the cause of disease into CKD classification, in addition to certain recommendations for evaluation and management.

The total urine protein-to-creatinine ratio can predict the presence of microalbuminuria

Background

The Kidney Disease: Improving Global Outcomes chronic kidney disease (CKD) guidelines recommend that CKD be classified based on the etiology, glomerular filtration rate (GFR) and degree of albuminuria. The present study aimed to establish a method that predicts the presence of microalbuminuria by measuring the total urine protein-to-creatinine ratio (TPCR) in patients with cardiovascular disease (CVD) risk factors.

Methods and Results

We obtained urine samples from 1,033 patients who visited the cardiovascular clinic at St. Luke's International Hospital from February 2012 to August 2012. We measured the TPCR and the urine albumin-to-creatinine ratio (ACR) from random spot urine samples. We performed correlation, receiver operating characteristic (ROC) curve, sensitivity, and subgroup analyses. There was a strong positive correlation between the TPCR and ACR (R² = 0.861, p<0.001). A ROC curve analysis for the TPCR revealed a sensitivity of 94.4%, a specificity of 86.1%, and an area under the curve of 0.903 for detecting microalbuminuria for a TPCR cut-off value of 84 mg/g of creatinine. The subgroup analysis indicated that the cut-off value could be used for patients with CVD risk factors.

Conclusions

These results suggest that the TPCR with an appropriate cut-off value could be used to screen for the presence of microalbuminuria in patients with CVD risk factors. This simple, inexpensive measurement has broader applications, leading to earlier intervention and public benefit.

Association between First Nations ethnicity and progression to kidney failure by presence and severity of albuminuria

BACKGROUND

Despite a low prevalence of chronic kidney disease (estimated glomerular filtration rate [GFR]<60 mL/min per 1.73 m2), First Nations people have high rates of kidney failure requiring chronic dialysis or kidney transplantation. We sought to examine whether the presence and severity of albuminuria contributes to the progression of chronic kidney disease to kidney failure among First Nations people.

METHODS

We identified all adult residents of Alberta (age≥18 yr) for whom an outpatient serum creatinine measurement was available from May 1, 2002, to Mar. 31, 2008. We determined albuminuria using urine dipsticks and categorized results as normal (i.e., no albuminuria), mild, heavy or unmeasured. Our primary outcome was progression to kidney failure (defined as the need for chronic dialysis or kidney transplantation, or a sustained doubling of serum creatinine levels). We calculated rates of progression to kidney failure by First Nations status, by estimated GFR and by albuminuria category. We determined the relative hazard of progression to kidney failure for First Nations compared with non-First Nations participants by level of albuminuria and estimated GFR.

RESULTS

Of the 1 816 824 participants we identified, 48 669 (2.7%) were First Nations. First Nations people were less likely to have normal albuminuria compared with non-First Nations people (38.7% v. 56.4%). Rates of progression to kidney failure were consistently 2- to 3-fold higher among First Nations people than among non-First Nations people, across all levels of albuminuria and estimated GFRs. Compared with non-First Nations people, First Nations people with an estimated GFR of 15.0-29.9 mL/min per 1.73 m2 had the highest risk of progression to kidney failure, with similar hazard ratios for those with normal and heavy albuminuria.

INTERPRETATION

Albuminuria confers a similar risk of progression to kidney failure for First Nations and non-First Nations people.

Comparison of associations of urine protein-creatinine ratio versus albumin-creatinine ratio with complications of CKD: a cross-sectional analysis

BACKGROUND

Urine albumin-creatinine ratio (ACR) and protein-creatinine ratio (PCR) are important markers of kidney damage and are used for prognosis in persons with chronic kidney disease (CKD). Despite how commonly these measurements are done in clinical practice, relatively few studies have directly compared the performance of these 2 measures with regard to associations with clinical outcomes, which may inform clinicians about which measure of urinary protein excretion is best. We studied the association of ACR and PCR with common complications of CKD.

STUDY DESIGN

Cross-sectional study.

SETTING & PARTICIPANTS

3,481 participants with CKD in the Chronic Renal Insufficiency Cohort (CRIC) Study.

PREDICTORS

ACR and PCR.

OUTCOMES

We examined the association between ACR and PCR with measures of common CKD complications: serum hemoglobin, bicarbonate, parathyroid hormone, phosphorus, potassium, and albumin.

MEASUREMENTS

Restricted cubic spline analyses adjusted for estimated glomerular filtration rate (eGFR; calculated by the MDRD [Modification of Diet in Renal Disease] Study equation) were performed to study the continuous association with our predictors with each outcome.

RESULTS

Mean eGFR was 43±13 (SD)mL/min/1.73 m2 and median values for PCR and ACR were 140 and 46 mg/g, respectively. In continuous analyses adjusted for eGFR, higher ACRs and PCRs were similar and both were associated with lower serum hemoglobin, bicarbonate, and albumin levels and higher parathyroid hormone, phosphorus, and potassium levels. Across all outcomes, the associations of ACR and PCR were similar, with only small absolute differences in the outcome measure. Similar associations were seen in patients with diabetes mellitus.

LIMITATIONS

Participants largely had moderate CKD with low values for ACR and PCR, so results may not be generalizable to all CKD populations.

CONCLUSIONS

In persons with CKD, ACR and PCR are relatively similar in their associations with common complications of CKD. Thus, routine measurement of PCR may provide similar information as ACR in managing immediate complications of CKD.

Predictors of end-stage renal disease in the urban poor

We sought to examine the influence of social and clinical factors on risk of progression of chronic kidney disease (CKD) to end-stage renal disease (ESRD) in the urban poor. We studied 15,353 individuals with moderate-to-advanced CKD who received ambulatory care within a large public health system during 1996-2005. The primary outcome was progression to ESRD. Overall, 559 cases of ESRD occurred over a median follow-up of 2.8 years. Among traditional predictors of ESRD, younger age, male sex, non-White race/ethnicity, public health insurance coverage, diabetes, lower kidney function, higher proteinuria, lower hemoglobin level, and lower serum albumin concentration were significantly associated with a higher adjusted ESRD risk (p<.001 for all). There was no significant association between HIV/AIDS (p=.07), viral hepatitis (p=.11), or non-English language (p=.27) and ESRD risk. Our results highlight the importance of addressing traditional risk factors for progressive CKD to reduce the disproportionate burden of ESRD among disadvantaged populations.

Neutrophil gelatinase-associated lipocalin and albuminuria as predictors of acute kidney injury in patients treated with goal-directed haemodynamic therapy after major abdominal surgery

BACKGROUND

Neutrophil gelatinase-associated lipocalin (NGAL) is emerging as a new biomarker for the early identification of acute kidney injury (AKI). There is also increasing evidence of an association between urinary albumin/creatinine ratio (ACR) and AKI. The primary aim of this study was to evaluate the clinical utility of these biomarkers to predict AKI in a population of perioperative patients treated with goal-directed haemodynamic therapy (GDHT). Secondary aims were to examine NGAL and ACR as sensitive biomarkers to detect the effects of GDHT and to investigate the association of these biomarkers with secondary outcomes.

METHODS

Urine was obtained from 109 patients admitted to a critical care unit following major abdominal surgery. Patients were treated with intravenous fluid, GDHT with intravenous fluid or GDHT with intravenous fluid and dopexamine. Urine was collected preoperatively, and at times 0, 8 and 24 h postoperatively and outcome monitored for 28 days.

RESULTS

There were no significant differences in NGAL or ACR concentrations between the cohorts treated with GDHT compared to standard care. However, both biomarker concentrations rose significantly in all cohorts over the time points. There were no significant differences in NGAL observed between patients who developed AKI and those who did not. However, there were significantly higher ACR preoperatively in patients who developed AKI. There were higher NGAL concentrations in patients who developed an infection and who died.

CONCLUSIONS

NGAL has a poor predictive role in evaluating AKI in this clinical setting. Preoperative ACR may have a role as an AKI marker.

Measurement of renal function in patients with chronic kidney disease

Chronic kidney disease affects millions of people worldwide and is associated with an increased morbidity and mortality as a result of kidney failure and cardiovascular disease. Accurate assessment of kidney function is important in the clinical setting as a screening tool and for monitoring disease progression and guiding prognosis. In clinical research, the development of new methods to measure kidney function accurately is important in the search for new therapeutic targets and the discovery of novel biomarkers to aid early identification of kidney injury. This review considers different methods for measuring kidney function and their contribution to the improvement of detection, monitoring and treatment of chronic kidney disease.

Association of chronic kidney disease (CKD) and failure to monitor renal function with adverse outcomes in people with diabetes: a primary care cohort study

Background

Chronic kidney disease (CKD) is a known risk factor for cardiovascular events and all-cause mortality. We investigate the relationship between CKD stage, proteinuria, hypertension and these adverse outcomes in the people with diabetes. We also study the outcomes of people who did not have monitoring of renal function.

Methods

A cohort of people with type 1 and 2 diabetes (N = 35,502) from the Quality Improvement in Chronic Kidney Disease (QICKD) cluster randomised trial was followed up over 2.5 years. A composite of all-cause mortality, cardiovascular events, and end stage renal failure comprised the outcome measure. A multilevel logistic regression model was used to determine correlates with this outcome. Known cardiovascular and renal risk factors were adjusted for.

Results

Proteinuria and reduced estimated glomerular filtration rate (eGFR) were independently associated with adverse outcomes in people with diabetes. People with an eGFR <60 ml/min, proteinuria, and hypertension have the greatest odds ratio (OR) of adverse outcome; 1.58 (95% CI 1.36-1.83). Renal function was not monitored in 4460 (12.6%) people. Unmonitored renal function was associated with adverse events; OR 1.35 (95% CI 1.13-1.63) in people with hypertension and OR 1.32 (95% CI 1.07-1.64) in those without.

Conclusions

Proteinuria, eGFR < 60 ml/min, and failure to monitor renal function are associated with cardiovascular and renal events and mortality in people with diabetes.

Serum phosphate as a risk factor for cardiovascular events in people with and without chronic kidney disease: a large community based cohort study

BACKGROUND

Serum phosphate is a known risk factor for cardiovascular events and mortality in people with chronic kidney disease (CKD), however data on the association of these outcomes with serum phosphate in the general population are scarce. We investigate this relationship in people with and without CKD in a large community-based population.

METHODS

Three groups from an adult cohort of the Quality Improvement in Chronic Kidney Disease (QICKD) cluster randomised trial (ISRCTN56023731) were followed over a period of 2.5 years: people with normal renal function (N = 24,184), people with CKD stages 1-2 (N = 20,356), and people with CKD stages 3-5 (N = 13,292). We used a multilevel logistic regression model to determine the association between serum phosphate, in these groups, and a composite outcome of all-cause mortality, cardiovascular events, and advanced coronary artery disease. We adjusted for known cardiovascular risk factors.

FINDINGS

Higher phosphate levels were found to correlate with increased cardiovascular risk. In people with normal renal function and CKD stages 1-2, Phosphate levels between 1.25 and 1.50 mmol/l were associated with increased cardiovascular events; odds ratio (OR) 1.36 (95% CI 1.06-1.74; p = 0.016) in people with normal renal function and OR 1.40 (95% CI 1.09-1.81; p = 0.010) in people with CKD stages 1-2. Hypophosphatemia (<0.75 mmol/l) was associated with fewer cardiovascular events in people with normal renal function; OR 0.59 (95% CI 0.36-0.97; p = 0.049). In people with CKD stages 3-5, hyperphosphatemia (>1.50 mmol/l) was associated with increased cardiovascular risk; OR 2.34 (95% CI 1.64-3.32; p<0.001). Other phosphate ranges were not found to have a significant impact on cardiovascular events in people with CKD stages 3-5.

CONCLUSIONS

Serum phosphate is associated with cardiovascular events in people with and without CKD. Further research is required to determine the mechanisms underlying these associations.

Proteinuria and rate of change in kidney function in a community-based population

Proteinuria identifies patients at risk for adverse clinical outcomes, but it is unclear whether proteinuria correlates with the rate of renal decline. We examined the association between proteinuria and rate of change in estimated GFR (eGFR) in a cohort of 638,150 adults from a province-wide registry in Alberta, Canada, who had a measure of proteinuria and three or more outpatient serum creatinine measurements over a period of ≥1 year. An adjusted sex-specific linear mixed-effects model was used to determine the rate of change in eGFR per year for patients with normal, mild, and heavy proteinuria, stratified by baseline kidney function (eGFR ≥90, 60-89.9, 45-59.9, 30-44.9, and 15-29.9 ml/min per 1.73 m(2)). In men, heavy proteinuria and a baseline eGFR of 45-59.9 ml/min per 1.73 m(2) correlated with a change in eGFR of -2.16 (95% confidence interval [CI], -2.37 to -1.95) ml/min per 1.73 m(2) per year, whereas mild proteinuria and a baseline eGFR of 30-44.9 ml/min per 1.73 m(2) correlated with a change in eGFR of -0.51 (95% CI, -0.70 to -0.32) ml/min per 1.73 m(2) per year. Similar trends were observed for female, elderly, and diabetic patients. Notably, normal protein levels and a lower baseline eGFR (15-29.9 ml/min per 1.73 m(2)) correlated with stable or improved renal function. In conclusion, our results suggest that proteinuria of increasing severity is associated with a faster rate of renal decline, regardless of baseline eGFR, and the combined effect should be considered in patients with CKD.

Empiricism or rationalism: how should we measure proteinuria?

