Plasma Kidney Injury Molecule 1 in CKD: Findings From the Boston Kidney Biopsy Cohort and CRIC Studies.

RATIONALE & OBJECTIVE: Plasma kidney injury molecule 1 (KIM-1) is a sensitive marker of proximal tubule injury, but its association with risks of adverse clinical outcomes across a spectrum of kidney diseases is unknown. STUDY DESIGN: Prospective, observational cohort study. SETTING & PARTICIPANTS: 524 individuals enrolled into the Boston Kidney Biopsy Cohort (BKBC) Study undergoing clinically indicated native kidney biopsy with biopsy specimens adjudicated for semiquantitative scores of histopathology by 2 kidney pathologists and 3,800 individuals with common forms of chronic kidney disease (CKD) enrolled into the Chronic Renal Insufficiency Cohort (CRIC) Study. EXPOSURE: Histopathologic lesions and clinicopathologic diagnosis in cross-sectional analyses, baseline plasma KIM-1 levels in prospective analyses. OUTCOMES: Baseline plasma KIM-1 levels in cross-sectional analyses, kidney failure (defined as initiation of kidney replacement therapy) and death in prospective analyses. ANALYTICAL APPROACH: Multivariable-adjusted linear regression models tested associations of plasma KIM-1 levels with histopathologic lesions and clinicopathologic diagnoses. Cox proportional hazards models tested associations of plasma KIM-1 levels with future kidney failure and death. RESULTS: In the BKBC Study, higher plasma KIM-1 levels were associated with more severe acute tubular injury, tubulointerstitial inflammation, and more severe mesangial expansion after multivariable adjustment. Participants with diabetic nephropathy, glomerulopathies, and tubulointerstitial disease had significantly higher plasma KIM-1 levels after multivariable adjustment. In the BKBC Study, CKD in 124 participants progressed to kidney failure and 85 participants died during a median follow-up time of 5 years. In the CRIC Study, CKD in 1,153 participants progressed to kidney failure and 1,356 participants died during a median follow-up time of 11.5 years. In both cohorts, each doubling of plasma KIM-1 level was associated with an increased risk of kidney failure after multivariable adjustment (hazard ratios of 1.19 [95% CI, 1.03-1.38] and 1.10 [95% CI, 1.06-1.15] for BKBC and CRIC, respectively). There was no statistically significant association of plasma KIM-1 levels with death in either cohort. LIMITATIONS: Generalizability and unmeasured confounding. CONCLUSIONS: Plasma KIM-1 is associated with underlying tubulointerstitial and mesangial lesions and progression to kidney failure in 2 cohort studies of individuals with kidney diseases.

Biological Variability of Estimated GFR and Albuminuria in CKD.

RATIONALE & OBJECTIVE: Determining whether a change in estimated glomerular filtration rate (eGFR) or albuminuria is clinically significant requires knowledge of short-term within-person variability of the measurements, which few studies have addressed in the setting of chronic kidney disease. STUDY DESIGN: Cross-sectional study with multiple collections over less than 4 weeks. SETTING & PARTICIPANTS: Clinically stable outpatients with chronic kidney disease (N=50; mean age, 56.8 years; median eGFR, 40mL/min/1.73m2; median urinary albumin-creatinine ratio (UACR), 173mg/g). EXPOSURE: Repeat measurements from serially collected samples across 3 study visits. OUTCOMES: Measurements of urine albumin concentration (UAC), UACR, and plasma creatinine, cystatin C, ß2-microglobulin (B2M), and beta trace protein (BTP). ANALYTICAL APPROACH: We calculated within-person coefficients of variation (CVw) values and corresponding reference change positive and negative (RCVpos and RCVneg) values using log-transformed measurements. RESULTS: Median CVw (RCVpos; RCVneg) values of filtration markers were 5.4% (+16%; -14%) for serum creatinine, 4.1% (+12%; -11%) for cystatin C, 7.4% (+23%; -18%) for BTP, and 5.6% (+17%; -14%) for B2M. Results for albuminuria were 33.2% (+145%; -59%) for first-morning UAC, 50.6% (+276%; -73%) for random spot UAC, 32.5% (+141%; -58%) for first-morning UACR, and 29.7% (124%; -55%) for random spot UACR. CVw values for filtration markers were comparable across the range of baseline eGFRs. CVw values for UAC and UACR were comparable across the range of baseline albuminuria values. LIMITATIONS: Small sample size limits the ability to detect differences in variability across markers. Participants were recruited and followed up in a clinical and not research setting, so some preanalytical factors could not be controlled. CONCLUSIONS: eGFR markers appear to have relatively low short-term within-person variability, whereas variability in albuminuria appears to be high, making it difficult to distinguish random variability from meaningful biologic changes.

