Biological Variation of Plasma and Urinary Markers of Acute Kidney Injury in Patients with Chronic Kidney Disease.

BACKGROUND: Identification of acute kidney injury (AKI) is predominantly based on changes in plasma creatinine concentration, an insensitive marker. Alternative biomarkers have been proposed. The reference change value (RCV), the point at which biomarker change can be inferred to have occurred with statistical certainty, provides an objective assessment of change in serial tests results in an individual. METHODS: In 80 patients with chronic kidney disease, weekly measurements of blood and urinary biomarker concentrations were undertaken over 6 weeks. Variability was determined and compared before and after adjustment for urinary creatinine and across subgroups stratified by level of kidney function, proteinuria, and presence or absence of diabetes. RESULTS: RCVs were determined for whole blood, plasma, and urinary neutrophil gelatinase-associated lipocalin (111%, 59%, and 693%, respectively), plasma cystatin C (14%), creatinine (17%), and urinary kidney injury molecule 1 (497%), tissue inhibitor of metalloproteinases 2 (454%), N-acetyl-ß-d-glucosaminidase (361%), interleukin-18 (819%), albumin (430%), and α1-microglobulin (216%). Blood biomarkers exhibited lower variability than urinary biomarkers. Generally, adjusting urinary biomarker concentrations for creatinine reduced (P < 0.05) within-subject biological variability (CVI). For some markers, variation differed (P < 0.05) between subgroups. CONCLUSIONS: These data can form a basis for application of these tests in clinical practice and research studies and are applicable across different levels of kidney function and proteinuria and in the presence or absence of diabetes. Most of the studied biomarkers have relatively high CVI (noise) but also have reported large concentration changes in response to renal insult (signal); thus progressive change should be detectable (high signal-to-noise ratio) when baseline data are available.

Do acute elevations of serum creatinine in primary care engender an increased mortality risk?

BACKGROUND: The significant impact Acute Kidney Injury (AKI) has on patient morbidity and mortality emphasizes the need for early recognition and effective treatment. AKI presenting to or occurring during hospitalisation has been widely studied but little is known about the incidence and outcomes of patients experiencing acute elevations in serum creatinine in the primary care setting where people are not subsequently admitted to hospital. The aim of this study was to define this incidence and explore its impact on mortality. METHODS: The study cohort was identified by using hospital data bases over a six month period. INCLUSION CRITERIA: People with a serum creatinine request during the study period, 18 or over and not on renal replacement therapy.The patients were stratified by a rise in serum creatinine corresponding to the Acute Kidney Injury Network (AKIN) criteria for comparison purposes. Descriptive and survival data were then analysed.Ethical approval was granted from National Research Ethics Service (NRES) Committee South East Coast and from the National Information Governance Board. RESULTS: The total study population was 61,432. 57,300 subjects with 'no AKI', mean age 64.The number (mean age) of acute serum creatinine rises overall were, 'AKI 1' 3,798 (72), 'AKI 2' 232 (73), and 'AKI 3' 102 (68) which equates to an overall incidence of 14,192 pmp/year (adult). Unadjusted 30 day survival was 99.9% in subjects with 'no AKI', compared to 98.6%, 90.1% and 82.3% in those with 'AKI 1', 'AKI 2' and 'AKI 3' respectively. After multivariable analysis adjusting for age, gender, baseline kidney function and co-morbidity the odds ratio of 30 day mortality was 5.3 (95% CI 3.6, 7.7), 36.8 (95% CI 21.6, 62.7) and 123 (95% CI 64.8, 235) respectively, compared to those without acute serum creatinine rises as defined. CONCLUSIONS: People who develop acute elevations of serum creatinine in primary care without being admitted to hospital have significantly worse outcomes than those with stable kidney function.

What is the real impact of acute kidney injury?

BACKGROUND: Acute kidney injury (AKI) is a common clinical problem. Studies have documented the incidence of AKI in a variety of populations but to date we do not believe the real incidence of AKI has been accurately documented in a district general hospital setting.The aim here was to describe the detected incidence of AKI in a typical general hospital setting in an unselected population, and describe associated short and long-term outcomes. METHODS: A retrospective observational database study from secondary care in East Kent (adult catchment population of 582,300). All adult patients (18 years or over) admitted between 1st February 2009 and 31st July 2009, were included. Patients receiving chronic renal replacement therapy (RRT), maternity and day case admissions were excluded. AKI was defined by the acute kidney injury network (AKIN) criteria. A time dependent risk analysis with logistic regression and Cox regression was used for the analysis of in-hospital mortality and survival. RESULTS: The incidence of AKI in the 6 month period was 15,325 pmp/yr (adults) (69% AKIN1, 18% AKIN2 and 13% AKIN3). In-hospital mortality, length of stay and ITU utilisation all increased with severity of AKI. Patients with AKI had an increase in care on discharge and an increase in hospital readmission within 30 days. CONCLUSIONS: This data comes closer to the real incidence and outcomes of AKI managed in-hospital than any study published in the literature to date. Fifteen percent of all admissions sustained an episode of AKI with increased subsequent short and long term morbidity and mortality, even in those with AKIN1. This confers an increased burden and cost to the healthcare economy, which can now be quantified. These results will furnish a baseline for quality improvement projects aimed at early identification, improved management, and where possible prevention, of AKI.

Isometric Exercise Training and Arterial Hypertension: An Updated Review.

Hypertension is recognised as a leading attributable risk factor for cardiovascular disease and premature mortality. Global initiatives towards the prevention and treatment of arterial hypertension are centred around non-pharmacological lifestyle modification. Exercise recommendations differ between professional and scientific organisations, but are generally unanimous on the primary role of traditional aerobic and dynamic resistance exercise. In recent years, isometric exercise training (IET) has emerged as an effective novel exercise intervention with consistent evidence of reductions in blood pressure (BP) superior to that reported from traditional guideline-recommended exercise modes. Despite a wealth of emerging new data and endorsement by select governing bodies, IET remains underutilised and is not widely prescribed in clinical practice. This expert-informed review critically examines the role of IET as a potential adjuvant tool in the future clinical management of BP. We explore the efficacy, prescription protocols, evidence quality and certainty, acute cardiovascular stimulus, and physiological mechanisms underpinning its anti-hypertensive effects. We end the review with take-home suggestions regarding the direction of future IET research.

Change in the estimated glomerular filtration rate over time and risk of all-cause mortality.

Using a community-based cohort we studied the association between changes in the estimated glomerular filtration rate (eGFR) over time and the risk of all-cause mortality. We identified 529,312 adults who had at least three outpatient eGFR measurements over a 4-year period from a provincial laboratory repository in Alberta, Canada. