Which method for quantifying urinary albumin excretion gives what outcome? A comparison of immunonephelometry with HPLC

Cobalt oxide modified sulfur and phosphorus Co-doped g-C3N4 for screening of urinary human albumin

The fabrication of a heteroatom-doped nanocomposite based on cobalt oxide modified sulfur, phosphorus co-doped carbon nitride (Co3O4/SP-CN) with increased active sites is reported. The synthesized nanocomposite offers surprisingly high electrocatalytic oxidation efficacy toward human albumin (HA) despite its agglomeration. This improved efficacy of Co3O4/SP-CN nanocomposite could be attributed to its increased adsorption sites and surface defects, fast charge transportation capability, and conductivity. Additionally, morphological and compositional analysis of the fabricated Co3O4/SP-CN material has been performed  through scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photon spectroscopy (XPS), and Raman spectroscopy. The fabricated electrode shows remarkable amperometric response against the HA with a limit of detection of 8.39 nM and linear range of 20-4000 nM at applied potential of 0.25 V versus Ag/AgCl in 0.1 M PBS (pH 8.2). The designed Co3O4/SP-CN electrode has been successfully applied to monitor HA in  urine samples of diabetic patient with recovery percentage from 94.1 and 92.1% and with relative standard deviation (RSD) values of 5.8 and 7.8%. According to the best of our knowledge, this is the first report to use a Co3O4/SP-CN-based graphitic pencil (GP) electrode for monitoring of HA for early diagnosis of diabetic nephropathy.

Comparison of Microalbuminuria Status in Type 2 Diabetes Mellitus Patients With Chronic Periodontitis: A Cross-Sectional Study

Background

Diabetes has increased the risk for various other ailments in various organs of the body. This can be contributing to periodontitis also as it is the sixth complication related to diabetes mellitus. There is a bidirectional relationship between both. Given the high global prevalence of type-2 diabetes mellitus (T2DM) with periodontitis, it is of great importance to determine the link between periodontitis and microalbuminuria in T2DM patients, which shows early renal disease.

Methodology

In the present study, a total of 500 patients having T2DM were assessed for periodontitis using Community Periodontal Index (CPI). Anthropometric and biochemical measurements were obtained. Blood samples were estimated for glycemic control tests such as fasting plasma glucose (FPG), glycated hemoglobin (HbA1c), and lipid profile. The subjects who participated in the study were categorized into three groups depending on the albuminuria level. The data were tabulated and analyzed using SPSS Statistics software (IBM Corp., Armonk, USA).

Results

Out of 500 T2DM subjects, 342 subjects had periodontitis. A statistically significant difference was found in FPG, HbA1c, total cholesterol (TC), triglycerides, and low-density lipoprotein (LDL) between subjects with periodontitis and without periodontitis using a t-test (p = <0.001). The prevalence of normoalbuminuria, micro-, and macroalbuminuria among periodontitis patients was 24.6%, 72.8%, and 2.6% respectively, and the Chi-square analysis revealed that was highly significant. In terms of albuminuria, one-way analysis of variance (ANOVA) revealed statistically significant differences among the periodontitis subjects for the following variables: inputs such as the number of teeth, diabetes mellitus (DM) duration, the level of LDL, and also the depth of the pocket. Intergroup comparison of variables among subjects with albuminuria using the statistical test of Tukey Post Hoc found that there is a significant difference between normoalbuminuria and microalbuminuria. CPI score, tooth mobility, smoking, education level, family income, tooth brushing duration, along with the use of other dental hygiene aids was also found to be statistically significant among subjects with periodontitis.

Conclusion

The study concluded that T2DM patients had a higher incidence of microalbuminuria among individuals with periodontitis. These subjects also had significantly higher HbA1c and FPG levels than subjects with normoalbuminuria. In addition, subjects with periodontitis exhibited a significant reduction in the total teeth numbers present in the case of albuminuria. The longitudinal correlation between DM, microalbuminuria, and periodontitis could be further investigated in detail to explore possible pathways.

Connection between the Plasma Level of Apelin and Diabetic Nephropathy in Type 2 Diabetic Patients. A Case Control Study

BACKGROUND

Apelin is an adipokine that may have an advantageous role in the prediction of early diabetic nephropathy. A few studies on apelin in diabetes have been performed and this research was performed to establish the connection between the apelinergic system and diabetic nephropathy.

MATERIALS AND METHODS

The research included 60 patients with type 2 diabetes mellitus (T2DM) who were equally divided into Group-I (diabetic nephropathy) and Group-II (non-diabetic nephropathy), and 30 healthy subjects in the control group (Group-III). Body mass index (BMI) and waist circumference were calculated. FBG, 2 h-PPG, HbA1c, fasting lipids, urea, creatinine, eGFR, urine analysis, A/C ratio, and apelin levels were assessed.

RESULTS

A statistically significant between-group difference in plasma apelin levels was found (P < 0.001). Apelin was the highest in Group-I than in Group-II relative to Group-III (325.79 ± 59.42 pg/mL, 162.83 ± 29.88 pg/mL, and 77.43 ± 8.44 pg/mL, respectively). Among diabetic patients, plasma apelin had a significantly positive correlation with disease duration (r = 0.612), SBP (r = 0.427), DBP (r = 0.466), weight (r = 0.372), and height (r = 0.372), FBG (r = 0.684), 2 h-PPG (r = 0.744), HbA1C (r = 0.890), total (T)-cholesterol (r = 0.316), low density lipoprotein (LDL)-C (r = 0.397), urea (r = 0.575), and creatinine (r = 0.591). A significantly negative correlation was observed between plasma apelin and HDL-C (r = -0.303), and eGFR (r = -0.566).

CONCLUSION

Apelin levels in diabetics were elevated in the case of nephropathy, impaired glucose tolerance, and dyslipidemia. This supports the relationship between the apelinergic system and diabetic nephropathy.

Protein-templated copper nanoclusters for fluorimetric determination of human serum albumin

Copper nanoclusters (CuNCs) are attractive for their unique optical properties, providing sensitive fluorescent detection of several kinds of targets even in complex matrices. Their ability in growing on suitable protein and nucleic acid templates make CuNCs efficient optical reporters to be exploited in bioanalysis. In this work, we report the specific and sensitive determination of human serum albumin (HSA) in human serum (HS) and urine via CuNCs fluorescence. HSA is the most abundant protein in plasma, and plays a key role in the early diagnosis of serious pathological conditions such as albuminuria and albuminemia. Recently, HSA has become clinically central also as a biomarker to assess severity, progression, and prognosis of various cancers. We report the controlled and reproducible growth of CuNCs directly on the target analyte, HSA, which results in a fine dose-dependent fluorescent emission at 405 nm. The protocol is optimized in water, and then applied to serum and urine specimens, without matrix pretreatment. The method linearly responds within the whole concentration of clinical interest, with a sensitivity of 1.8 ± 0.1 × 10^-3 g L^-1 and 0.62 ± 0.03 × 10^-3 g L^-1 in serum and urine, respectively, and excellent reproducibility (CV_av% ca. 3% for both). The assay is designed to have a single protocol working for both matrices, with recovery of 95% (HS) and 96% (urine). The stability of the fluorescence after CuNCs formation was tested over 3 days, displaying good results (yet higher in urine than in serum).