Proteinuria is the cardinal sign of renal disease, therefore accurate identification of clinically significant proteinuria is essential to the diagnosis and management of kidney disease. Spot samples are now widely used, namely protein: creatinine ratio (uPCR) and albumin: creatinine ratio (uACR). In this article we review the evidence comparing uPCR and uACR including clinical, laboratory and financial arguments.

uPCR has a superior performance to uACR to predict 24-hour total proteinuria, the measurement on which the evidence for interventions in chronic kidney disease is based. Furthermore a retrospective study comparing uPCR and uACR as predictors of renal outcome found comparable performance to predict all-cause mortality, commencement of renal replacement therapy and doubling of serum creatinine. Only uPCR takes account of non-albumin proteinuria which has been shown to have prognostic significance. uACR was been thought to be superior at low levels (where there is less ‘noise’ from physiological urinary proteins), but uPCR has recently been shown to perform well at levels equivalent to <0.5 g/day (and even within the reference range) as a predictor of outcomes. uACR is measured using an immunoassay that may be technically superior, but is not without shortcomings (such as antigen excess) and is 2–10 times more expensive than uPCR.

The theories explaining the superiority of albumin are appealing. However, the available comparative data do not seem to support the theory. We cannot explain the disparity, but in science, if the data do not fit the existing theory, then maybe it's time for a new theory.

Microproteinuria during Opisthorchis viverrini infection: a biomarker for advanced renal and hepatobiliary pathologies from chronic opisthorchiasis

Approximately 680 million people are at risk of infection with Opisthorchis viverrini (OV) and Clonorchis sinensis, with an estimated 10 million infected with OV in Southeast Asia alone. While opisthorchiasis is associated with hepatobiliary pathologies, such as advanced periductal fibrosis (APF) and cholangiocarcinoma (CCA), animal models of OV infection show that immune-complex glomerulonephritis is an important renal pathology that develops simultaneously with hepatobiliary pathologies. A cardinal sign of immune-complex glomerulonephritis is the urinary excretion of immunoglobulin G (IgG) (microproteinuria). In community-based studies in OV endemic areas along the Chi River in northeastern Thailand, we observed that over half of the participants had urine IgG against a crude OV antigen extract (OV antigen). We also observed that elevated levels of urine IgG to OV antigen were not associated with the intensity of OV infection, but were likely the result of immune-complex glomerulonephritis as seen in animal models of OV infection. Moreover, we observed that urine IgG to OV antigen was excreted at concentrations 21 times higher in individuals with APF and 158 times higher in individuals with CCA than controls. We also observed that elevated urine IgG to OV antigen could identify APF+ and CCA+ individuals from non-cases. Finally, individuals with urine IgG to OV antigen had a greater risk of APF as determined by Odds Ratios (OR = 6.69; 95%CI: 2.87, 15.58) and a greater risk of CCA (OR = 71.13; 95%CI: 15.13, 334.0) than individuals with no detectable level of urine IgG to OV antigen. Herein, we show for the first time the extensive burden of renal pathology in OV endemic areas and that a urine biomarker could serve to estimate risk for both renal and hepatobiliary pathologies during OV infection, i.e., serve as a “syndromic biomarker” of the advanced pathologies from opisthorchiasis.

Approximately 680 million people risk infection with food-borne trematodes, including Opisthorchis viverrini (OV). Animal models show that significant kidney pathology results from OV infection as detected by antibodies in urine (microproteinuria). However, kidney pathology in humans infected with OV is often overlooked because it develops alongside more severe pathologies such as bile duct fibrosis and bile duct cancer. In Northeastern Thailand, the researchers observed that OV infected individuals had elevated levels of urine IgG against OV antigen that was not associated with the level of OV infection. The researchers observed that urine IgG to OV antigen was associated with bile duct fibrosis and bile duct cancer. Moreover, individuals with urine IgG to OV antigen also had elevated risk of bile duct fibrosis and bile duct cancer than individuals with no urine IgG to OV antigen. For the first time, OV infection has been shown to result in significant kidney disease in humans, which is also strongly associated with bile duct pathology. A urine-based assay that could indicate both renal and bile duct pathology from OV infection would be of profound benefit in Southeast Asia, especially in the resource-limited settings of the Mekong Basin region countries of Thailand, Laos and Cambodia.

Renal complications of Fabry disease in children

Fabry disease is an X-linked α-galactosidase A deficiency, resulting in accumulation of glycosphingolipids, especially globotriaosylceramide, in cells in different organs in the body. Renal failure is a serious complication of this disease. Fabry nephropathy lesions are present and progress in childhood while the disease commonly remains silent by routine clinical measures. Early and timely diagnosis of Fabry nephropathy is crucial since late initiation of enzyme replacement therapy may not halt progressive renal dysfunction. This may be challenging due to difficulties in diagnosis of Fabry disease in children and absence of a sensitive non-invasive biomarker of early Fabry nephropathy. Accurate measurement of glomerular filtration rate and regular assessment for proteinuria and microalbuminuria are useful, though not sensitive enough to detect early lesions in the kidney. Recent studies support the value of renal biopsy in providing histological information relevant to kidney function and prognosis, and renal biopsy could potentially be used to guide treatment decisions in young Fabry patients. This review aims to provide an update of the current understanding, challenges, and needs to better approach renal complications of Fabry disease in children.

Incidence and predictive value of proteinuria in community-acquired pneumonia

BACKGROUND/AIMS

The presence of baseline proteinuria predicts the outcome in patients with chronic kidney disease and in the general population, independent of renal function. However, the predictive value of proteinuria during an episode of acute illness has not been reported yet. Therefore, we investigated the incidence and predictive value of proteinuria in patients with community-acquired pneumonia.

METHODS

An analysis of prospectively collected data, obtained from patients >18 years of age, was performed. Patients were hospitalized with community-acquired pneumonia in two hospitals in the Netherlands and participated in two consecutive clinical trials. A total protein/creatinine (P/C) ratio was measured in a urine sample from the day of admission. Patients were categorized in quartiles of P/C ratio. Primary outcome was length of hospital stay.

RESULTS

198/319 patients (62%) had a P/C ratio >23 mg/mmol creatinine. In multivariate analysis, proteinuria turned out to be an independent predictor for length of stay and admission to the intensive care unit.

CONCLUSION

The incidence of proteinuria during pneumonia is high and proteinuria is an independent predictor for length of hospital stay and admission to the intensive care unit. Proteinuria is a cheap and easily accessible marker for outcome and might be used to assess the severity of pneumonia.

Urinary cystatin C and tubular proteinuria predict progression of diabetic nephropathy

OBJECTIVE

The aim of this study was to evaluate the association of urinary cystatin C, a tubular damage marker, with the progression of type 2 diabetic nephropathy. RESERCH DESIGN AND METHODS: The baseline values of serum and urinary cystatin C were measured as primary parameters and those of urinary nonalbumin protein (NAP) were measured as secondary parameters. In this prospective observational study, a total of 237 type 2 diabetic patients were followed up for 29 months (13-44 months).

RESULTS

Both the urinary cystatin C-to-creatinine ratio (CCR) and NAP-to-creatinine ratio (NAPCR) were significantly different according to the degree of albuminuria. Both markers had strongly positive correlations at baseline. After adjusting for several clinical factors, both urinary CCR and NAPCR had significant associations with the decline of the estimated glomerular filtration rate (eGFR) (r = 0.160, P = 0.021; r = 0.412, P < 0.001, respectively). Urinary CCR had positive correlations with the decline of eGFR in the subpopulation of patients with eGFR ≥60 mL/min/1.73 m(2). In patients with eGFR ≥60 mL/min/1.73 m(2) and normoalbuminuria, only urinary NAPCR showed a significant association with the decline of eGFR; urinary CCR did not. In multivariate regression analysis, the number of patients who progressed to chronic kidney disease stage 3 or greater was higher in those in the upper tertiles of both the urinary levels of cystatin C and NAP than in those in the lower tertiles.

CONCLUSIONS

The results of this study suggest that urinary cystatin C and NAP may be predictors of the progression of type 2 diabetic nephropathy.

Chronic kidney disease and measurement of albuminuria or proteinuria: a position statement

Optimal detection and subsequent risk stratification of people with chronic kidney disease (CKD) requires simultaneous consideration of both kidney function (glomerular filtration rate [GFR]) and kidney damage (as indicated by albuminuria or proteinuria). Measurement of urinary albuminuria and proteinuria is hindered by a lack of standardisation regarding requesting, sample collection, reporting and interpretation of tests. A multidisciplinary working group was convened with the goal of developing and promoting recommendations that achieve consensus on these issues. The working group recommended that the preferred method for assessment of albuminuria in both diabetic and non-diabetic patients is urinary albumin-to-creatinine ratio (UACR) measurement in a first-void spot urine specimen. Where a first-void specimen is not possible or practical, a random spot urine specimen for UACR is acceptable. The working group recommended that adults with one or more risk factors for CKD should be assessed using UACR and estimated GFR every 1-2 years, depending on their risk-factor profile. Recommended testing algorithms and sex-specific cut-points for microalbuminuria and macroalbuminuria are provided. The working group recommended that all pathology laboratories in Australia should implement the relevant recommendations as a vital component of an integrated national approach to detection of CKD.

Short-term change in kidney function and risk of end-stage renal disease

BACKGROUND

It is unclear what degree of change in the eGFR over a 1-year period indicates clinically significant progression, and whether this change adds additional information beyond that obtained by a single eGFR measure alone.

METHODS

We included 598 397 adults who had at least two outpatient eGFR measurements (at least 6 months apart) during 1-year accrual period in Alberta, Canada. Change in kidney function (using the first and last eGFR) was defined by change in kidney function category with confirmation based on percent (%) change in eGFR [(last eGFR - first eGFR)/first eGFR × 100]. The groups for change in kidney function were thus defined as: 'certain drop' (drop in CKD category with ≥25% decrease in the eGFR); 'uncertain drop' (drop in CKD category with <25% decrease in the eGFR); 'stable' (no change in CKD category); 'uncertain rise' (rise in CKD category with <25% rise in the eGFR) and 'certain rise' (rise in CKD category with ≥25% increase in the eGFR). Adjusted end-stage renal disease (ESRD) rates (per 1000 person-years) for each group of change in kidney function were calculated using Poisson regression. Adjusted risks of ESRD associated with change in kidney function, in reference to stable kidney function, were estimated.

RESULTS

Among the 598 397 participants, 74.8% (n = 447 570) had stable (no change in CKD category), 3.3% (n = 19 591) had a certain drop and 3.7% (n = 22 171) had a certain rise in kidney function. Participants who experienced a certain change in kidney function (both drop and rise) were older, more likely to be female, and had a higher prevalence of comorbidities, in comparison with those with stable kidney function. There were 1966 (0.3%) ESRD events over a median follow-up of 3.5 years. Compared with participants with stable kidney function, after adjustment for covariates, and the first eGFR measurement, those with certain drop had 5-fold increased risk of ESRD (HR: 5.11; 95% CI: 4.56-5.71), whereas those with an uncertain drop had 2-fold increased risk (HR: 2.13; 95% CI: 1.84-2.47). After adjustment for the eGFR and covariates at the last visit, neither a certain nor uncertain drop in the eGFR was associated with an increased ESRD risk. The ESRD risk associated with the last eGFR level, adjusted for the slope over time, were 2.89 (95% CI: 2.35-3.55), 10.98 (95% CI: 8.69-13.87), 35.20 (95% CI: 27.95-44.32) and 147.96 (116.92-187.23) for categories 2, 3a, 3b and 4, respectively, in reference to category 1.

CONCLUSIONS

A change in eGFR category accompanied by ≥25% decline (certain drop) is associated with increased ESRD risk. However, this elevated risk is captured by patient characteristics and eGFR at the last visit, suggesting that eGFR trajectories based on more than two serum creatinine measurements over a period longer than 1 year are required to determine ESRD risk and allow more reliable risk prediction.

Impact of remote location on quality care delivery and relationships to adverse health outcomes in patients with diabetes and chronic kidney disease

BACKGROUND

To investigate the relation of residence location, markers of good quality healthcare and adverse clinical outcomes in patients with diabetes and chronic kidney disease (CKD).

METHODS

We identified 31 337 individuals with diabetes and estimated glomerular filtration rate (eGFR) 15-59 mL/min/1.73 m(2) from a population-based cohort (n= 1 278 375) of adults with serum creatinine measured at least once during 2005 or 2006 in Alberta, Canada. The study population was classified into categories based on travel distance by road from residence location to the closest nephrologist: (0-50, 50.1-100, 100.1-200 and >200 km).

RESULTS

At follow-up, compared with those living within 50 km, remote dwellers were less likely to visit a nephrologist, less likely to have hemoglobin A1c and urinary albumin measured within 1 year of the index eGFR, and less likely to receive an angiotensin converting enzyme inhibitor, angiotensin receptor blocker or statin (all P < 0.0001). In adjusted models, compared with those with CKD (Stage 3 or 4) living within 50 km, the adjusted likelihood of all-cause hospitalization was [1.4 (95% confidence interval, CI, 1.3-1.6)], [1.3 (95% CI, 1.1-1.6)] and [1.3 (95% CI, 1.2-1.5)]-fold higher for patients living 50.1-100, 100.1-200 and >200 km away from a nephrologist, respectively (P < 0.0001). The hazard ratio of all-cause mortality increased with increasing distance: [1.07 (95% CI, 0.9-1.2)], [1.1 (95% CI, 0.9-1.2)] and [1.2 (95% CI, 1.0-1.4)], respectively (P < 0.0001).

CONCLUSIONS

Compared with those living closer to a nephrologist, remote dwellers with diabetes and CKD were less likely to receive recommended quality care, and more likely to experience adverse health outcomes.

