Underestimation of urinary albumin to creatinine ratio in morbidly obese subjects due to high urinary creatinine excretion

Change in albuminuria as a surrogate endpoint for cardiovascular and renal outcomes in patients with diabetes

For the purpose of predicting clinical outcomes in patients with diabetes and chronic kidney disease, change in albuminuria is a good candidate to be a surrogate marker for future cardiovascular events and progression of kidney disease. Spot urine albumin/creatinine ratio is convenient and recognized as a viable alternative to 24-h albumin, with some limitations. Although there is sufficient evidence to validate its use in clinical trials as a surrogate endpoint for renal outcomes, this is not yet the case for cardiovascular outcomes. While change in albuminuria as a primary or secondary endpoint is trial-specific, its use should be encouraged, nonetheless.

Risk of sarcopenia among older persons with Type 2 diabetes mellitus with different status of albuminuria: A dose-responsive association

BACKGROUND

The association between type 2 diabetes mellitus (T2DM) and sarcopenia has been reported before, but little was known regarding associations between albuminuria status in the development of sarcopenia. This study aimed to explore the associations between albuminuria status and sarcopenia among older patients with T2DM.

METHODS

This cross-sectional study recruited T2DM patients aged 65 years and older from the DM shared care center in a regional hospital who were grossly absent from functional impairment. Demographic characteristics were collected and functional assessments were performed for all participants. Urinary albumin-to-creatinine ratio (UACR) was obtained by spot urine exams, whereas UACR ≥ 30 mg/g was defined as microalbuminuria, and UACR > 300 mg/g as macroalbuminuria. Appendicular lean mass (ASM) was measured by the dual X-ray absorptiometry, and the relative appendicular muscle mass (RASM) was calculated as the ASM divided by height square (kg/m²).The definition of sarcopenia was made according to the Asian Working Group for Sarcopenia and muscle quality was defined as handgrip strength (kg) divided by RASM.

RESULTS

Overall, 180 participants (mean age: 72.5±5.3 years, 53.3% males) were enrolled for study. Higher HbA1c levels and poorer renal function were significantly associated with more severe albuminuria status.Besides, sarcopenia and low handgrip strength also showed dose-responsive associations with albuminuria status, which was similar in muscle quality.The receiver operating characteristic curve determine that the UACR of 13.7 mg/g was the optimal cutoff for sarcopenia diagnosis, which was lower than the conventionally definition of microalbuminuria (<30 mg/g).

CONCLUSIONS

Albuminuria status was dose-responsively associated with sarcopenia among older persons with T2DM, and the risk started to escalate from minimal albuminuria (UACR 9.18 mg/g in men and 18.4 mg/g in women). Further intervention studies are needed to evaluate potential benefits of better diabetes control in preventing sarcopenia and its outcomes.

Addressing the problem of inaccuracy of measured 24-hour urine collections due to incomplete collection

The 24-hour urine collection is widely considered the gold standard for assessing 24-hour excretion of various analytes. Yet, studies show that >30% of collections are incomplete and hence understate the true 24-hour excretion. We previously validated an equation for estimating an individual's 24-hour creatinine excretion, based on weight, sex, race, and age. The present study examines whether routinely correcting measured 24-hour excretion of an analyte using the ratio of estimated to measured 24-hour urine creatinine mitigates the misleadingly low values that result from undercollection. Ninety-nine participants, recruited from an outpatient hypertension clinic, submitted a 24-hour urine collection for measurement of creatinine and sodium excretion. The urine collections were dichotomized into complete (n = 63) and incomplete (n = 36) collections based on previously described criteria for expected 24-hour creatinine excretion. To adjust for possible incompleteness of collections, the measured 24-hour values were then corrected by multiplying them by the ratio of estimated to measured 24-hour urine creatinine. The mean 24-hour creatinine excretion was 1682 mg/d among complete collectors. Among incomplete collectors, the mean was 1211 mg/d before and 1695 mg/d after, adjustment. Similarly, mean 24-hour sodium excretion was 156 mEq/d among complete collectors, whereas among incomplete collectors it was 121 mEq/d before and 171 mEq/d after, adjustment. Undercollection of 24-hour urines is a common problem and results in misleadingly low values for excretion of analytes being measured. Routine adjustment of 24-hour urine values using estimated values for 24-hour creatinine excretion can greatly mitigate artifactually low 24-hour excretion results.

Urinary Proteomics for Diagnosis and Monitoring of Diabetic Nephropathy

The last decade has seen a surge in publications describing novel biomarkers for early detection of diabetic nephropathy (DN), but as yet none have outperformed albuminuria in well-designed prospective studies. This is partially attributable to our incomplete understanding of the many complex interrelated mechanisms underlying DN development, a heterogeneous process unlikely to be captured by a single biomarker. Proteomics offers the advantage of simultaneously analysing the entire protein content of a biological sample, and the technique has gained attention as a potential tool for a more accurate diagnosis of disease at an earlier stage as well as a means by which to unravel the pathogenesis of complex diseases such as DN using an untargeted approach. This review will discuss the potential of proteomics as both a clinical and research tool, evaluating exploratory work in animal models as well as diagnostic potential in human subjects.