Review: Detection and quantification of proteins in human urine

Extensive medical research showed that patients, with high protein concentration in urine, have various kinds of kidney diseases, referred to as proteinuria. Urinary protein biomarkers are useful for diagnosis of many health conditions - kidney and cardio vascular diseases, cancers, diabetes, infections. This review focuses on the instrumental quantification (electrophoresis, chromatography, immunoassays, mass spectrometry, fluorescence spectroscopy, the infrared spectroscopy, and Raman spectroscopy) of proteins (the most of all albumin) in human urine matrix. Different techniques provide unique information on what constituents of the urine are. Due to complex nature of urine, a separation step by electrophoresis or chromatography are often used for proteomics study of urine. Mass spectrometry is a powerful tool for the discovery and the analysis of biomarkers in urine, however, costs of the analysis are high, especially for quantitative analysis. Immunoassays, which often come with fluorescence detection, are major qualitative and quantitative tools in clinical analysis. While Infrared and Raman spectroscopies do not give extensive information about urine, they could become important tools for the routine clinical diagnostics of kidney problems, due to rapidness and low-cost. Thus, it is important to review all the applicable techniques and methods related to urine analysis. In this review, a brief overview of each technique's principle is introduced. Where applicable, research papers about protein determination in urine are summarized with the main figures of merits, such as the limit of detection, the detectable range, recovery and accuracy, when available.

Immune-unreactive urinary albumin as a predictor of cardiovascular events: the Hortega Study

BACKGROUND

We aimed to determine if immune-unreactive albumin excretion (IURAE) is associated with cardiovascular (CV) events in a representative sample of a general population from Spain.

METHODS

We included 1297 subjects (mean age ± standard error 48.0 ± 0.2 years, 48% females), who participated in the Hortega Follow-Up Study. The primary endpoint was incidence of fatal and non-fatal CV events. Urinary albumin excretion (UAE) was measured in spot voided urine, frozen at -80°C, by immunonephelometry [immune-reactive albumin excretion (IRAE)] and by high-performance liquid chromatography (HPLC) [total albumin excretion (AE)]. IURAE was calculated as the difference between HPLC measurements and IRAE. We estimated fully adjusted hazard ratios (HRs) of CV incidence by Cox regression for IRAE, IURAE and total AE.

RESULTS

After an average at-risk follow-up of 13 years, we observed 172 CV events. urinary albumin to creatinine ratio (UACR) of ≥30 mg/g assessed by IRAE, IURAE or total AE concentrations was observed in 74, 273 and 417 participants, respectively. Among discordant pairs, there were 49 events in those classified as micro- and macroalbuminuric by IURAE, but normoalbuminuric by IRAE. Only the IRAE was a significant independent factor for the incidence of CV events [HR (95% confidence interval) 1.15 (1.04-1.27)]. The association of UAE with CV events was mainly driven by heart failure (HF) [HR 1.33 (1.15-1.55) for IRAE; HR 1.38 (1.06-1.79) for IURAE; HR 1.62 (1.22-2.13) for total AE]. Those subjects who were micro- and macroalbuminuric by both IRAE and IURAE had a significant increase in risk for any CV event, and especially for HF.

CONCLUSIONS

IRAE, IURAE and AE were associated with an increased risk for CV events, but IRAE offered better prognostic assessment.

Methods of albumin estimation in clinical biochemistry: Past, present, and future

Estimation of serum and urinary albumin is routinely performed in clinical biochemistry laboratories. In the past, precipitation-based methods were popular for estimation of human serum albumin (HSA). Currently, dye-binding or immunochemical methods are widely practiced. Each of these methods has its limitations. Research endeavors to overcome such limitations are on-going. The current trends in methodological aspects of albumin estimation guiding the field have not been reviewed. Therefore, it is the need of the hour to review several aspects of albumin estimation. The present review focuses on the modern trends of research from a conceptual point of view and gives an overview of recent developments to offer the readers a comprehensive understanding of the subject.

Determination of Urine Albumin by New Simple High-Performance Liquid Chromatography Method

BACKGROUND

A simple high-performance liquid chromatography (HPLC) method was developed for the determination of albumin in patients' urine samples without coeluting proteins and was compared with the immunoturbidimetric determination of albumin. Urine albumin is important biomarker in diabetic patients, but part of it is immuno-nonreactive.

METHODS

Albumin was determined by high-performance liquid chromatography (HPLC), UV detection at 280 nm, Zorbax 300SB-C3 column. Immunoturbidimetric analysis was performed using commercial kit on automatic biochemistry analyzer COBAS INTEGRA^® 400, Roche Diagnostics GmbH, Manheim, Germany.

RESULTS

The HLPC method was fully validated. No significant interference with other proteins (transferrin, α-1-acid glycoprotein, α-1-antichymotrypsin, antitrypsin, hemopexin) was found. The results from 301 urine samples were compared with immunochemical determination. We found a statistically significant difference between these methods (P = 0.0001, Mann-Whitney test).

CONCLUSION

New simple HPLC method was developed for the determination of urine albumin without coeluting proteins. Our data indicate that the HPLC method is highly specific and more sensitive than immunoturbidimetry.

Urinary Albumin Detection: Comparison of Two Different Methods

BACKGROUND

Monitoring urinary albumin is a useful method in clinical practice for the management of diabetic nephropathy, chronic kidney disease, and hypertension. Currently there are neither standardized methods nor reference material for the determination of urinary albumin; for this reason it is useful to compare different assays used in clinical laboratory.

OBJECTIVES

The aim of this study is to verify analytical performance of an immunoturbidimetric assay on Roche Cobas 8000 platform and to compare urinary albumin results with those obtained by immunonephelometry on Siemens Dade Behring BN II Nephelometer.

RESULTS

The method comparison showed a good linear relationship, confirmed by Passing-Bablok and Bland-Altman plots. The turbidimetric assay meets the requirements of accuracy and precision for the practice of medical diagnostics and clinical use.

CONCLUSIONS

The present study can contribute to the methods standardization and harmonization of urinary albumin assay.

Markers of and risk factors for the development and progression of diabetic kidney disease

Diabetic kidney disease (DKD) occurs in 25%-40% of patients with diabetes. Given the dual problems of a significant risk of progression from DKD to end-stage renal disease (ESRD) and increased cardiovascular morbidity and mortality, it is important to identify patients at risk of DKD and ESRD and initiate protective renal and cardiovascular therapies. The importance of preventive therapy is emphasized further by worldwide increases in the incidence of diabetes. This review summarizes the evidence regarding the prognostic value and benefits of targeting established and novel risk markers for DKD development and progression. Family history of DKD, smoking history, and glycemic, blood pressure, and plasma lipid level control are established factors for identifying people at greatest risk of DKD development and progression. Absolute albumin excretion rate (AER) and glomerular filtration rate (GFR) measurements also are important, although AER categorization generally lacks the necessary specificity and sensitivity, and estimates of declining GFR are compromised by methodological limitations for GFRs in the normal-to-high range. Emerging risk markers for progressive loss of kidney function include markers of oxidation and inflammation, profibrotic cytokines, uric acid, advanced glycation end products, functional and structural markers of vascular dysfunction, kidney structural changes, and tubular biomarkers. Among these, the most promising are serum uric acid and soluble tumor necrosis factor receptor (type 1 and type 2) levels, especially in relation to GFR changes. At present, these can only be considered as risk markers because they only identify an individual at increased risk of progressive DKD and not necessarily related to the causal pathway promoting kidney damage. Further work is needed to establish whether modulating these factors improves the prognosis in DKD. Although change in urinary peptidome levels also is a promising marker, there currently is neither a clinical assay nor adequate studies defining its prognostic value. Until these or other novel markers become available for clinical use, predictive accuracy often may be increased with greater attention to established markers.

