Biological Variability of Albumin Excretion Rate and Albumin-to-Creatinine Ratio in Hypertensive Type 2 Diabetic Patients

Urine Albumin-Creatinine Ratio Variability in People With Type 2 Diabetes: Clinical and Research Implications

RATIONALE & OBJECTIVE

Evidence has demonstrated that albuminuria is a key diagnostic and prognostic marker of diabetic chronic kidney disease, but the impact of its day-to-day variability has not been adequately considered. This study quantified within-individual variability of albuminuria in people with type 2 diabetes to inform clinical albuminuria monitoring.

STUDY DESIGN

Descriptive cross-sectional analysis.

SETTING & PARTICIPANTS

People with type 2 diabetes (n=826, 67.1 [IQR, 60.3-72.4] years, 64.9% male) participating in the Progression of Diabetic Complications (PREDICT) cohort study.

EXPOSURE

Four spot urine collections for measurement of urinary albumin-creatinine ratio (UACR) within 4 weeks.

OUTCOME

Variability of UACR.

ANALYTICAL APPROACH

We characterized within-individual variability (coefficient of variation [CV], 95% limits of random variation, intraclass correlation coefficient), developed a calculator displaying probabilities that any observed difference between a pair of UACR values truly exceeded a 30% difference, and estimated the ranges of diagnostic uncertainty to inform a need for additional UACR collections to exclude or confirm albuminuria. Multiple linear regression examined factors influencing UACR variability.

RESULTS

We observed high within-individual variability (CV 48.8%; 95% limits of random variation showed a repeated UACR to be as high/low as 3.78/0.26 times the first). If a single-collection UACR increased from 2 to 5mg/mmol, the probability that UACR actually increased by at least 30% was only 50%, rising to 97% when 2 collections were obtained at each time point. The ranges of diagnostic uncertainty were 2.0-4.0mg/mmol after an initial UACR test, narrowing to 2.4-3.2 and 2.7-2.9mg/mmol for the mean of 2 and 3 collections, respectively. Some factors correlated with higher (female sex; moderately increased albuminuria) or lower (reduced estimated glomerular filtration rate and sodium-glucose cotransporter 2 inhibitor/angiotensin-converting enzyme inhibitor/angiotensin receptor blocker treatment) within-individual UACR variability.

LIMITATIONS

Reliance on the mean of 4 UACR collections as the reference standard for albuminuria.

CONCLUSIONS

UACR demonstrates a high degree of within-individual variability among individuals with type 2 diabetes. Multiple urine collections for UACR may improve capacity to monitor changes over time in clinical and research settings but may not be necessary for the diagnosis of albuminuria.

PLAIN-LANGUAGE SUMMARY

Albuminuria (albumin in urine) is a diagnostic and prognostic marker of diabetic chronic kidney disease. However, albuminuria can vary within an individual from day to day. We compared 4 random spot urinary albumin-creatinine ratio (UACR) samples from 826 participants. We found that a second UACR collection may be as small as a fourth or as large as almost 4 times the first sample's UACR level. This high degree of variability presents a challenge to our ability to interpret changes in albuminuria. Multiple collections have been suggested as a solution. We have constructed tools that may aid clinicians in deciding how many urine collections are required to monitor and diagnose albuminuria. Multiple urine collections may be required for individual monitoring but not necessarily for diagnosis.

Long-term intra-individual variability of albuminuria in type 2 diabetes mellitus: implications for categorization of albumin excretion rate

BACKGROUND

Diabetic kidney disease (DKD) is the leading cause of end-stage renal disease in the Western world. Early and accurate identification of DKD offers the best chance of slowing the progression of kidney disease. An important method for evaluating risk of progressive DKD is abnormal albumin excretion rate (AER). Due to the high variability in AER, most guidelines recommend the use of more than or equal to two out of three AER measurements within a 3- to 6-month period to categorise AER. There are recognised limitations of using AER as a marker of DKD because one quarter of patients with type 2 diabetes may develop kidney disease without an increase in albuminuria and spontaneous regression of albuminuria occurs frequently. Nevertheless, it is important to investigate the long-term intra-individual variability of AER in participants with type 2 diabetes.

METHODS

Consecutive AER measurements (median 19 per subject) were performed in 497 participants with type 2 diabetes from 1999 to 2012 (mean follow-up 7.9 ± 3 years). Baseline clinical characteristics were collected to determine associations with AER variability. Participants were categorised as having normo-, micro- or macroalbuminuria according to their initial three AER measurements. Participants were then categorised into four patterns of AER trajectories: persistent, intermittent, progressing and regressing. Coefficients of variation were used to measure intra-individual AER variability.