Homelessness and CKD: a cohort study

BACKGROUND AND OBJECTIVES

This study examined the associations between homelessness and clinical outcomes of CKD among adults from the urban healthcare safety net.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This retrospective cohort study examined 15,343 adults with CKD stages 3-5 who received ambulatory care during 1996-2005 from the Community Health Network of San Francisco. Main outcome measures were time to ESRD or death and frequency of emergency department visits and hospitalizations.

RESULTS

Overall, 858 persons (6%) with CKD stages 3-5 were homeless. Homeless adults were younger, were disproportionately male and uninsured, and suffered from far higher rates of depression and substance abuse compared with adults with stable housing (P<0.001 for all comparisons). Over a median follow-up of 2.8 years (interquartile range=1.4-6.1), homeless adults experienced significantly higher crude risk of ESRD or death (hazard ratio=1.82, 95% confidence interval=1.49-2.22) compared with housed adults. This elevated risk was attenuated but remained significantly higher (adjusted hazard ratio=1.28, 95% confidence interval=1.04-1.58) after controlling for differences in sociodemographics, comorbid conditions, and laboratory variables. Homeless adults were also far more likely to use acute care services (median [interquartile range] number of emergency department visits was 9 [4-20] versus 1 [0-4], P<0.001) than housed counterparts.

CONCLUSIONS

Homeless adults with CKD suffer from increased morbidity and mortality and use costly acute care services far more frequently than peers who are stably housed. These findings warrant additional inquiry into the unmet health needs of the homeless with CKD to provide appropriate and effective care to this disadvantaged group.

One-year change in kidney function is associated with an increased mortality risk

BACKGROUND

Serum creatinine is routinely measured to estimate glomerular filtration rate (GFR). Long-term cohort studies report that death is a likelier outcome than progression to kidney failure. However, it is unclear how short-term changes in estimated GFR (eGFR) over a 1-year period relate to subsequent mortality risk.

METHODS

Using a provincial laboratory registry from Alberta, Canada, we identified 598,397 adults who had ≥2 outpatient eGFR measurements at least 6 months apart during a 1-year accrual period. Change in kidney function was categorized by both changes in eGFR category and percent change ≥25% into 5 groups: certain drop, uncertain drop, stable (no change in CKD category), uncertain rise, and certain rise. Cox proportional hazards models, adjusting for baseline covariates, kidney function, and proteinuria were used to estimate the risk of all-cause mortality associated with each group change in kidney function in reference to stable kidney function.

RESULTS

Among the study participants, 447,570 (74.8%) had stable kidney function, 19,591 (3.3%) had a certain drop, and 22,171 (3.7%) had a certain rise in kidney function. Participants with change in kidney function (both drop and rise) were older, more likely to be female, and had a higher prevalence of comorbidities in comparison to those with stable kidney function. There were 51,473 (8.6%) deaths during a median follow-up of 3.5 years. Compared to participants with stable kidney function, those with a certain drop had an almost twofold increased mortality risk (hazard ratio 1.89, 95% CI 1.83-1.95) adjusted for baseline eGFR, proteinuria, and covariates. Participants with a certain rise (3.7%) in kidney function also experienced an increased mortality risk (hazard ratio 1.51, 95% CI 1.46-1.56) compared to those with stable kidney function. Risk of death was similarly increased with adjustment for eGFR at the last visit.

CONCLUSION

Change in kidney function of ≥25% in any direction over a 1-year period is associated with a substantially increased risk of mortality.

[Advances in the prevention, diagnosis and therapy of vascular diseases]

Atherosclerosis is a systemic disease affecting the coronary, carotid, intracerebral, renal and peripherial arteries. The early morphological and functional impairments could be detected in the second or third decades of life and their progression depend on the number and severity of risk factors and individual susceptility. Although the vascular risk factors (smoking, overweight, age, unhealthy diet, lack of physical exercise, hypertension, diabetes mellitus, chronic kidney disease and dyslipidemia) are the same and common in the different vascular diseases, the present clinical routine artificially classifies the diagnosis and therapy of different vascular diseases into different subfields of medicine with the negative impact of possible polypragmasia. Recently, worldwide health surveys (e.g. REACH registry) have proven the usefulness of a holistic approach in the diagnosis and therapy of multiorgan-affected vascular patients. This review summarizes the multidisciplinary advances and future perspective of vascular diseases.

Simultaneous measurement of urinary albumin and total protein may facilitate decision-making in HIV-infected patients with proteinuria

OBJECTIVE

We recently showed that a urine albumin/total protein ratio (uAPR) <0.4 identifies tubular pathology in proteinuric patients. In tubular disorders, proteinuria is usually of low molecular weight and contains relatively little albumin. We tested the hypothesis that uAPR is useful in identifying tubular pathology related to antiretroviral use in HIV-infected patients.

METHODS

We retrospectively identified urine protein/creatinine ratios (uPCRs) in HIV-infected patients. A subset of samples had uPCR and urine albumin/creatinie ratio (uACR) measured simultaneously. We classified proteinuric patients (uPCR >30 mg/mmol) into two groups: those with predominantly 'tubular' proteinuria (TP) (uAPR <0.4) and those with predominantly 'glomerular' proteinuria (GP) (uAPR ≥ 0.4).

RESULTS

A total of 618 of 5244 samples from 1378 patients had uPCR ≥ 30 mg/mmol. uAPRs were available in 144 patients: 46 patients (32%) had TP and 21 (15%) GP; the remainder had uPCR <30 mg/mmol. The TP group had a higher fractional excretion of phosphate compared with the GP group (mean 27% vs. 16%, respectively; P<0.01). Patients with TP were more likely to be on tenofovir and/or a boosted protease inhibitor compared with those with GP. In 18 patients with heavy proteinuria (uPCR >100 mg/mmol), a renal assessment was made; eight had a kidney biopsy. In all cases, the uAPR results correlated with the nephrological diagnosis.

CONCLUSIONS

In HIV-infected patients, measuring uAPR may help to identify patients in whom a renal biopsy is indicated, and those in whom tubular dysfunction might be an important cause of proteinuria and which may be related to antiretroviral toxicity. We suggest that this would be useful as a routine screening procedure in patients with proteinuria.

What is the best method of proteinuria measurement in clinical trials of endothelin receptor antagonists?

AIMS

To determine whether protein-creatinine ratio (PCR) and albumin-creatinine ratio (ACR) are comparable to 24h urine protein in terms of agreement and repeatability, and therefore whether they are suitable for monitoring and comparing reduction in proteinuria in clinical trials of endothelin receptor antagonists.

MAIN METHODS

Using data from a recent study of sitaxentan in 27 patients with proteinuric chronic kidney disease, the assays were compared with reference to their agreement, repeatability, the number of measurements required to obtain accurate results and correlation with reduction in proteinuria at baseline.