Urine biomarkers of tubular injury do not improve on the clinical model predicting chronic kidney disease progression.

Few investigations have evaluated the incremental usefulness of tubular injury biomarkers for improved prediction of chronic kidney disease (CKD) progression. As such, we measured urinary kidney injury molecule-1, neutrophil gelatinase-associated lipocalin, N-acetyl-ß-D-glucosaminidase and liver fatty acid binding protein under highly standardized conditions among 2466 enrollees of the prospective Chronic Renal Insufficiency Cohort Study. During 9433 person-years of follow-up, there were 581 cases of CKD progression defined as incident end-stage renal disease or halving of the estimated glomerular filtration rate. Levels of the urine injury biomarkers, normalized for urine creatinine, were strongly associated with CKD progression in unadjusted Cox proportional hazard models with hazard ratios in the range of 7 to 15 comparing the highest with the lowest quintiles. However, after controlling for the serum creatinine-based estimated glomerular filtration rate and urinary albumin/creatinine ratio, none of the normalized biomarkers was independently associated with CKD progression. None of the biomarkers improved on the high (0.89) C-statistic for the base clinical model. Thus, among patients with CKD, risk prediction with a clinical model that includes the serum creatinine-based estimated glomerular filtration rate and the urinary albumin/creatinine ratio is not improved on with the addition of renal tubular injury biomarkers.

Relationship of proximal tubular injury to chronic kidney disease as assessed by urinary kidney injury molecule-1 in five cohort studies.

BACKGROUND: The primary biomarkers used to define CKD are serum creatinine and albuminuria. These biomarkers have directed focus on the filtration and barrier functions of the kidney glomerulus even though albuminuria results from tubule dysfunction as well. Given that proximal tubules make up ∼90% of kidney cortical mass, we evaluated whether a sensitive and specific marker of proximal tubule injury, urinary kidney injury molecule-1 (KIM-1), is elevated in individuals with CKD or with risk factors for CKD. METHODS: We measured urinary KIM-1 in participants of five cohort studies from the USA and Sweden. Participants had a wide range of kidney function and were racially and ethnically diverse. Multivariable linear regression models were used to test the association of urinary KIM-1 with demographic, clinical and laboratory values. RESULTS: In pooled, multivariable-adjusted analyses, log-transformed, creatinine-normalized urinary KIM-1 levels were higher in those with lower eGFR {ß = -0.03 per 10 mL/min/1.73 m(2) [95% confidence interval (CI) -0.05 to -0.02]} and greater albuminuria [ß = 0.16 per unit of log albumin:creatinine ratio (95% CI 0.15-0.17)]. Urinary KIM-1 levels were higher in current smokers, lower in blacks than nonblacks and lower in users versus nonusers of angiotensin-converting enzyme inhibitors and angiotensin receptor blockers. CONCLUSION: Proximal tubule injury appears to be an integral and measurable element of multiple stages of CKD.

Association of urinary KIM-1, L-FABP, NAG and NGAL with incident end-stage renal disease and mortality in American Indians with type 2 diabetes mellitus.

AIMS/HYPOTHESIS: Kidney injury molecule 1 (KIM-1), liver fatty acid-binding protein (L-FABP), N-acetyl-ß-D-glucosaminidase (NAG) and neutrophil gelatinase-associated lipocalin (NGAL) are urinary biomarkers of renal tubular injury. We examined their association with incident end-stage renal disease (ESRD) and all-cause mortality in American Indians with type 2 diabetes. METHODS: Biomarker concentrations were measured in baseline urine samples in 260 Pima Indians who were followed for a median of 14 years. HRs were reported per SD of creatinine (Cr)-normalised log-transformed KIM-1, NAG and NGAL, and for three categories of L-FABP. RESULTS: During follow-up, 74 participants developed ESRD and 101 died. Median concentrations of KIM-1/Cr, NAG/Cr and NGAL/Cr and the proportion of detectable L-FABP were highest in those with macroalbuminuria (p < 0.001 for KIM-1/Cr, NAG/Cr and L-FABP; p = 0.006 for NGAL/Cr). After multivariable adjustment, NGAL/Cr was positively associated with ESRD (HR 1.59, 95% CI 1.20, 2.11) and mortality (HR 1.39, 95% CI 1.06, 1.82); L-FABP/Cr was inversely associated with ESRD (HR [for highest vs lowest tertile] 0.40, 95% CI 0.19, 0.83). Addition of NGAL/Cr to models that included albuminuria and glomerular filtration rate increased the c-statistic for predicting ESRD from 0.828 to 0.833 (p = 0.001) and for death from 0.710 to 0.722 (p = 0.018). Addition of L-FABP/Cr increased the c-statistic for ESRD from 0.828 to 0.832 (p = 0.042). CONCLUSIONS/INTERPRETATION: In Pima Indians with type 2 diabetes, urinary concentrations of NGAL and L-FABP are associated with important health outcomes, but they are unlikely to add to risk prediction with standard markers in a clinically meaningful way given the small increase in the c-statistic.

Urinary monocyte chemoattractant protein-1 and hepcidin and early diabetic nephropathy lesions in type 1 diabetes mellitus.

BACKGROUND: Urinary monocyte chemoattractant protein-1 (MCP-1) and hepcidin are potential biomarkers of renal inflammation. We examined their association with development of diabetic nephropathy (DN) lesions in normotensive normoalbuminuric subjects with type 1 diabetes (T1D) from the Renin-Angiotensin System Study. METHODS: Biomarker concentrations were measured in baseline urine samples from 224 subjects who underwent kidney biopsies at baseline and after 5 years. Fifty-eight urine samples below the limit of quantitation (LOQ, 28.8 pg/mL) of the MCP-1 assay were assigned concentrations of LOQ/√2 for analysis. Relationships between ln(MCP-1/Cr) or ln(hepcidin/Cr) and morphometric variables were assessed by sex using multiple linear regression after adjustment for age, T1D duration, HbA1c, mean arterial pressure, albumin excretion rate (AER) and glomerular filtration rate (GFR). In models that examined changes in morphometric variables, the baseline morphometric value was also included. RESULTS: Baseline mean age was 24.6 years, mean duration of T1D 11.2 years, median AER 6.4 µg/min and mean iohexol GFR 129 mL/min/1.73 m(2). No associations were found between hepcidin/Cr and morphometric variables. Higher MCP-1/Cr was associated with higher interstitial fractional volume at baseline and after 5 years in women (baseline partial r = 0.244, P = 0.024; 5-year partial r = 0.299, P = 0.005), but not in men (baseline partial r = -0.049, P = 0.678; 5-year partial r = 0.026, P = 0.830). MCP-1 was not associated with glomerular lesions in either sex. CONCLUSIONS: Elevated urinary MCP-1 concentration measured before clinical findings of DN in women with T1D was associated with changes in kidney interstitial volume, suggesting that inflammatory processes may be involved in the pathogenesis of early interstitial changes in DN.

Urinary Biomarkers and Risk of ESRD in the Atherosclerosis Risk in Communities Study.

BACKGROUND AND OBJECTIVES: Liver fatty acid binding protein (L-FABP), kidney injury molecule 1 (KIM-1), N-acetyl-ß-d-glucosaminidase (NAG), and neutrophil gelatinase-associated lipocalin (NGAL) are urinary markers of tubular injury that may also be markers of chronic kidney damage. We evaluated the association of these markers with incident ESRD in a community-based sample from the Atherosclerosis Risk in Communities Study. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: This was a matched case-control study of 135 patients with ESRD and 186 controls who were matched on sex, race, kidney function, and diabetes status at baseline (Atherosclerosis Risk in Communities Study visit 4, 1996-1998). Urinary KIM-1 indexed to creatinine (Cr), NAG/Cr, NGAL/Cr, and L-FABP/Cr were measured in stored spot urine samples from the baseline examination. Associations of KIM-1/Cr, NAG/Cr, and NGAL/Cr with patients with incident ESRD through 2008 were modeled continuously and categorically (quartiles) using conditional logistic regression. L-FABP/Cr was modeled only categorically because of a large number of measurements below the lower limit of detection for the assay (2.4 ng/ml). RESULTS: No significant associations were observed for NAG/Cr, NGAL/Cr, or L-FABP/Cr with ESRD. Those in the highest category for KIM-1/Cr had a higher risk of ESRD compared with those with undetectable biomarker levels (reference group) in unadjusted models (odds ratio, 2.24; 95% confidence interval, 1.97 to 4.69; P=0.03) or adjustment for age (odds ratio, 2.23; 95% confidence interval, 1.06 to 4.67; P=0.03). This association was attenuated with additional adjustment for baseline kidney function (odds ratio, 2.02; 95% confidence interval, 0.95 to 4.31; P=0.07 after additional adjustment for eGFR and natural log of the urinary albumin-to-creatinine ratio). No association between KIM-1/Cr and ESRD was found when KIM-1/Cr was analyzed as a continuous variable. CONCLUSIONS: Elevated urinary KIM-1/Cr may be associated with a higher risk of incident ESRD, but it does not add to risk prediction after accounting for traditional markers of kidney function in this population.

Cross-Disciplinary Biomarkers Research: Lessons Learned by the CKD Biomarkers Consortium.

Significant advances are needed to improve the diagnosis, prognosis, and management of persons with CKD. Discovery of new biomarkers and improvements in currently available biomarkers for CKD hold great promise to achieve these necessary advances. Interest in identification and evaluation of biomarkers for CKD has increased substantially over the past decade. In 2009, the National Institute of Diabetes and Digestive and Kidney Diseases established the CKD Biomarkers Consortium (http://www.ckdbiomarkersconsortium.org/), a multidisciplinary, collaborative study group located at over a dozen academic medical centers. The main objective of the consortium was to evaluate new biomarkers for purposes related to CKD in established prospective cohorts, including those enriched for CKD. During the first 5 years of the consortium, many insights into collaborative biomarker research were gained that may be useful to other investigators involved in biomarkers research. These lessons learned are outlined in this Special Feature and include a wide range of issues related to biospecimen collection, storage, and retrieval, and the internal and external quality assessment of laboratories that performed the assays. The authors propose that investigations involving biomarker discovery and validation are greatly enhanced by establishing and following explicit quality control metrics, including the use of blind replicate and proficiency samples, by carefully considering the conditions under which specimens are collected, handled, and stored, and by conducting pilot and feasibility studies when there are concerns about the condition of the specimens or the accuracy or reproducibility of the assays.

Setting up a PCR laboratory.

INTRODUCTIONDevelopment of the polymerase chain reaction (PCR) as a basic component of the molecular biology laboratory has occurred very rapidly from its inception in 1985. As PCR became more widely used, scientists rapidly learned more about it and, as a result, learned that PCR had its strong points and its deficiencies. Very quickly, PCR demonstrated its power to amplify very small amounts (e.g., a single copy) of template nucleic acid and to amplify different nucleic acids (e.g., DNA and RNA). At the same time, laboratory personnel learned that this biochemical reaction had a unique deficiency, namely, a strong susceptibility to contamination from its own product. This article is devoted to establishing a PCR laboratory whose operations will give reliable and contamination-free results.

Evaluation of an automated preanalytical robotic workstation at two academic health centers.

BACKGROUND: Purchase of automated systems in today's clinical laboratory needs justification based on demonstrable improvements in efficiency and a sound payback model. Few studies provide information on laboratory automation that focuses on the preanalytical portion of specimen processing. METHODS: We recently evaluated an automated preanalytical processing unit (GENESIS FE500) at two academic health centers. This preanalytical unit processes blood specimens through automated specimen sorting, centrifugation, decapping, labeling, aliquoting, and placement of the processed specimen in the analytical rack. We quantified the output of the FE500 by processing >3000 barcode-labeled specimens according to a protocol designed to test all of the features of this automated specimen-processing unit. RESULTS: Depending on the batch size, aliquot number requested, and percentage of tubes that required centrifugation, the mean system output performance varied between 93 and 502 total tubes/h. Throughput increased when the batch size expanded from 40 or 100 samples (mean = 211 total tubes processed/h) to batch sizes of 200 and 300 tubes (mean = 474 total tube processed/h). The GENESIS FE500 processed specimen tubes differing in size from 13 x 65 mm (width x height) to 16 x 100. At one site, the FE500 was operated by one person, compared with the three individuals required to perform the same tasks manually. Finally, the specimen-processing error rate determined at one of the institutions was significantly reduced. CONCLUSIONS: We conclude that the GENESIS FE500 effectively reduces the labor associated with specimen processing; decreases the number of laboratory errors that occur with specimen sorting, labeling, and aliquoting; and improves the integrity of specimen handling throughout the steps of specimen processing.

Genotyping of essential hypertension single-nucleotide polymorphisms by a homogeneous PCR method with universal energy transfer primers.

BACKGROUND: Human hypertension is a complex, multifactorial disease with a heritability of more than 30-50%. A genetic screening test based on analysis of multiple single-nucleotide polymorphisms (SNPs) to assess the likelihood of developing hypertension would be helpful for disease management. METHODS: Tailed allele-specific primers were designed to amplify by PCR six biallelic SNP loci [three in G protein-coupled receptor kinase type 4 (GRK4): R65L, A142V, and A486V; two in angiotensinogen: -6G-->A and M235T; and one in aldosterone synthase: -344C-->T] associated with essential hypertension. PCRs of SNP loci were coupled (via a common sequence of 21 nucleotide tails) to incorporate Universal Amplifluor(TM) primers labeled with fluorescein or sulforhodamine in a homogeneous format. Use of Amplifluors in SNP PCRs produced labeled amplicons, the fluorescence of which was quantified by a microplate reader and then analyzed via an Excel macro to provide genotypes for all six SNP loci. Unique restriction endonucleases were identified for five SNP loci that could independently confirm homogeneous PCR results when needed. RESULTS: We developed six homogeneous PCR assays that were set up, performed, and fluorometrically analyzed in 96-well microplates. Allele frequencies were determined for six SNPs in 60 Italian hypertensive patients and a control group of 60 normotensive persons. A significant correlation (P = 0.034) between one SNP [GRK4 (A486V)] and the hypertensive patients was observed. Genotyping results for five of six SNPs were confirmed by digesting corresponding amplicons with locus-specific restriction endonucleases. CONCLUSIONS: We developed a simple and homogeneous fluorescent protocol that has been used to determine the SNP genotype for six loci in a population of hypertensive and normotensive persons. We also observed a significant association (P = 0.034) between one SNP (A486V) and an Italian population of mildly hypertensive patients.