Relationship Between Sarcopenia and Albuminuria: The 2011 Korea National Health and Nutrition Examination Survey

Studies have shown that albuminuria, obesity, and sarcopenia may share pathophysiological processes related to cardiovascular disease risk. Their direct relationships, however, have not been examined. This study investigated the association between albuminuria and sarcopenia in a representative fraction of the Korean population.Of the 10,589 people who participated in the 2011 Korea National Health and Nutrition Examination Survey, 2158 participants aged over 19 years had been tested for albumin-to-creatinine ratio and for body composition data using dual-energy x-ray absorptiometry. Albuminuria was defined as an albumin-to-creatinine ratio ≥30 mg/g. Sarcopenia was defined as a skeletal muscle index (SMI) (SMI (%) = total appendicular skeletal muscle mass [kg]/weight [kg] × 100) of less than 1 standard deviation (SD) (grade 1) or 2 SD (grade 2) below the sex-specific mean for a younger reference group.The prevalence of albuminuria was higher in those with grade 2 sarcopenia than in those with a normal SMI or grade 1 sarcopenia (33.3% versus 8.4% and 8.9%; P < 0.001). Conversely, grade 2 sarcopenia was also more prevalent in participants with albuminuria than in those with the upper tertile of normoalbuminuria. In addition, multiple logistic regression analysis showed the odds ratio for albuminuria risk in the grade 2 sarcopenia group was 2.93 (95% confidence interval [CI], 1.46-5.88), compared with normal SMI after adjusting for potential confounding factors, including the presence of obesity, diabetes, and hypertension. Moreover, individuals with albuminuria had an odds ratio of 3.39 (95% [confidence interval], 1.38-8.37) for grade 2 sarcopenia compared with those in the lowest tertile of normoalbuminuria.This is the first study to demonstrate that individuals with sarcopenia exhibited increased risk of albuminuria and vice versa.

A New Gender-Specific Formula to Estimate 24-Hour Urine Protein from Protein to Creatinine Ratio

<b><i>Background:</i></b> The quantification of proteinuria with the protein to creatinine ratio (PCR) is influenced by the excretion of creatinine, which, in turn, varies according to muscle mass and hence, to gender. <b><i>Aims:</i></b> To assess the difference between urine PCR and 24-hour urine proteinuria in men and women and to provide a formula to overcome bias caused by gender. <b><i>Methods:</i></b> Four hundred and forty four CKD patients were randomly divided into 2 groups: 70% were used to develop the models, while the remaining 30% were reserved to validate the formula. Epidemiological data were analyzed with chi-square and Student's t tests. Association between 24-hour proteinuria and PCR was studied with Spearman coefficient in men and women separately. Multivariate analysis was used to find variables predictive of disagreement between the 24-hour urine protein and the PCR. Equations to predict 24-hour proteinuria from PCR for men and women were plotted and validated. <b><i>Results:</i></b> Disagreement between 24-hour proteinuria and PCR was more pronounced in men (2.16 and 1.64 g in mean, respectively) than in women (2.00 and 2.06 g in mean, respectively). Age and gender were independent predictors of disagreement. Gender-specific equations for predicting 24-hour proteinuria were: males: 24-hour proteinuria = 1.3350*exp^0.9108*^ln(PCR); females: 24-hour proteinuria = 1.0068*exp^0.9030*^ln(PCR). <b><i>Conclusions:</i></b> Estimation of proteinuria with the PCR improves accuracy if gender-specific equations are used. Use of the PCR without correction for gender leads to the underestimation of proteinuria in men and overestimation in women.

The incidence of albuminuria after bariatric surgery and usual care in Swedish Obese Subjects (SOS): a prospective controlled intervention trial

BACKGROUND

Obesity is associated with increased risk of chronic kidney disease and albuminuria is a predictor of renal impairment. Bariatric surgery reduces body weight in obese subjects, but it is not known whether surgery can prevent development of albuminuria. This study aims to determine the long-term effect of bariatric surgery on the incidence of albuminuria.

SUBJECTS

The Swedish Obese Subjects study is a non-randomized, prospective, controlled study conducted at 25 public surgical departments and 480 primary health care centers in Sweden. Between 1 September 1987 and 31 January 2001, 2010 participants who underwent bariatric surgery and 2037 controls were recruited. Inclusion criteria were age 37-60 years and BMI ⩾ 34 in men and BMI ⩾ 38 in women. In this analysis, we included 1498 patients in the surgery group and 1610 controls without albuminuria at baseline. Patients in the bariatric surgery group underwent banding (18%), vertical banded gastroplasty (69%) or gastric bypass (13%); controls received usual obesity care. Date of analysis was 1 January 2011. Median follow-up was 10 years, and the rates of follow-up were 87%, 74 and 52% at 2, 10 and 15 years, respectively. The main outcome of this report is incidence of albuminuria (defined as urinary albumin excretion >30 mg per 24 h) over up to 15 years.

RESULTS

During the follow-up, albuminuria developed in 246 participants in the control group and in 126 in the bariatric surgery group, corresponding to incidence rates of 20.4 and 9.4 per 1000 person years, respectively (adjusted hazard ratio, 0.37; 95% confidence interval, 0.30-0.47; P < 0.001). The expected number of surgeries needed to prevent the development of albuminuria in one patient at 10 years was nine.

CONCLUSIONS

Bariatric surgery is associated with reduced incidence of albuminuria compared with usual obesity care.