KEY FINDINGS

The median coefficient of variation was lower for PCR than 24h urine protein (25 vs. 28%) but the range was higher (70 vs. 47%). When converted into the same units, mean difference between 24h urine protein and both PCR (0.03 g/day), and ACR (0.10 g/day), was small. However, scatter increased with mean level of proteinuria, such that agreement fell substantially above 1.5 g/day. According to 2-factor within-subjects ANOVA, the assay used was not a significant source of variation (PCR p=0.63, ACR p=0.38). With 3 measurements at each time point, baseline proteinuria correlated equally well with change in proteinuria, and percentage change was detected accurately by all 3 methods.

SIGNIFICANCE

PCR and ACR may well be suitable replacements for 24h urine protein in the clinical trial context due to their similar accuracy and repeatability, greater convenience and lower cost. However, a randomised control trial comparing all 3 assays in a larger and more diverse population is necessary before 24h urine protein can be replaced.

Endothelial nitric oxide synthase gene polymorphisms and the risk of diabetic nephropathy in type 2 diabetes mellitus

Endothelial dysfunction plays an important role in the pathogenesis of diabetic vascular disease, including diabetic nephropathy (DN). Endothelial nitric oxide synthase (eNOS) gene polymorphisms that affect eNOS activity are associated with endothelial dysfunction. The aim of this study was to evaluate the association of three polymorphisms of the eNOS gene (894G>T, -786T>C, and 27-bp-VNTR) with the risk of DN among type 2 diabetic patients. A total of 400 type 2 diabetic patients were enrolled in this study. The DN group comprised 200 patients; the group of diabetics without nephropathy comprised another 200 patients. Genetic analysis for eNOS gene polymorphisms was done in all subjects. Measurement of nitric oxide levels was estimated. The C allele for -786T>C and the T allele for 894G>T were significantly more frequent in diabetics with nephropathy than in diabetics without nephropathy (p<0.001; odds ratio [OR] and 95% confidence interval [CI] for the C allele=1.64 [1.24-2.17] and p<0.001; OR and 95% CI=1.7 [1.27-2.26] for the T allele). The haplotypes CTa (with all the mutant alleles) and CTb were significantly more common in patients with DN (p=0.01 and 0.003, respectively). These results suggested that the eNOS polymorphisms might represent genetic determinants for developing DN in type 2 diabetic Egyptians.

The value of simultaneous measurements of urinary albumin and total protein in proteinuric patients

BACKGROUND

Proteinuria is a common pathological finding in renal disease. Examining the urinary protein electrophoretic pattern gives clues to the site of origin of the protein. We hypothesized that the type of proteinuria, classified by urine protein electrophoresis and immunofixation (uPEI), may be predicted by simply examining the proportion of higher molecular weight protein (e.g. albumin) in urine total protein content.

METHODS

One thousand and eleven patients, whose urine had been sent to the pathology department for uPEI, were analysed for total protein and albumin to creatinine ratio (uPCR and uACR) and the ratio reported as the albumin to total protein ratio (uAPR). In a group of renal outpatients (n=248), we also specifically measured tubular proteins (N-acetyl-β-D-glucosaminidase, NAG, and β2-microglobulin) and expressed these as ratios to creatinine (uNCR and uβ2CR). To validate these findings, we correlated these measurements with 68 patients in whom we also had renal biopsy data.

RESULTS

In receiver operating characteristic (ROC) curve analysis, the AUC for uAPR was 0.84 for predicting tubular proteinuria pattern on uPEI. In the renal outpatient subgroup, uAPR predicted a tubular pattern of urinary protein equally as well as testing for specific tubular protein markers (uNCR and uβ2CR). In the validation cohort, a uAPR cut-off of <0.40 was 88% sensitive and 99% specific for the diagnosis of primary tubulointerstitial disorders on renal biopsy.

CONCLUSIONS

Useful information about the origins of urinary protein may be inferred by measuring uAPR, the measurement of which is both simple and inexpensive.

Association between GFR, proteinuria, and adverse outcomes among White, Chinese, and South Asian individuals in Canada

BACKGROUND

We investigated the association between proteinuria, estimated glomerular filtration rate (eGFR), and risk of mortality and kidney failure in white, Chinese, and South Asian populations.

STUDY DESIGN

Population-based cohort study.

SETTING & PARTICIPANTS

Participants from Alberta, Canada, with a serum creatinine and urine protein dipstick measurement from January 1, 2005, to December 31, 2005.

PREDICTOR

White, Chinese, or South Asian ethnicity.

OUTCOMES

Prevalence of proteinuria by level of eGFR (estimated using the MDRD [Modification of Diet in Renal Disease] Study equation) and the association between eGFR, proteinuria, and all-cause mortality and kidney failure.

MEASUREMENTS

Rates of all-cause mortality and kidney failure per 1,000 person-years were calculated using Poisson regression by ethnicity, eGFR level, and proteinuria level while adjusting for sociodemographic variables and comorbid conditions.

RESULTS

Of 491,729 participants, 5.3% were Chinese and 4.7% were South Asian. For participants with eGFR <60 mL/min/1.73 m(2), the prevalence of heavy proteinuria was higher in Chinese and South Asians compared with whites. Compared with whites, adjusted rates of death were significantly lower for Chinese and South Asian populations (rate ratios, 0.67 [95% CI, 0.56-0.80] and 0.73 [95% CI, 0.59-0.88], respectively); these rate ratios did not vary by eGFR and proteinuria levels.

LIMITATIONS

Using surname to identify ethnicity has the potential for misclassification due to name changes and identical last names from different ethnic groups. Also, to be eligible for inclusion, participants had to have a measurement of serum creatinine and urine dipstick proteinuria.

CONCLUSIONS

Although increasing proteinuria and lower eGFR predicted mortality and progression to kidney failure in all 3 ethnic groups, both Chinese and South Asian populations experienced a lower risk of death and similar risk of kidney failure compared with whites at all eGFR and proteinuria levels. Studies exploring this association further are required.

Increased urinary protein excretion in the "normal" range is associated with increased renin-angiotensin system activity

Increased levels of albuminuria and proteinuria, both linked to augmented renin-angiotensin system (RAS) activity, are associated with adverse kidney and cardiovascular events. However, the relationship between variations in urinary albumin excretion (UAE) and total protein excretion (UTPE) in the normal range and RAS activity is unclear. We examined the association between UAE and UTPE and the hemodynamic response to angiotensin II (ANG II) challenge, a well-accepted indirect measure of RAS activity, in healthy individuals with normal UAE and UTPE. Forty subjects (15 men, 25 women; age 38 ± 2 yr; UAE, 3.32 ± 0.55 mg/day; UTPE, 56.8 ± 3.6 mg/day) were studied in high-salt balance. Blood pressure (BP), arterial stiffness determined by applanation tonometry, and circulating RAS components were measured at baseline and in response to graded ANG II infusion. The primary outcome was the BP response to ANG II challenge at 30 and 60 min. UAE was associated with a blunted diastolic BP response to ANG II infusion (30 min, P = 0.005; 60 min, P = 0.17), a relationship which remained even after adjustment (30 min, P < 0.001; 60 min, P = 0.035). Similar results were observed with UTPE (30 min, P = 0.031; 60 min, P = 0.001), even after multivariate analysis (30 min, P = 0.008; 60 min, P = 0.001). Neither UAE nor UTPE was associated with systolic BP, circulating RAS components, or arterial stiffness responses to ANG II challenge. Among healthy individuals with UAE and UTPE in the normal range, increased levels of these measures were independently associated with a blunted diastolic BP response to ANG II, indicating increased vascular RAS activity, which is known to be deleterious to both renal and cardiac function.

Multiple versus single and other estimates of baseline proteinuria status as predictors of adverse outcomes in the general population

BACKGROUND

The association of proteinuria and adverse clinical outcomes is well established. The optimal method of classifying proteinuria status for study participants in whom it is measured multiple times is unknown, especially when the frequency of measurement varies between participants.

STUDY DESIGN

Population-based longitudinal study.

SETTING & PARTICIPANTS

All adults with at least one outpatient serum creatinine measurement in the province of Alberta, Canada.

FACTOR

Proteinuria (dipstick, albumin-creatinine ratio [ACR]).

OUTCOMES

All-cause mortality, end-stage renal disease, or doubling of serum creatinine level.

MEASURES

All outpatient urine dipstick and ACR measurements in the 6-month period before and after the first (index) estimated glomerular filtration rate were used to establish baseline proteinuria. Dipstick measures were analyzed as ceiling (median value up to the next integer), floor (median value down to the next integer), high (single highest dipstick value), low (single lowest dipstick value), and first (first available dipstick value only). Measurements of ACR were evaluated similarly and a median (median of all ACR measurements) value was added.

RESULTS

Of 920,985 participants, 17% (n = 160,548) had multiple dipstick urinalysis measurements and 22% (n = 22,814) had multiple ACR measurements. With single measurements, absolute rates of mortality and renal outcomes were lower in every proteinuria category compared with multiple measurements. In contrast, the relative increase in rate ratio was greater with increasing proteinuria in patients with single measurements compared with those with multiple measurements. In all classification systems evaluated, more severe proteinuria was associated with significantly higher rates of both outcomes (all P for trend <0.001).

LIMITATIONS

Lack of a gold standard for choosing between methods.

CONCLUSIONS

Rates of adverse outcomes related to multiple baseline proteinuria/albuminuria measurements were similar, independent of the measure of baseline proteinuria that was used to combine results. In contrast, discarding follow-up measurements and relying on only the first measurement led to lower estimates of absolute and relative risk for each proteinuria category.

Higher estimated glomerular filtration rates may be associated with increased risk of adverse outcomes, especially with concomitant proteinuria

The estimated glomerular filtration rate (eGFR) is a powerful predictor of adverse outcomes, but most attention has focused on studies in the setting of reduced eGFR. Here we tested whether patients with an eGFR higher than 60-89.9 ml/min per 1.73 m(2) could also be at elevated risk of adverse outcomes. Further, we tested whether concomitant proteinuria further increases the risk of outcomes among individuals with an eGFR equal to or above 90 ml/min per 1.73 m(2), as it does for those with reduced eGFR. Using data from a population-based outpatient laboratory data set of 1,526,437 patients, we measured adjusted associations between eGFR calculated by the modification of diet in renal disease equation, urine dipstick proteinuria, and adverse clinical outcomes. The adjusted risk of all-cause mortality was lowest at an eGFR of 60-74.9 ml/min per 1.73 m(2) (referent) and increased at both lower and higher levels of eGFR. Specifically, the hazard ratio of death was 3.7 and 1.8 among patients with an eGFR equal to or above 105 and 90-104.9 ml/min per 1.73 m(2), respectively, compared to the referent group. Similar results were seen when the CKD-EPI equation (sensitivity analyses) was used to assess eGFR. Higher levels of eGFR were not associated with the risk of kidney failure or myocardial infarction. Thus, the presence and severity of proteinuria was significantly associated with graded increases in the risk of clinical outcomes for both lower and higher eGFR. We do not know, however, whether the finding at higher eGFR could be due to inadequacies of the eGFR formula at low serum creatinine levels.

Urinary proteins, N-acetyl-β-D-glucosaminidase activity and estimated glomerular filtration rate in hypertensive patients with normoalbuminuria and microalbuminuria

BACKGROUND

The aim of the study was to assess novel candidate markers measured in the urine of normoalbuminuric and microalbuminuric patients (the urinary albumin-to-creatinine ratio < 30 mg/mmol) with essential hypertension to be used for early detection and assessment of progressive deterioration in renal function.

METHODS

Albumin, α-1-antitrypsin, orosomucoid, transferrin, retinol-binding protein and α-1-microglobulin concentrations and the NAG (N-acetyl-β-D-glucosaminidase) activity in the urine were evaluated in 102 hypertensive subjects with urinary albumin-to-creatinine ratio (uACR) < 30 mg/mmol. The estimated glomerular filtration rate (e-GFR) was calculated using the Modification of Diet in Renal Disease Study equation.

RESULTS

The decreasing e-GFR values in normo- and microalbuminuric patients with essential hypertension were accompanied by significant increases (P < 0.05) in the NAG activity and uACR value in the urine. The e-GFR significantly (P < 0.05) correlated with the NAG activity in the urine, but no association was observed with the urinary concentrations of any of the individual proteins (P > 0.05).

CONCLUSIONS

In normoalbuminuric and microalbuminuric patients with essential hypertension renal impairment measured by e-GFR is related to the increased urinary NAG activity and uACR rather than elevated concentrations of individual proteins. Urinary NAG activity and uACR value seem independently promising candidate markers for use in assessing progression of early renal impairment in patients with hypertension.

Assessment of proteinuria

Proteinuria is a strong predictor of adverse cardiovascular and kidney events, and an accurate assessment of proteinuria is important for the evaluation and management of CKD. Total urinary protein can be assessed using dipstick, precipitation, and electrophoresis methods. Urinary albumin, the predominant urinary protein in most proteinuric kidney diseases, can be assessed using an albumin-specific dipstick, immunochemical techniques, and size-exclusion high-performance liquid chromatography. Urine albumin may be immune-reactive, immune-unreactive, fragmented, and biochemically modified, and laboratory techniques have variable abilities to detect different types of albumin. Urine specimen for proteinuria assessment can either be obtained from a timed-collection or a spot urine sample. Spot urine protein- or albumin-to-creatinine ratios are preferred to a 24-hour urine sample in routine practice. Assessment of albuminuria rather than proteinuria is more clinically meaningful in patients with diabetic kidney disease, and proteinuria and albuminuria assessments both have a role in nondiabetic kidney disease and in general population screening. As measurement and sampling procedures for proteinuria assessment have yet not been standardized, it is important for physicians to be aware of different types of urinary proteins, albumins, laboratory techniques, and urine sampling methods.