Prevalence and associated factors of microalbuminuria in Chinese individuals without diabetes: cross-sectional study

OBJECTIVE

To investigate the prevalence of microalbuminuria (MAU) among Chinese individuals without diabetes and the relationship between MAU and metabolic factors, individual socioeconomic status (SES), and regional economic development level.

DESIGN

Cross-sectional study of prevalence of MAU.

SETTING

152 urban street districts and 112 rural villages from northeast, north, east, south central, northwest and southwest China.

PARTICIPANTS

46 239 participants were recruited using a multistage stratified sampling design from 2007 to 2008. A total of 41 290 participants without diabetes determined by oral glucose tolerance test were included in the present study. Urine albumin/creatinine ratio results of 35 430 individuals were available.

PRIMARY AND SECONDARY OUTCOME MEASURES

Positive detection of MAU was determined using an ACR of 22.1-299.9 mg/g in men 30.9-299.9 mg/g in women.

RESULTS

The prevalence of MAU in men was 22.4% and 24.5% in women. In developed, intermediate-developed and under-developed areas, the prevalence of MAU in men was 20.7%, 21.9% and 32.5%, respectively; in women the prevalence was 19.6%, 26.0% and 29.5%, respectively. The prevalence of MAU increased as the number of metabolic disorders present increased, and as the number of lower SES components increased (farmer, below university education level and low income). Prevalence of MAU in developed and intermediate developed areas had adjusted risk ratios of 0.52 (95% CI 0.42 to 0.60) and 0.65 (95% CI 0.57 to 0.76), respectively. Multivariate logistic analyses demonstrated MAU was strongly associated with older age, high-blood pressure, higher blood glucose low education level, low occupational level and residence in under-developed region.

CONCLUSIONS

Several factors had independent correlations to MAU in China: older age, metabolic abnormalities, lower SES level and living in economically under-developed areas, which encourage the development of strategies to lower the risk for MAU in these susceptible populations.

The impacts of albuminuria and low eGFR on the risk of cardiovascular death, all-cause mortality, and renal events in diabetic patients: meta-analysis

BACKGROUND

Precise effects of albuminuria and low estimated glomerular filtration rate (eGFR) on cardiovascular mortality, all-cause mortality, and renal events in diabetic patients are uncertain.

MATERIALS AND METHODS

A systematic review was conducted of the literature through MEDLINE, EMBASE, and CINHAL from 1950 to December 2010. Cohort studies of diabetic patients providing adjusted relative risk (RR) of albuminuria and eGFR for risks of cardiovascular mortality, all-cause mortality, and renal events were selected. Two reviewers screened abstracts and full papers of each study using standardized protocol.

RESULTS

We identified 31 studies fulfilling the criteria from 6546 abstracts. With regard to the risk of cardiovascular mortality, microalbuminuria (RR 1.76, 95%CI 1.38-2.25) and macroalbuminuria (RR 2.96 95%CI 2.44-3.60) were significant risk factors compared to normoalbuminuria. The same trends were seen in microalbuminuria (RR 1.60, 95%CI 1.42-1.81), and macroalbuminuria (RR 2.64, 95%CI 2.13-3.27) for the risk of all-cause mortality, and also in microalbuminuria (RR 3.21, 95%CI 2.05-5.02) and macroalbuminuria (RR 11.63, 95%CI 5.68-23.83) for the risk of renal events. The magnitudes of relative risks associated with low eGFR along with albuminuria were almost equal to multiplying each risk rate of low eGFR and albuminuria. No significant factors were found by investigating potential sources of heterogeneity using subgroup analysis.

CONCLUSIONS

High albuminuria and low eGFR are relevant risk factors in diabetic patients. Albuminuria and low eGFR may be independent of each other. To evaluate the effects of low eGFR, intervention, or race, appropriately designed studies are needed.

Portable-Surface Plasmon Resonance Biosensor Immunoassays for the Human Serum Albumin Detection

The screening of urine human serum albumin (HSA) is significant for the early diagnosis and intervention of the nephropathia. This study developed sensitive HSA detection assay with a self-made portable-SPR biosensor based on the reflection light intensity interrogation. Anti-HSA monoclonal antibody was immobilized onto the gold sensing area and a directive assay for HSA was developed. A detection range of 1–100μg/mL HSA was found. The described label-free, real-time immunoassay for the quantification of HSA in urine is a rapid, sensitive, alternative method available for the clinic detection.

Methodological evaluation and comparison of five urinary albumin measurements

BACKGROUND

Microalbuminuria is an indicator of kidney damage and a risk factor for the progression kidney disease, cardiovascular disease, and so on. Therefore, accurate and precise measurement of urinary albumin is critical. However, there are no reference measurement procedures and reference materials for urinary albumin.

METHODS

Nephelometry, turbidimetry, colloidal gold method, radioimmunoassay, and chemiluminescence immunoassay were performed for methodological evaluation, based on imprecision test, recovery rate, linearity, haemoglobin interference rate, and verified reference interval. Then we tested 40 urine samples from diabetic patients by each method, and compared the result between assays.

RESULTS

The results indicate that nephelometry is the method with best analytical performance among the five methods, with an average intraassay coefficient of variation (CV) of 2.6%, an average interassay CV of 1.7%, a mean recovery of 99.6%, a linearity of R=1.00 from 2 to 250 mg/l, and an interference rate of <10% at haemoglobin concentrations of <1.82 g/l. The correlation (r) between assays was from 0.701 to 0.982, and the Bland-Altman plots indicated each assay provided significantly different results from each other.

CONCLUSION

Nephelometry is the clinical urinary albumin method with best analytical performance in our study.

Immunochemically unreactive albumin in urine: fiction or reality?

Urinary albumin measurements are currently not standardized due to a lack of a reference method and reference (primary and secondary [matrix]) material. Multiple molecular forms of albumin in urine are identified. Modification of albumin by proteolysis during passage through the urinary tract and chemical modification during specimen storage leads to the formation of albumin fragments. Multiple methods have been developed to quantify albuminuria and significant different results are reported dependent on the available assay. The current point of view of the National Kidney Disease Education Program - IFCC Working Group on Standardization of Albumin considers the immunoassay with polyclonal sera as the primary method of quantifying urine albumin. This article reviews the process of albumin fragmentation and focuses on the controversial topic of immuno-unreactive, nonimmunoreactive, or immunochemically nonreactive albumin fractions and its consequences for albumin analysis. We conclude that at present there are no hard arguments for measuring immunochemically unreactive albumin in urine. Immunoassays using polyclonal antisera for the detection of urinary albumin remain the gold standard. The development of a reference measurement procedure remains one of the challenges for the future.

Microalbuminuria in the paediatric age: current knowledge and emerging questions

The prevalence of microalbuminuria (MA) in children and adolescents differs from the one in adults, and it is estimated to be about 5.7-7.3% in boys and 12.7-15.1% in girls. The percentage is greater in smaller age group, whereas a positive association is found between albumin excretion rate and pubertal development stage in nondiabetic subjects. The data so far suggest that impairment of glucose metabolism, obesity-related proatherosclerotic pathways and the impact of haemodynamic load constitute major determinants of albuminuria development in the early years of life. In everyday practice if persistent MA is present at a young age, especially in the setting of diabetes, further investigation of cardiovascular risk factors, a more careful follow-up and dietary/lifestyle interventions are needed.

CONCLUSION

Although the significance of MA in paediatric essential hypertension has yet to be determined, its role in diabetic children and adolescents is established and albuminuria assessment has been utilized as a screening test for the presence of diabetes-related kidney disease.

Development of a colloidal gold-based immunochromatographic test strip for screening of microalbuminuria

A rapid immunochromatography (ICG) assay based on antibody colloidal gold nanoparticles specific to human serum albumin (HSA) was developed, and its applications for primary screening of HSA in the urine were evaluated. A monoclonal antibody (MAb) specific to HSA was produced from cloned hybridoma cells (EMRC1) and used to develop an ICG strip. The nanocolloidal gold, with an average particle diameter of 20 nm, was synthesized and labeled MAb as the detection reagent. An antibody colloidal gold probe was applied on the conjugate pad, and HSA antigen was immobilized to a nitrocellulose membrane as the capture reagent to prepare the ICG strip test. This test required only 10 min to accomplish a semiquantitative detection of albumin. The sensitivity to urinary albumin was found to be approximately 20 μg/mL, and the analytical range was 20-25 μg/mL. The reliability of the testing procedures was examined by carrying out the ICG strip test with 40 urine samples and comparing the results of these tests with those obtained via immunoturbidimetry. The ICG strip was adequately sensitive and accurate for a rapid screening of HSA in the urine.

Clinical implications of the early detection of urinary microalbumin in diabetic patients using a new high performance liquid chromatography (HPLC) method

We assessed urine albumin in 180 diabetics by conventional immunonephelometry (IN) and HPLC methods. Those with HPLC but not IN detectable albuminuria had higher BP, worse glycaemic control and more vascular events (p<0.05 for all) but received fewer vascular risk reduction treatments.

Cardiovascular risk factor treatment targets and renal complications in high risk vascular patients: a cohort study

BACKGROUND

To determine if recommended treatment targets, as specified in clinical practice guidelines for the management of cardiovascular disease, reduces the risk of renal complications in high risk patient populations.

METHODS

This was a cohort study. Participants in Utrecht, The Netherlands either at risk of, or had cardiovascular disease were recruited. Cardiovascular treatment targets were achievement of control in systolic and diastolic blood pressure, total and low-density cholesterol, and treatment of albuminuria. Outcome measures were time to development of end stage renal failure or symptomatic renal atherosclerotic disease requiring intervention.

RESULTS

The cohort consisted of 7,208 participants; 1,759 diabetics and 4,859 with clinically manifest vascular disease. The median age was 57 years and 67% were male. Overall, 29% of the cohort achieved the treatment target for systolic blood pressure, 39% for diastolic blood pressure, 28% for total cholesterol, 31% for LDL cholesterol and 78% for albuminuria. The incidence rate for end stage renal failure and renal atherosclerotic disease reduced linearly with each additional treatment target achieved (p value less than 0.001). Achievement of any two treatment targets reduced the risk of renal complications, hazard ratio 0.46 (95% CI 0.26-0.82). For patients with clinically manifest vascular disease and diabetes, the hazard ratios were 0.56 (95% CI 0.28 - 1.12) and 0.28 (95%CI 0.10 - 0.79) respectively.

CONCLUSION

Clinical guidelines for cardiovascular disease management do reduce risk of renal complications in high risk patients. Benefits are seen with attainment of any two treatment targets.

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.

Glomerular hemodynamics and arterial function in normal individuals

OBJECTIVE

To determine the relationship between arterial function (stiffness and wave reflection) and glomerular hemodynamics.

METHODS

In 49 healthy normotensive individuals, glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were measured by urinary clearances of 99mTC-DTPA and 131I-hippuran, respectively. Filtration fraction was computed as GFR/ERPF. Arterial stiffness was estimated by carotid-femoral pulse wave velocity (PWV). Wave reflection was evaluated by carotid augmentation index (AIx), reflection magnitude and the round-trip travel time of the pressure wave.

RESULTS

PWV and round-trip travel time were not independently correlated with any renal hemodynamic parameter or urinary albumin-creatinine ratio (UACR). AIx and reflection magnitude were directly correlated with filtration fraction (r = 0.35 and 0.37, respectively) and UACR (r = 0.43 and 0.53, respectively). When the population was divided into quartiles of reflection magnitude, filtration fraction and UACR progressively increased from the lowest to the highest quartile and after adjustment for age, mean arterial pressure, heart rate but also sex for UACR (P linear trend = 0.031 and 0.001, respectively).

CONCLUSION

It is suggested that in normal individuals, the amplitude of wave reflection but not arterial stiffness is associated with signs evocative of increased glomerular pressure (filtration fraction and UACR), independently of systemic blood pressure.

Potential urinary biomarkers of disease activity in Crohn's disease

OBJECTIVE

Measurement of the immunoreactive urinary albumin (ir-uAlb) concentration by immunological methods was found to be an effective method to identify disease activity in Crohn's disease (CD). Recently a size-exclusion (SE) high performance liquid chromatography (HPLC) method was developed to measure both ir-uAlb and non-immunoreactive urinary albumin (total, t-uAlb). We aimed to follow-up one of our CD patients with frequent remissions and exacerbation phases comparing the changes of disease activity parameters and the concentration of ir-uAlb and t-uAlb. The surprising results led us to perform measurements in greater depth.

MATERIAL AND METHODS

Concentration of ir-uAlb was measured by immunoturbidimetry (IT) and t-uAlb by SE-HPLC. Albumin peak of SE-HPLC was collected and applied to a reversed-phase (RP) HPLC and to gel-electrophoresis. Eluted peaks of RP-HPLC and identified bands of gel-electrophoresis were analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS).

RESULTS

The concentration of t-uAlb was 15 times higher than that of the ir-uAlb during active state. The RP-HPLC and the gel-electrophoresis separation proved that albumin peak by size-exclusion consists of three different peaks. MALDI-TOF/MS measurements identified α1-acid-glycoprotein and Zn-α2-glycoprotein as major, and albumin as minor protein.

CONCLUSIONS

Peak of albumin of SE-HPLC contains a significant amount of glycoprotein during the active phase of CD, which could not be detected in remission. Urinary α1-acid-glycoprotein and/or Zn-α2-glycoprotein could be an ideal disease activity biomarker of CD.

Combination of 1H nuclear magnetic resonance spectroscopy and liquid chromatography/mass spectrometry with pattern recognition techniques for evaluation of metabolic profile associated with albuminuria

A method using 1H NMR and LC/MS with pattern recognition tools such as principal component analysis (PCA) and orthogonal projection to latent structure discriminant analysis (O-PLS-DA) was used to study the urinary metabolic profiles associated with an increase in urinary albumin in a general population. The normalized peak intensities obtained from 1H NMR and LC/MS with nonparametric two-tailed Mann-Whitney analysis was used for the identification of network of potential biomarkers corresponding to the increase of albumin in urine. The specificity of detecting the stated metabolites by 1H NMR and LC/MS was demonstrated. Our preliminary data obtained demonstrated that LC/MS may produce more distinctive metabolic profiles. For the patient group, changes in alanine, kyneurnic acid, and xanthurenic acid might be associated with changes in the tryptophan metabolism. At the same time, other metabolites that were involved in citric acid cycle, amino acid metabolism, and cellular functions were affected in the patient group. The proposed approach provided a comprehensive picture of the metabolic changes induced by the increase of protein in urine and demonstrated the advantages of using multiple diagnostic biomarkers. At the same time, the current work was demonstrated as a potential cost-effective solution of high-throughput analysis with pattern recognition tools as applied here in a real clinical situation.

Diabetic nephropathy

Diabetic nephropathy is the leading cause of chronic renal disease and a major cause of cardiovascular mortality. Diabetic nephropathy has been categorized into stages: microalbuminuria and macroalbuminuria. The cut-off values of micro- and macroalbuminuria are arbitrary and their values have been questioned. Subjects in the upper-normal range of albuminuria seem to be at high risk of progression to micro- or macroalbuminuria and they also had a higher blood pressure than normoalbuminuric subjects in the lower normoalbuminuria range. Diabetic nephropathy screening is made by measuring albumin in spot urine. If abnormal, it should be confirmed in two out three samples collected in a three to six-months interval. Additionally, it is recommended that glomerular filtration rate be routinely estimated for appropriate screening of nephropathy, because some patients present a decreased glomerular filtration rate when urine albumin values are in the normal range. The two main risk factors for diabetic nephropathy are hyperglycemia and arterial hypertension, but the genetic susceptibility in both type 1 and type 2 diabetes is of great importance. Other risk factors are smoking, dyslipidemia, proteinuria, glomerular hyperfiltration and dietary factors. Nephropathy is pathologically characterized in individuals with type 1 diabetes by thickening of glomerular and tubular basal membranes, with progressive mesangial expansion (diffuse or nodular) leading to progressive reduction of glomerular filtration surface. Concurrent interstitial morphological alterations and hyalinization of afferent and efferent glomerular arterioles also occur. Podocytes abnormalities also appear to be involved in the glomerulosclerosis process. In patients with type 2 diabetes, renal lesions are heterogeneous and more complex than in individuals with type 1 diabetes. Treatment of diabetic nephropathy is based on a multiple risk factor approach, and the goal is retarding the development or progression of the disease and to decrease the subject's increased risk of cardiovascular disease. Achieving the best metabolic control, treating hypertension (<130/80 mmHg) and dyslipidemia (LDL cholesterol <100 mg/dl), using drugs that block the renin-angiotensin-aldosterone system, are effective strategies for preventing the development of microalbuminuria, delaying the progression to more advanced stages of nephropathy and reducing cardiovascular mortality in patients with diabetes.

Early detection of microalbuminuria and hypertension in children of very low birthweight

OBJECTIVE

We retrospectively investigated a cohort of very low birthweight infants (VLBWI) by comparing two methods for assessment of albuminuria: nephelometry (standard) and high performance liquid chromatography (HPLC), measuring urinary immunoreactive and non-immunoreactive albumin to evaluate if the latter is more sensitive in identifying childhood onset of albuminuria and hypertension in VLBWI individuals.

METHODS

Spot urine samples of a total of 109 subjects (5.3 +/- 2.2 years old) who were VLBWI were investigated by HPLC and nephelometry. Twenty-eight subjects were small for gestational age (SGA) and 81 were appropriate for gestational age (AGA). Blood Pressure (BP) was also recorded.

RESULTS

Twelve children (11%) with albuminuria 20 mg/g Cr by nephelometry versus 48 (44.5%) by HPLC (p < 0.001) were identified. The mean +/- SD of values in the range of normoalbuminuria was 2.9 +/- 5.81 by nephelometry versus 22.6 +/- 14 for HPLC (p < 0.001). The values were not statistically different in the two birthweight categories (<1000, 1000-1499 g), in AGA versus SGA and in high BP (>90th percentile) versus normal BP children.

CONCLUSIONS

Microalbuminuria by HPLC was more marked in VLBWI than in adults and the difference between values using the two methods was significative.

Albuminuria: what can we expect from the determination of nonimmunoreactive albumin?

Albuminuria is an early marker for diabetic nephropathy in patients with diabetes, and has a clear place in patient care. It also predicts cardiovascular events and mortality in diabetic patients and in the general population, and is slowly becoming accepted in population screening for cardiovascular disease and chronic kidney disease. Recently, investigators found that a considerable amount of albumin in urine is nonimmunoreactive and that classic immunochemical assays do not properly measure all albumin in urine. Assays that detect immunoreactive plus nonimmunoreactive albumin may better predict development of diabetic nephropathy, cardiovascular events, and mortality than assays that only detect immunoreactive albumin. Proof of the existence of nonimmunoreactive albumin emerged from the finding that albumin contains urine fragments. In this review, we critically appraise the presence and relevance of albumin fragments and nonimmunoreactive albumin molecules in urine, and the potential additive value of albuminuria detected by assays that assess nonimmunoreactive plus immunoreactive albumin over albuminuria detected by classic immunochemical assays in predicting end points.

[Early detection of diabetic nephropathy]

Due to the unfavorable prognosis of advanced stages of diabetic nephropathy (DN), the ideal approach is to identify renal involvement as early as possible. It is recommended to measure urinary albumin excretion (UAE) annually, in random urine samples, in order to detect the stages of DN [microalbuminuria (UAE 17-174 mg/l or 30-300 mg albumin/g of creatinine) and macroalbuminuria (> 174 mg/l or > 300 mg/g)]. However, it has been suggested that UAE levels below the threshold of consensus could already signal the risk for DN progression and increased mortality, indicating the need to revise cutoff values. As a substantial amount of UAE (the immunounreactive fraction), is not detected by conventional methods, HPLC would be more sensitive to identify the presence of damage by measuring total UAE (immunoreactive + immunounreactive). Another recent observation is that diminished glomerular filtration rates (GFR) occurs in the presence of normoalbuminuria. Therefore, besides evaluating UAE, it is recommended to estimate GFR with equations employing creatinine; such as the Modification of Diet in Renal Disease (MDRD) study, available at www.mdrd.com. Owing to the known limitations of creatinine, alternative endogenous markers are being studied, and cystatin-C is a promising marker under investigation. Finally, new strategies that could detect DN even earlier, include biomarkers such as proteomics, defining a profile of urinary protein excretion able to identify the subsequent risk of renal disease.

Proteinuria without albuminuria: urinary protein excretion by a subset of patients with burn injuries

BACKGROUND

There is disagreement regarding the utility of urinary albumin excretion as a marker for capillary injury in patients with severe burn injuries. We examined protein components in urine specimens from patients with burn injury.

METHODS

Detailed analysis was performed for a set of 5 urine specimens selected based on a high ratio of albumin-sized molecules by size-exclusion HPLC (Accumin) versus albumin by immunoassay methods. Specimens were analyzed for total protein, alpha(1)-microglobulin, alpha(1)-acid glycoprotein, cystatin C, and retinol-binding protein. Urine components were analyzed by chromatographic and electrophoretic methods. Major components were identified by mass spectrometry of tryptic peptides.

RESULTS

A subset of urine specimens had increased total protein with slight increases in albumin by immunoassay or by polyacrylamide gel electrophoresis. Albumin values by size-exclusion HPLC were more than 10-fold higher. Immunoassays for alpha(1)-microglobulin and alpha(1)-acid glycoprotein yielded concentrations 5-10 fold higher than for albumin. Other major components identified included zinc-alpha(2)-glycoprotein and leucine-rich-alpha(2)-glycoprotein.