RESULTS

The median coefficient of variation of AER was 53.3%, 76.0% and 67.0% for subjects with normo-, micro- or macroalbuminuria at baseline. The coefficient of variation of AER was 37.7%, 66% and 94.8% for subjects with persistent, intermittent and progressing normoalbuminuria; 43%, 70.6%, 86.1% and 82.3% for subjects with persistent, intermittent, progressing and regressing microalbuminuria; and 55.2%, 67% and 82.4% for subjects with persistent, intermittent and regressing macroalbuminuria, respectively.

CONCLUSION

High long-term variability of AER suggests that two out of three AER measurements may not always be adequate for the optimal categorisation and prediction of AER.

Paper-based assays for urine analysis

A transformation of the healthcare industry is necessary and imminent: hospital-centered, reactive care will soon give way to proactive, person-centered care which focuses on individuals' well-being. However, this transition will only be made possible through scientific innovation. Next-generation technologies will be the key to developing affordable and accessible care, while also lowering the costs of healthcare. A promising solution to this challenge is low-cost continuous health monitoring; this approach allows for effective screening, analysis, and diagnosis and facilitates proactive medical intervention. Urine has great promise for being a key resource for health monitoring; unlike blood, it can be collected effortlessly on a daily basis without pain or the need for special equipment. Unfortunately, the commercial rapid urine analysis tests that exist today can only go so far-this is where the promise of microfluidic devices lies. Microfluidic devices have a proven record of being effective analytical devices, capable of controlling the flow of fluid samples, containing reaction and detection zones, and displaying results, all within a compact footprint. Moving past traditional glass- and polymer-based microfluidics, paper-based microfluidic devices possess the same diagnostic ability, with the added benefits of facile manufacturing, low-cost implementation, and disposability. Hence, we review the recent progress in the application of paper-based microfluidics to urine analysis as a solution to providing continuous health monitoring for proactive care. First, we present important considerations for point-of-care diagnostic devices. We then discuss what urine is and how paper functions as the substrate for urine analysis. Next, we cover the current commercial rapid tests that exist and thereby demonstrate where paper-based microfluidic urine analysis devices may fit into the commercial market in the future. Afterward, we discuss various fabrication techniques that have been recently developed for paper-based microfluidic devices. Transitioning from fabrication to implementation, we present some of the clinically implemented urine assays and their importance in healthcare and clinical diagnosis, with a focus on paper-based microfluidic assays. We then conclude by providing an overview of select biomarker research tailored towards urine diagnostics. This review will demonstrate the applicability of paper-based assays for urine analysis and where they may fit into the commercial healthcare market.

Chronic kidney disease: Defining clinical cut-offs for albumin:creatinine ratio

Albuminuria is rapidly gaining recognition as a marker of the presence and of the progression of chronic kidney disease (CKD). In a new study, Naresh et al. attempt to define cut-off values for percentage change in urinary albumin:creatinine ratio that reflect changes in CKD status rather than random biological variation.

Evaluation of the Hypoglycemic Properties of Anacardium humile Aqueous Extract

The antihyperglycemic effects of several plant extracts and herbal formulations which are used as antidiabetic formulations have been described and confirmed to date. The main objective of this work was to evaluate the hypoglycemic activity of the aqueous extract of Anacardium humile. Although the treatment of diabetic animals with A. humile did not alter body weight significantly, a reduction of the other evaluated parameters was observed. Animals treated with A. humile did not show variation of insulin levels, possibly triggered by a mechanism of blood glucose reduction. Levels of ALT (alanine aminotransferase) decreased in treated animals, suggesting a protective effect on liver. Levels of cholesterol were also reduced, indicating the efficacy of the extract in reestablishing the balance of nutrients. Moreover, a kidney protection may have been achieved due to the partial reestablishment of blood glucose homeostasis, while no nephrotoxicity could be detected for A. humile. The obtained results demonstrate the effectiveness of A. humile extracts in the treatment of alloxan-induced diabetic rats. Therefore, A. humile aqueous extract, popularly known and used by diabetic patients, induced an improvement in the biochemical parameters evaluated during and following treatment of diabetic rats. Thus, a better characterization of the medicinal potential of this plant will be able to provide a better understanding of its mechanisms of action in these pathological processes.

Monitoring young people with type 1 diabetes for diabetic nephropathy: potential errors of annual ACR testing

AIM

Type 1 diabetes guidelines recommend annual monitoring of albumin-creatinine ratio (ACR) to detect nephropathy. Annual monitoring for conditions such as dyslipidemia leads to high rates of false-positive diagnoses. We estimated rates of false-positive and false-negative diagnoses under annual, biennial and triennial monitoring.

METHODS

Using Oxford Regional Prospective Study (ORPS) data we modelled ACR over time. Using simulation we estimated numbers of positive and negative diagnoses and the proportion that are false, over 6 years of monitoring, when assessment intervals are 1, 2 or 3 years.