Associations among estimated glomerular filtration rate, proteinuria, and adverse cardiovascular outcomes

BACKGROUND AND OBJECTIVES

Most studies of chronic kidney disease (CKD) and outcomes focus on mortality and ESRD, with limited data on other adverse outcomes. This study examined the associations among proteinuria, eGFR, and adverse cardiovascular (CV) events.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This was a population-based longitudinal study with patients identified from province-wide laboratory data from Alberta, Canada, between 2002 and 2007. Selected for this study from a total of 1,526,437 patients were 920,985 (60.3%) patients with at least one urine dipstick measurement and 102,701 patients (6.7%) with at least one albumin-creatinine ratio (ACR) measurement. Time to hospitalization was considered for one of four indications: congestive heart failure (CHF), coronary artery bypass grafting (CABG) or percutaneous coronary intervention (PCI), peripheral vascular disease (PVD), and stroke/transient ischemic attacks [TIAs] (cerebrovascular accident [CVA]/TIA).

RESULTS

After a median follow-up of 35 months, in fully adjusted models and compared with patients with estimated GFR (eGFR) of 45 to 59 ml/min per 1.73 m(2) and no proteinuria, patients with heavy proteinuria by dipstick and eGFR ≥ 60 ml/min per 1.73 m(2) had higher rates of CABG/PCI and CVA/TIA. Similar results were obtained in patients with proteinuria measured by ACR.

CONCLUSIONS

Risks of major CV events at a given level of eGFR increased with higher levels of proteinuria. The findings extend current data on risk of mortality and ESRD. Measurement of proteinuria is of incremental prognostic benefit at every level of eGFR. The data support use of proteinuria measurement with eGFR for definition and risk stratification in CKD.

High-normal albuminuria and risk of heart failure in the community

BACKGROUND

Albuminuria has been associated with cardiovascular risk, but the relationship of high-normal albuminuria to subsequent heart failure has not been well established.

STUDY DESIGN

Prospective observational study, the Atherosclerosis Risk in Communities (ARIC) Study.

SETTING & PARTICIPANTS

10,975 individuals free from heart failure were followed up from the fourth ARIC Study visit (1996-1998) through January 2006.

PREDICTOR

Urinary albumin-creatinine ratio (UACR), analyzed continuously and categorically as optimal (<5 mg/g), intermediate-normal (5-9 mg/g), high-normal (10-29 mg/g), microalbuminuria (30-299 mg/g), and macroalbuminuria (≥300 mg/g).

OUTCOMES & MEASUREMENTS

Incident heart failure was defined as a heart failure-related hospitalization or death. Cox proportional hazard models were used to calculate the HR of heart failure after adjustment for age, race, sex, estimated glomerular filtration rate (eGFR), and other cardiovascular risk factors.

RESULTS

Individuals were followed up for a median of 8.3 years and experienced 344 heart failure events. Compared with normal UACR, albuminuria was associated with a progressively increased risk of heart failure from intermediate-normal (adjusted HR, 1.54; 95% CI, 1.12-2.11) and high-normal UACR (adjusted HR, 1.91; 95% CI, 1.38-2.66) to microalbuminuria (adjusted HR, 2.49; 95% CI, 1.77-3.50) and macroalbuminuria (adjusted HR, 3.47; 95% CI, 2.10-5.72). Results were similar in secondary analyses of participants censored at the time of coronary heart disease event and along a range of eGFRs.

LIMITATIONS

UACR was measured as a single random sample.

CONCLUSIONS

Albuminuria is associated with subsequent heart failure, even in individuals with few cardiovascular risk factors and UACR within the normal range. Our results suggest that the association between albuminuria and heart failure may not be mediated fully by ischemic heart disease or kidney disease, measured using eGFR.

Diagnostic accuracy of urine dipsticks for detection of albuminuria in the general community

BACKGROUND

Urine dipsticks, an inexpensive accessible test for proteinuria, are widely advocated for mass screening; however, their diagnostic accuracy in the general community is largely unknown.

STUDY DESIGN

Evaluation of diagnostic test accuracy in a cross-sectional cohort.

SETTING & PARTICIPANTS

AusDiab, a representative survey of Australian adults 25 years and older (conducted in 1999/2000). Stratified cluster random sampling from 11,247 individuals participating in the biomedical examination; complete urinalysis data available for 10,944.

INDEX TEST

Urine dipsticks (Bayer Multistix), with a positive result defined as ≥1+ or trace or higher protein.

REFERENCE TEST

Albumin-creatinine ratio (ACR), measured on a random spot urine sample. Reference test positivity was defined as ACR ≥30 mg/g or ACR ≥300 mg/g.

RESULTS

Numbers of participants with ACR <30, 30-300, and ≥300 mg/g were 10,219 (93.4%), 634 (5.8%), and 91 (0.8%), respectively. The area under the receiver operating characteristic curve (AUC) for dipstick detection of ACR ≥30 mg/g was 0.8451 ± 0.0129 (SE) in men and 0.7775 ± 0.0131 in women (P < 0.001). The AUROC for dipstick detection of ACR ≥300 mg/g was 0.9904 ± 0.0030 in men and 0.9950 ± 0.0016 in women (P = 0.02). Dipstick result ≥1+ identified ACR ≥30 mg/g with 57.8% sensitivity (95% CI, 54.1%-61.4%) and 95.4% specificity (95% CI, 95.0%-95.8%) and identified ACR ≥300 mg/g with 98.9% sensitivity (99% CI, 92.1%-100%) and 92.6% specificity (99% CI, 92.0%-93.3%). A dipstick result of trace or higher identified ACR ≥30 mg/g with 69.4% sensitivity (95% CI, 65.9%-72.7%) and 86.8% specificity (95% CI, 86.1%-87.4%) and identified ACR ≥300 mg/g with 100% sensitivity (99% CI, 94.3%-100%) and 83.7% specificity (99% CI, 82.8%-84.6%). A negative dipstick result (less than trace) had a negative predictive value of 97.6% (95% CI, 97.2%-97.9%) for ACR ≥30 mg/g and a negative predictive value of 100% (99% CI, 99.9%-100%) for ACR ≥300 mg/g. The probability of an ACR ≥30 mg/g confirmed on laboratory investigation was 47.2% (95% CI, 43.9%-50.5%) based on a dipstick result ≥1+ and 27.1% (95% CI, 25.1%-29.2%) based on a trace or higher result.

LIMITATIONS

Isolated urine samples precluded assessment of test reproducibility. Urine specific gravity and pH were not recorded; therefore, the effect of urine concentration on test performance was not assessed.

CONCLUSIONS

A dipstick test result <1+ or less than trace has a high negative predictive value in the general community setting, with minimal risk of a missed diagnosis of macroalbuminuria. High false-positive rates emphasize the need for laboratory confirmation of positive results.