CONCLUSIONS

A subset of patients with burn injury had increased total urinary protein resulting primarily from increased excretion of proteins such as alpha(1)-microglobulin and alpha(1)-acid glycoprotein with little increase in albumin excretion. The unusual composition of urinary proteins in these patients may relate to decreased filtered load of albumin and increased filtered load of acute phase reactants or to alterations in renal tubular protein processing. Thus, measurement of urinary albumin may have decreased sensitivity for detecting kidney injury in burn patients.

Current issues in measurement and reporting of urinary albumin excretion

BACKGROUND

Urinary excretion of albumin indicates kidney damage and is recognized as a risk factor for progression of kidney disease and cardiovascular disease. The role of urinary albumin measurements has focused attention on the clinical need for accurate and clearly reported results. The National Kidney Disease Education Program and the IFCC convened a conference to assess the current state of preanalytical, analytical, and postanalytical issues affecting urine albumin measurements and to identify areas needing improvement.

CONTENT

The chemistry of albumin in urine is incompletely understood. Current guidelines recommend the use of the albumin/creatinine ratio (ACR) as a surrogate for the error-prone collection of timed urine samples. Although ACR results are affected by patient preparation and time of day of sample collection, neither is standardized. Considerable intermethod differences have been reported for both albumin and creatinine measurement, but trueness is unknown because there are no reference measurement procedures for albumin and no reference materials for either analyte in urine. The recommended reference intervals for the ACR do not take into account the large intergroup differences in creatinine excretion (e.g., related to differences in age, sex, and ethnicity) nor the continuous increase in risk related to albumin excretion.

DISCUSSION

Clinical needs have been identified for standardization of (a) urine collection methods, (b) urine albumin and creatinine measurements based on a complete reference system, (c) reporting of test results, and (d) reference intervals for the ACR.

Comparison between immunoturbidimetry, size-exclusion chromatography, and LC-MS to quantify urinary albumin

BACKGROUND

The accurate and precise measurement of urinary albumin is critical, since even minor increases are diagnostically sensitive indicators of renal disease, cardiovascular events, and risk for death. To gain insights into potential measurement biases, we systematically compared urine albumin measurements performed by LC-MS, a clinically available immunoturbidimetric assay, and size-exclusion HPLC.

METHODS

We obtained unused clinical urine samples from 150 patients who were stratified by degrees of albuminuria (<20 mg/L, 20-250 mg/L, >250 mg/L) as determined by the immunoturbidimetric assay used in our clinical laboratory (Roche Hitachi 912). Urine albumin was then remeasured via LC-MS and HPLC (Accumin) assays.

RESULTS

The immunoturbidimetric assay, calibrated using manufacturer-supplied serum-derived calibrators (Diasorin), underestimated albumin compared with LC-MS. After calibration with purified HSA, this immunoturbidimetric assay correlated well with LC-MS. HPLC overestimated albumin compared with both LC-MS and immunoturbidimetry. The current LC-MS and HPLC assays both performed poorly at concentrations <20 mg/L.

CONCLUSIONS

Efforts are needed to establish gold-standard traceable calibrators for clinical assays. LC-MS is a specific method to quantify albumin in native urine when concentrations exceed 20 mg/L, and therefore could be employed for standardization among assays.

Effects of ramipril and rosiglitazone on cardiovascular and renal outcomes in people with impaired glucose tolerance or impaired fasting glucose: results of the Diabetes REduction Assessment with ramipril and rosiglitazone Medication (DREAM) trial

OBJECTIVE

Impaired glucose tolerance (IGT) and/or impaired fasting glucose (IFG) are risk factors for diabetes, cardiovascular disease (CVD), and kidney disease. We determined the effects of ramipril and rosiglitazone on combined and individual CVD and renal outcomes in people with IGT and/or IFG in the Diabetes REduction Assessment With ramipril and rosiglitazone Medication (DREAM) trial.

RESEARCH DESIGN AND METHODS

A total of 5,269 people aged >or=30 years, with IGT and/or IFG without known CVD or renal insufficiency, were randomized to 15 mg/day ramipril versus placebo and 8 mg/day rosiglitazone versus placebo. A composite cardiorenal outcome and its CVD and renal components were assessed during the 3-year follow-up.

RESULTS

Compared with placebo, neither ramipril (15.7% [412 of 2,623] vs. 16.0% [424 of 2,646]; hazard ratio [HR] 0.98 [95% CI 0.84-1.13]; P = 0.75) nor rosiglitazone (15.0% [394 of 2,635] vs. 16.8% [442 of 2,634]; 0.87 [0.75-1.01]; P = 0.07) reduced the risk of the cardiorenal composite outcome. Ramipril had no impact on the CVD and renal components. Rosiglitazone increased heart failure (0.53 vs. 0.08%; HR 7.04 [95% CI 1.60-31.0]; P = 0.01) but reduced the risk of the renal component (0.80 [0.68-0.93]; P = 0.005); prevention of diabetes was independently associated with prevention of the renal component (P < 0.001).

CONCLUSIONS

Ramipril did not alter the cardiorenal outcome or its components. Rosiglitazone, which reduced diabetes, also reduced the development of renal disease but not the cardiorenal outcome and increased the risk of heart failure.

Diabetic nephropathy in children and adolescents

Type 1 diabetes mellitus (T1DM) commonly occurs in childhood or adolescence, although the rising prevalence of type 2 diabetes mellitus (T2DM) in these age groups is now being seen worldwide. Diabetic nephropathy (DN) develops in 15-20% of subjects with T1DM and in similar or higher percentage of T2DM patients, causing increased morbidity and premature mortality. Although overt DN or kidney failure caused by either type of diabetes are very uncommon during childhood or adolescence, diabetic kidney disease in susceptible patients almost certainly begins soon after disease onset and may accelerate during adolescence, leading to microalbuminuria or incipient DN. Therefore, all diabetics warrant ongoing assessment of kidney function and screening for the earliest manifestations of renal injury. Pediatric health care professionals ought to understand about risk factors, strategy for prevention, method for screening, and treatment of early DN. This review considers each form of diabetes separately, including natural history, risk factors for development, screening for early manifestations, and strategy recommended for prevention and treatment of DN in children and adolescents.

Reactivity of Urinary Albumin (Microalbumin) Assays with Fragmented or Modified Albumin

Background: Controversy exists regarding occurrence and measurement of structural variants of albumin in urine. In this study, we examined cross-reactivity of in vitro modified albumins in assays for urine albumin (microalbumin).

Methods: We analyzed albumin modified by reagents, trypsin, or physical treatments or differing in primary sequence (animal albumins) with an immunoturbidimetric assay (Beckman LX20) using goat antiserum and a competitive immunoassay (Siemens Immulite) using a monoclonal antibody. We assessed occurrence of albumin fragments in urine by use of Western blotting of 24 specimens.

Results: Chemical modification, modest sequence substitution (gorilla albumin), or cleavage of albumin by cyanogen bromide (CNBr) had little effect on reactivity in the LX20 assay. Albumin extensively cleaved with trypsin retained partial reactivity. The Immulite assay generally was affected more severely by albumin modifications and sequence changes. Western blots of fresh urine specimens or specimens stored at −80 °C showed little albumin fragmentation, but some specimens stored for 3 years at −20 °C had extensively fragmented albumin that was detected by the LX20 but not the Immulite assay.