RESULTS

Average increase per year (95%C.I.) in ACR was 3,5% (2,0-5,0%) for males and 4,8% (3,2-6,5%) for females. By 6 years, annual monitoring would lead to 56 (49-63) false-positive diagnoses for every 100 positive diagnoses of micro-albuminuria, biennial to 49 (42-57) false-positives and triennial to 46 (39-53). For every 100 negative diagnoses, annual monitoring would lead to 1,2 (0,8-1,5) false-negatives, biennial to 2,3 (1,7-3,0) and triennial to 3,0 (2,2-3,8).

CONCLUSION

Less frequent monitoring would result in fewer false-positive diagnoses, but increased false negatives, or missed diagnoses. The clinical implications of these scenarios need further investigation through cost-benefit analysis.

Urine analysis in microfluidic devices

Microfluidics has attracted considerable attention since its early development in the 1980s and has experienced rapid growth in the past three decades due to advantages associated with miniaturization, integration and automation. Urine analysis is a common, fast and inexpensive clinical diagnostic tool in health care. In this article, we will be reviewing recent works starting from 2005 to the present for urine analysis using microfluidic devices or systems and to provide in-depth commentary about these techniques. Moreover, commercial strips that are often treated as chips and their readers for urine analysis will also be briefly discussed. We start with an introduction to the physiological significance of various components or measurement standards in urine analysis, followed by a brief introduction to enabling microfluidic technologies. Then, microfluidic devices or systems for sample pretreatments and for sensing urinary macromolecules, micromolecules, as well as multiplexed analysis are reviewed, in this sequence. Moreover, a microfluidic chip for urinary proteome profiling is also discussed, followed by a section discussing commercial products. Finally, the authors' perspectives on microfluidic-based urine analysis are provided. These advancements in microfluidic techniques for urine analysis may improve current routine clinical practices, particularly for point-of-care (POC) applications.

High normal levels of albuminuria and risk of hypertension in Indo-Asian population

BACKGROUND

Urine albumin excretion in the high normal range [urine albumin to creatinine ratio (UACR) 10-29 mg/g)] predicts hypertension in European-origin populations. However, the prognostic significance of UACR in the high normal range for incident hypertension is unclear in Indo-Asians. The objective of this study was to examine the relationship of normal to high normal levels of UACR and incident hypertension.

METHODS

We conducted a nested cohort study within a cluster randomized controlled trial in Pakistan on 1272 normotensive non-diabetic adults aged ≥ 40 years with UACR <30 mg/g. Incident hypertension was defined as new onset of systolic blood pressure (SBP) ≥ 140 mmHg or diastolic ≥ 90 mmHg or initiation of antihypertensive therapy.

RESULTS

A total of 920 (72.3%) participants completed the 2-year final follow-up. During this time, 105 (11.4%) developed incident hypertension. In the multivariable model, the odds [95% confidence interval (CI)] for incident hypertension were 2.45(1.21-4.98) for those in the fourth (top) quartile (≥ 6.1 mg/g) and 2.12 (1.04-4.35) in the third quartile (3.8-6.1 mg/g) compared to those in the lowest quartile (<2.8 mg/g). In addition, a significant interaction between UACR and baseline SBP was observed suggesting that the odds (95% CI) of incident hypertension with UACR were greater at lower baseline SBP (interaction P = 0.044).

CONCLUSIONS

High normal levels of albuminuria as measured by UACR predict hypertension in non-diabetic Indo-Asians, and this relationship may be enhanced in individuals with low baseline SBP. Further research is needed to assess the clinical applicability of these findings.

Gender-specific reference value of urine albumin-creatinine ratio in healthy Chinese adults: results of the Beijing CKD survey

BACKGROUND

The reference value of urine albumin-creatinine ratio (ACR) has racial disparities. The ACR reference value in a healthy Beijing population is reported.

METHODS

A reference Beijing population was sampled via a multistage, clustered complex sampling method. By excluding subjects with self-reported kidney disease, hypertension, diabetes, dyslipidemia, cardiovascular disease, obesity or underweight condition, overt proteinuria, hematuria, or pyuria, as well as those with an estimated glomerular filtration rate (eGFR) > 200ml/min/1.73m2 or < 60ml/min/1.73m2, apparently healthy subjects (1260 males, 2305 females, aged 18-84y) were selected to be included in the current analysis. Urine albumin was measured using the immunoturbidimetic method, creatinine was measured using Jaffe's kinetic method on a morning spot-urine sample, and ACR was calculated. The 95th percentile of ACR was used as the normal upper limit. The association between ACR and each of gender, age, systolic blood pressure, body mass index, serum glucose, lipids, and eGFR was examined.

