HPLC-detected albuminuria predicts mortality

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.

Electrochemical immunosensor utilizing electrodeposited Au nanocrystals and dielectrophoretically trapped PS/Ag/ab-HSA nanoprobes for detection of microalbuminuria at point of care

In this study, we have fabricated a simple disposable electrochemical immunosensor for the point of care testing of microalbuminuria, a well-known clinical biomarker for the onset of chronic kidney disease. The immunosensor is fabricated by screen-printing carbon interdigitated microelectrodes on a flexible plastic substrate and utilizes electrochemical impedance spectroscopy to enable direct and label free immunosensing by analyzing interfacial changes on the electrode surface. To improve conductivity and biocompatibility of the screen-printed electrodes, we have modified it with gold nanoparticles, which are electrodeposited using linear sweep voltammetry. To enable efficient immobilization of HSA antibodies, we have developed novel PS/Ag/ab-HSA nanoprobes (polystyrene nanoparticle core with silver nanoshells covalently conjugated to HSA antibodies), and these nanoprobes are trapped on the electrode surface using dielectrophoresis. Each immunosensor has two sensing sites corresponding to test and control to improve specificity by performing differential analysis. Immunosensing results show that the normalized impedance response is linearly dependent on albumin concentration in the clinically relevant range with good repeatability. We have also developed a portable impedance readout module that can analyze the data obtained from the immunosensor and transmit it wirelessly for cloud computing. Consequently, the developed immunosensing platform can be extended to the detection of a range of immunoreactions and shows promise for point of diagnosis and public healthcare monitoring.

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.

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.

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.

Adiponectin, total antioxidant status, and urine albumin excretion in the low-risk "Golden Years" type 1 diabetes mellitus cohort

Adiponectin is associated with inflammation and oxidative stress. Levels are reduced in type 2 diabetes mellitus and coronary heart disease. Conversely, levels are elevated in type 1 diabetes mellitus (T1DM) and associated with microalbuminuria and diabetic nephropathy. An explanation may be that elevated adiponectin in T1DM represents a beneficial counterregulatory response to disease. Our aim was to examine adiponectin in relation to urinary albumin excretion and plasma total antioxidant status (TAOS) in subjects with long-standing T1DM. Serum adiponectin and plasma TAOS were measured in 338 samples from the Golden Years cohort. These subjects have T1DM for at least 50 years and are at low risk of complications. Subjects were divided into normoalbuminuria, microalbuminuria, and macroalbuminuria groups. Adiponectin was elevated in women (20.53 ± 5.94 vs 11.8 ± 3.6 mg/L, P < .001); therefore, the samples were sex stratified. Within men, adiponectin was higher in those with macroalbuminuria (normoalbuminuria vs microalbuminuria vs macroalbuminuria: 10.97 ± 3.26 vs 11.55 ± 3.50 vs 23.63 ± 7.07 mg/L, P = .002). In women, no difference was observed (20.48 ± 5.61 vs 20.75 ± 7.04 vs 29.62 ± 7.81 mg/L, respectively; P = .42). Plasma TAOS did not differ by groups. The correlation between adiponectin and TAOS showed a linear increase from normoalbuminuria, microalbuminuria, to macroalbuminuria in men (r = 0.33, P = .001; r = 0.48, P < .001; r = 0.59, P = .04) and women (r = 0.25, P = .01; r = 0.63, P < .001; r = 0.79, P = .08). Adiponectin was higher in women. Within men, levels were significantly higher in the presence of macroalbuminuria. In both sexes, adiponectin and TAOS were correlated, which was most marked with micro-/macroalbuminuria. The increase in adiponectin in the face of an insult may be a compensatory mechanism to reduce oxidative burden.

Review: Serum and urine biomarkers of kidney disease: A pathophysiological perspective

The use of reliable biomarkers is becoming increasingly important for the improved management of patients with acute and chronic kidney diseases. Recent developments have identified a number of novel biomarkers in serum or urine that can determine the potential risk of kidney damage, distinguish different types of renal injury, predict the progression of disease and have the potential to assess the efficacy of therapeutic intervention. Some of these biomarkers can be used independently while others are more beneficial when used in combination with knowledge of other clinical risk factors. Advances in gene expression analysis, chromatography, mass spectrometry and the development of sensitive enzyme-linked immunosorbent assays have facilitated accurate quantification of many biomarkers. This review primarily focuses on describing new and established biomarkers, which identify and measure the various pathophysiological processes that promote kidney disease. It provides an overview of some of the different classes of renal biomarkers that can be assessed in serum/plasma and urine, including markers of renal function, oxidative stress, structural and cellular injury, immune responses and fibrosis. However, it does not explore the current status of these biomarkers in terms of their clinical validation.

Clinical application of a novel sliver nanoparticles biosensor based on localized surface plasmon resonance for detecting the microalbuminuria

In order to explore the clinical application of the nanobiosensor based on localized surface plasmon resonance (LSPR), we used our LSPR biosensor to detect the microalbuminuria in this work. The sliver nanoparticles were fabricated by using nanosphere lithography. The anti-human albumin antibody was immobilized on the sensor surface by amine coupling method. The different concentrations of commercial albumin and albumin in urine samples from three mild preeclampsia patients were determined according to the peak of LSPR extinction spectra. Under optimum conditions, our results showed that the biosensor displayed a detection limit of 1 ng/ml and wide dynamic range of 1 ng/ml to 1 μg/ml. Furthermore, the microalbuminuria of three patients was determined by our biosensor within a short assay time, without sample purification. This biosensor proposed herein is easy to prepare and could be used for low-cost, rapid, label-free, and sensitive screening of the microalbuminuria. This approach provides a promising platform for developing clinical diagnostic applications.

Serum and Urinary Biomarkers Determination and Their Significance in Diagnosis of Kidney Diseases

Chronic kidney disease (CKD) is becoming a major public health problem worldwide due to the epidemic increase of patients on renal replacement therapy and their high cardiovascular morbidity and mortality. The only effective approach to this problem is prevention and early detection of CKD. In addition, despite significant improvements in therapeutics, the mortality and morbidity associated with acute kidney injury (AKI) remain high. A major reason for this is the lack of early markers for AKI, and hence an unacceptable delay in initiating therapy. Therefore, there is a pressing need to develop biomarkers (proteins and other molecules in the blood or urine) for renal disease, which might assist in diagnosis and prognosis and might provide endpoints for clinical trials of drugs designed to slow the progression of renal insufficiency. Besides serum creatinine, promising novel biomarkers for AKI include a plasma panel (neutrophil gelatinase-associated lipocalin-NGAL and cystatin C) and a urine panel (NGAL, kidney injury molecule-1, interleukin-18, cystatin C, alpha 1-microglobulin, Fetuin-A, Gro-alpha, and meprin). For CKD, these include a similar plasma panel and a urine panel (NGAL, asymmetric dimethylarginine, and liver-type fatty acid-binding protein). Increased plasma and urinary TGF-β1 levels might contribute to the development of chronic tubulointerstitial disease, indicating the possible therapeutic implications. Furthermore, to differentiate lower urinary tract infection and pyelonephritis interleukin-6 and serum procalcitonin levels were introduced. It will be important in future studies to validate the sensitivity and specificity of these biomarker panels in clinical samples from large cohorts and in multiple clinical situations.

Chronic kidney disease in Tasmania

AIM

Chronic kidney disease (CKD) is a progressive disease which is becoming a major public health issue due to its high rate of premature death, poor quality of life and expensive end-stage treatment (dialysis or transplantation). The burden of this chronic condition in a community setting was examined.

METHODS

Data were obtained from 369,098 Tasmanian adults (aged >or=18 years) and included 1,640,687 measurements of creatinine taken between 1995 and 2007. In 2007 alone, testing comprised 25.5% of the state's adult population. A modelled estimate of CKD prevalence was developed.

RESULTS

For those at risk of CKD (aged >50 years), 50.6%, 70.2% and 82% had a measured creatinine (and reported estimated glomerular filtration rate (eGFR)) during the last 1, 2 and 3 years respectively. However, only 9.4% of people with eGFR of less than 60 mL/min per 1.73 m(2) had albuminuria formally measured. Estimated prevalence of stage III or greater CKD (eGFR <60 mL/min per 1.73 m(2)) was at least 11.4% of women and 8.6% of men during 2007. Detection of low eGFR increased significantly over the last 13 years. There was a large geographic variation throughout Tasmania and high relative mortality with lower eGFR. There is a broad gap between the number of people with eGFR of less than 15 mL/min per 1.73 m(2) (stage V CKD) and those receiving dialysis treatment.

CONCLUSION

The number of people identified with low eGFR has increased significantly since 1995 with a large geographic variation. Despite this, testing for kidney disease (by measuring serum creatinine and albuminuria) in people at risk is still suboptimal.

How should proteinuria be detected and measured?

Proteinuria is a classic sign of kidney disease and its presence carries powerful prognostic information. Although proteinuria testing is enshrined in clinical practice guidelines, there is surprising variation among such guidelines as to the definition of clinically significant proteinuria. There is also poor agreement as to whether proteinuria should be defined in terms of albumin or total protein loss, with a different approach being used to stratify diabetic and non-diabetic nephropathy. Further, the role of reagent strip devices in the detection and assessment of proteinuria is unclear. This review explores these issues in relation to recent national and international guidelines on chronic kidney disease (CKD) and epidemiological evidence linking proteinuria and clinical outcome. The authors argue that use of urinary albumin measurement as the front-line test for proteinuria detection offers the best chance of improving the sensitivity, quality and consistency of approach to the early detection and management of CKD.

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.