Conclusions: Nearly equivalent reactivity of intact albumin and CNBr fragments in the immunoturbidimetric assay indicates reactivity of antibodies with multiple epitopes throughout albumin. Therefore, it is difficult to abolish reactivity of albumin in this type of urine albumin assay. Differential sensitivity of 2 assays to albumin modification identifies a potential source of assay nonequivalence in measuring urinary albumin, particularly for specimens stored at −20 °C.

Measuring protein excretion in pregnancy

The recognition and detection of proteinuria has been acknowledged as an important clinical marker of renal disease since 1827 when Richard Bright published his landmark medical case reports. In more recent times, the broader community of clinicians has come to share the enthusiasm of nephrologists in recognizing the importance of protein excretion, not only as a marker of current renal disease but also as a predictor of long-term renal and cardiovascular morbidity and mortality. It is important that methods for detecting and measuring proteinuria are accurate, and this is particularly relevant to diseases that are defined by the detection of proteinuria, such as pre-eclampsia. This review will first discuss current knowledge of protein handling by the normal kidney, then the changes in normal and hypertensive pregnancy, and finally, how recent advances in our understanding of proteinuria may affect our future management of hypertensive pregnancies.

Production and Characterization of Monoclonal Antibody Against Human Serum Albumin

Hybridomas secreting monoclonal antibodies (MAbs) producing stable, specific and high affinity against human serum albumin (HSA) have been established. The aim of the present study was the production of MAbs that will be potentially used in designing immunoassay methods especially immunochromatography assay kit for screening of microalbuminuria (MAU) in the early detection of diabetic and nondiabetic nephropathy. The hybridomas were obtained by fusion of spleen cells from immunized mice with mouse myeloma cell line (SP2). After limiting dilutions three clones producing antibodies were designed as EMRC1-3, which displayed different pattern of fine specificity for HSA and low cross reaction with other proteins as elucidated by inhibition enzyme-linked immunosorbent assay (ELISA). These clones were found to be of immunoglobulin G (IgG) class with k light chain. Subclass determination showed that all three MAbs secreted IgG1 type of antibody. The results of affinity purification for the two selected clones (EMRC1 and EMRC3) displayed high affinity with no cross reactivity with any of the related protein molecules. The stable hybridomas secreting anti-HSA were expanded in 50-mL flasks for large-scale production of the required antibodies. The standard curves were constructed with a sensitivity of 10 pg per well covering up to 100 ng per well. The high binding activity to HSA antigen and having no cross reactivity with other related molecules illustrated the potential application of these antibodies as an immunodiagnostic reagent in designing an immunochromatography assay kit for screening of MAU in diabetic and nondiabetic patients.

Apparent loss of urinary albumin during long-term frozen storage: HPLC vs immunonephelometry

BACKGROUND

Urinary albumin detection by immunonephelometry is decreased by approximately 30% in samples that have been frozen at -20 degrees C. An HPLC method for assessment of urinary albumin that detects immunoreactive and immunochemically nonreactive albumin has been introduced as an alternative to immunonephelometry. We investigated whether this technique is affected by sample temperature, particularly freezing.

METHODS

Urine samples (n = 295) were collected from the general population (Prevention of Renal and Vascular End-Stage Disease Study). Samples were assessed by both immunonephelometry and HPLC when fresh and after storage at -20 degrees C for 4, 8, and 12 months and at -80 degrees C for 12 months.

RESULTS

With immunonephelometry, storage for 4, 8, and 12 months at -20 degrees C resulted in mean (SD) urine albumin changes of -21% (29%), -28% (29%), and -34% (31) (P <0.001 for trend). Storage at -80 degrees C resulted in a 5% (19%) change after 12 months of storage (not significant). With HPLC, storage for 4, 8, and 12 months at -20 degrees C resulted in urine albumin changes of -33% (28%), -43% (24%), and -55% (21%; P <0.001 vs immunonephelometry). Storage at -80 degrees C resulted in a -29% (29%) change (P <0.001 vs immunonephelometry).

CONCLUSION

Loss of albumin after freezing urine depends not only on freezing temperature but also on detection method. Detection of albumin by immunonephelometry appears to be significantly less influenced by freezing than detection by HPLC. Storage at -80 degrees C appears to prevent loss when using immunonephelometry, whereas HPLC still shows considerable loss even when urine is frozen at -80 degrees C. We propose that for reliable measurement of urine albumin, fresh samples should be used.

Albuminuria: a target for treatment of type 2 diabetic nephropathy

Both renal and cardiovascular morbidity and mortality is increased markedly in patients with type 2 diabetes. Besides the classic risk factors and markers such as glucose, blood pressure, blood lipid profile, and lifestyle (smoking, overweight), novel risk markers are identified, among them urine albumin excretion. Levels of urinary albumin excretion greater than normal are observed frequently in patients with type 2 diabetes. Moderately increased levels of albuminuria, so-called microalbuminuria, are predictive both for progressive renal function loss to diabetic nephropathy, and for cardiovascular morbidity and mortality: the higher the albuminuria level, the more chance of renal and cardiovascular complications. More advanced levels of albuminuria (overt albuminuria) are observed in patients in the diabetic nephropathy state. In this condition, renal and cardiovascular risk are extremely high, and again one may observe that the level of albumin excretion is predictive of renal and cardiovascular outcome. Several drug strategies decrease the level of urinary albumin excretion in type 2 diabetic patients. Data on using drugs that intervene in the renin-angiotensin-aldosterone-system (RAAS) are the most extensive and conclusive. RAAS intervention is a very effective strategy to decrease the amount of albumin in the urine, independent from the blood pressure decreasing characteristics of the treatment. RAAS intervention is associated with long-term renal and cardiovascular protection. Importantly, the degree of short-term albuminuria decrease is associated with the degree of renal and cardiovascular protection: the more albuminuria reduction, the more protection. The protective predictive power of the albuminuria effect of RAAS intervention is not related to (or dissociated from) the blood pressure decreasing effect of these drugs. The protective effect of RAAS intervention is present at normoalbuminuric, microalbuminuric, and overt albuminuria levels. This makes albuminuria a target for therapy in type 2 diabetes. New drug strategies that decrease or prevent albuminuria without affecting other risk factors currently are being tested, and not only will add to underscoring the need to treat albuminuria as a separate target, but also will assist in reducing the enormous residual risk burden of individual diabetic patients.

Reevaluation by High-Performance Liquid Chromatography: Clinical Significance of Microalbuminuria in Individuals at High Risk of Cardiovascular Disease in the Heart Outcomes Prevention Evaluation (HOPE) Study

BACKGROUND

In the Heart Outcomes Prevention Evaluation Study, microalbumin and albumin levels measured by using radioimmunoassay (RIA) and less than the microalbuminuria threshold in baseline urine samples were associated independently with cardiovascular (CV) events. Conventional immunoassays may underestimate albuminuria by not detecting a mildly denatured unfragmented form of albumin, immunounreactive to conventional antibodies.

METHODS

Microalbuminuria was reanalyzed in baseline samples stored at -70 degrees C for 5,358 North American participants, 1,992 with diabetes mellitus, by using a high-performance liquid chromatography (HPLC) system that also detects immunochemically nonreactive urinary albumin.