RESULTS

The normal upper limit of ACR was 14mg/g (1.58mg/mmol) for males and 20mg/g (2.26mg/mmol) for females. Females had higher ACR values than males, and age, systolic blood pressure, and eGFR were positively correlated with ACR.

CONCLUSIONS

The ACR reference value in the healthy Beijing population is lower than that of the Western population. Age, systolic blood pressure, and eGFR were found to correlate with ACR.

High prevalence of albuminuria in population-based patients diagnosed with type 2 diabetes in the Shanghai downtown

OBJECTIVE

The prevalence of albuminuria and the risk factors associated with albuminuria were evaluated among the Chinese patients diagnosed with type 2 diabetes aged over 30 in the Shanghai downtown. We also evaluated the variability of urinary albumin-to-creatinine ratio (ACR) among the three measurements and the relationship between diabetic retinopathy (DR) and albuminuria.

METHODS

The 1039 Chinese patients diagnosed with type 2 diabetes aged over 30 were investigated by randomized cluster sampling in the Shanghai downtown and 1018 patients were analyzed in this study. Body mass measurements including height, weight, waist circumference and hip circumference, resting blood pressure, fasting blood measures, urinary ACR and the digitally stored fundus images were investigated. The prevalence of albuminuria was calculated and the risk factors associated with albuminuria were evaluated by stepwise logistic regression. The concordance of urinary ACR was evaluated by observed agreement. The relationship between albuminuria and DR was also evaluated.

RESULTS

(1) The mean age of all patients was 66.10+/-11.54 years and the duration of diabetes was 7.89+/-7.16 years. (2) The prevalence of albuminuria was 49.6% among the Chinese patients diagnosed with type 2 diabetes aged over 30 in the Shanghai downtown, 41.4% with microalbuminuria and 8.2% with macroalbuminuria. (3) Microalbuminuria was significantly associated with systolic blood pressure, gender and waist circumference. Macroalbuminuria was significantly associated with systolic blood pressure and duration of diabetes. (4) Observed agreement among the three urinary ACR measurement for albuminuria staging was 73.3% (first versus second), 64.5% (first versus third) and 77.5% (second versus third). Observed agreement in the albuminuria staging between the single urinary ACR measurement and all three urinary ACR measurements was 85.8% (first versus all three), 87.6% (second versus all three) and 81.9% (third versus all three). (5) The percentage of DR in the macroalbuminuric group (59.2%) was significantly higher than that in the normalbuminuria group (16.1%) and microalbuminuria group (24.6%). (6) The macroalbuminuric patients with DR had significantly increased fasting blood glucose and HbA1c compared with the macroalbuminuric patients without DR.

CONCLUSION

The prevalence of microalbuminuria observed in the Chinese patients diagnosed with type 2 diabetes aged over 30 in the Shanghai downtown reached up to 41.4% though the observations in our study might be representative of the diabetic patients of the Shanghai downtown. We agreed that at least two of the three urinary collections were done in a 3- to 6-month period because of the day-to-day variability in albumin excretion. The percentage of DR among the patients with macroalbuminuria was 59.2%, and the macroalbuminuric patients with the significantly high plasma glucose and DR were prone to diagnose DN.

Albumin excretion rate is not affected by asymptomatic urinary tract infection: a prospective study

OBJECTIVE

The aim of the study was to evaluate whether asymptomatic urinary tract infection (UTI) significantly influences the level of albumin excretion rate (AER) in diabetic patients.

RESEARCH DESIGN AND METHODS

We screened prospectively for UTI and AER in 765 type 2 diabetic subjects. AER was determined before and after antimicrobial therapy in those patients in whom an asymptomatic UTI was diagnosed (n = 59). To interpret the clinical significance of AER changes, the coefficient of biological variation (CVb) of the AER (CVb-AER) was assessed in a control group of type 2 diabetic patients without UTI (n = 56).

RESULTS

AER did not change after antimicrobial treatment either in the whole group of patients with UTI (pre: 13.8 microg/min [0.1-195] vs. post: 8.5 microg/min [0.1-185]; P = 0.1) or in those patients in whom the infection was eradicated (pre: 11.7 microg/min [0.1-195] vs. post: 7.1 microg/min [0.1-185]; NS). The CVb-AER was 64% in the control group and was inversely correlated with AER (r = -0.44; P = 0.001). The decrease of AER after antimicrobial therapy (55%) did not exceed the biological variation of AER (64%). Finally, UTI did not significantly influence the classification of diabetic patients as normo- or microalbuminuric.

CONCLUSIONS

Asymptomatic UTI does not increase AER in type 2 diabetic patients. Therefore, our results suggest that testing for UTI is not necessary when AER is measured in diabetic patients.