RESULTS

The HPLC compared with RIA method identified microalbuminuria in 1,585 versus 719 participants, 809 versus 423 patients with diabetes, by using a conventionally accepted albumin-creatinine ratio (ACR) of 29 mg/g or greater (>or=3 mg/mmol) as a cutoff value. HPLC-detected microalbuminuria increased risk for the primary outcome (a composite of myocardial infarction, stroke, and CV death); unadjusted hazard ratio, 1.85 (95% confidence interval, 1.57 to 2.19). Receiver operating characteristic analysis did not differentiate between HPLC- and RIA-detected microalbuminuria as predictors of CV outcomes.

CONCLUSION

The prevalence of microalbuminuria is 2 to 3 times greater with HPLC than RIA using an ACR of 29 mg/g or greater (>or=3 mg/mmol). The optimal cutoff value for detecting CV risk in the entire study population by means of RIA was 9 mg/g (0.9 mg/mmol), and with HPLC, 32 mg/g (3.4 mg/mmol). Results from this study also show different ACR cutoff values for individuals with diabetes: RIA, 13 mg/g or greater (>or=1.4 mg/mmol); HPLC, 44 mg/g or greater (>or=5.2 mg/mmol) and without diabetes: RIA, 7 mg/g or greater (>or=0.7 mg/mmol); HPLC, 29 mg/g or greater (>or=3/1 mg/mmol). Results highlight the importance of method-dependent cutoff values in the prediction of CV events.

Detection and measurement of urinary protein

PURPOSE OF REVIEW

The measurement of urine total protein and albumin is central to the diagnosis and management of subjects with kidney disease and in assessing cardiovascular risk. Accurate assessment is vital to enable detection and management of the patient with proteinuria.

RECENT FINDINGS

The spot urine protein has been suggested as an acceptable alternative to 24-h urine collections. Recent studies suggest that this holds true for screening to exclude significant proteinuria (>1 g/day) but data are lacking for the quantification of proteinuria and in assessing response to therapy. For albuminuria, while 24-h urinary albumin excretion remains the gold standard, spot urine samples are appropriate for screening. The optimal technique for the laboratory determination of urinary albumin has been questioned with the high-performance liquid chromatography-based method demonstrating significantly more albumin in the urine. Population-based studies have found dramatic increases in the prevalence of microalbuminuria with the new high-performance liquid chromatography assay. Whether this extra immunounreactive albumin detected by high-performance liquid chromatography is clinically important remains to be established.

SUMMARY

Twenty-four-hour urine collection remains the gold standard for the accurate determination of both total urinary protein and albumin. Spot urine samples can be used for screening patients for albuminuria and proteinuria. The optimal method for measuring urinary albumin concentration remains to be established.

Population prevalence of albuminuria in the Australian Diabetes, Obesity, and Lifestyle (AusDiab) study: immunonephelometry compared with high-performance liquid chromatography

BACKGROUND

Microalbuminuria is an independent risk factor for cardiovascular morbidity and mortality in the general population. Standard immunochemical urinary albumin assays detect immunoreactive albumin, whereas high-performance liquid chromatography (HPLC) detects both immunoreactive and immunounreactive albumin.

METHODS

Using data from the Australian Diabetes, Obesity, and Lifestyle cohort study of randomly selected community-based Australian adults, spot urine samples were tested for albuminuria (spot urine albumin-creatinine ratio [ACR]: normal, < 30 mg/g; microalbuminuria, 30 to 300 mg/g; and macroalbuminuria, > 300 mg/g) by using both immunonephelometry (IN) and HPLC (n = 10,010).

RESULTS

Bland-Altman analysis showed significant bias, with a greater ACR by means of HPLC, particularly at lower levels of ACR. Mean ACR was 15.8 mg/g (95% confidence interval [CI], 12.3 to 19.2) by means of IN compared with 30.0 mg/g (95% CI, 27.0 to 35.0) by means of HPLC. The prevalence of microalbuminuria was 4 times greater by means of HPLC compared with IN (20% versus 5.5%). In all demographic and comorbid subgroups associated with microalbuminuria, the prevalence of microalbuminuria increased by 2 to 4 times. A total of 1,743 subjects (17.4%) classified as normoalbuminuric by means of IN were reclassified as microalbuminuric by means of HPLC. Using multivariate logistic regression, women, patients with untreated and treated hypertension, and those with impaired glucose tolerance or diabetes were associated significantly with a change in category from normoalbuminuric to microalbuminuria by means of HPLC.

CONCLUSION

HPLC measures significantly more urinary albumin within the normoalbuminuria and microalbuminuria range, resulting in a significant increase in prevalence of microalbuminuria. Longitudinal studies are needed to determine whether the extra individuals identified by means of HPLC are at increased risk for developing hard clinical outcomes (renal and cardiovascular).

The analysis and characterisation of immuno-unreactive urinary albumin in healthy volunteers

OBJECTIVES

To compare the analysis of different forms of intact albumin in urine from healthy volunteers. To determine contamination by common non-albumin proteins on HPLC analysis of urinary albumin and of purified immuno-unreactive albumin.

DESIGN AND METHODS

Overnight urine samples collected from healthy volunteers were analysed for total albumin (immunoreactive plus immuno-unreactive) by HPLC and densitometry following native PAGE separation and for immunoreactive albumin by RIA. The contamination by non-albumin proteins of the HPLC analysis of urinary albumin and of immuno-unreactive albumin preparations was determined by ELISA. Immuno-unreactive albumin was tested for Co2+-binding capacity.

RESULTS AND CONCLUSIONS

HPLC analysis of healthy urine generates higher ACR values than immunological methods due to the presence of immuno-unreactive albumin. Immuno-unreactive albumin cannot be accounted for by the non-albumin urinary proteins tested. Isolated immuno-unreactive albumin is not recognised by antibodies to common urinary proteins or by an array of anti-albumin antibodies and behaves like serum albumin in terms of HPLC elution, native PAGE migration, and cobalt ion binding.

Coelution of other proteins with albumin during size-exclusion HPLC: Implications for analysis of urinary albumin

BACKGROUND

Size-exclusion HPLC has been used as an alternative to immunoassays for quantifying urinary albumin (microalbumin). Systematically higher values for the HPLC method have been proposed to result from nonimmunoreactive albumin.

METHODS

We evaluated separation of purified proteins and urinary components by size-exclusion HPLC using a Zorbax Bio Series GF-250 column eluted with phosphate-buffered saline. Urinary components eluting in the "albumin" peak were analyzed by mass spectrometry and reversed-phase HPLC.

RESULTS

Several proteins, such as transferrin, alpha1-proteinase inhibitor, alpha1-acid glycoprotein, and alpha2-HS glycoprotein, analyzed as purified components, were not resolved from albumin by size-exclusion HPLC. Peaks for other proteins, such as IgG and urinary components identified as dimers of alpha1-microglobulin and immunoglobulin light chains, overlapped with the albumin peak. Profiles of urine specimens showed variable amounts of components overlapping with albumin. Furthermore, the albumin peak obtained by size-exclusion HPLC was found by mass spectrometry and reversed-phase HPLC to contain multiple components in addition to albumin.

CONCLUSIONS

Size-exclusion HPLC does not resolve albumin from several other proteins in urine. The albumin peak resolved by this technique, although predominantly composed of albumin, contains several coeluting globulins that would contribute to overestimation of albumin concentration by size-exclusion HPLC.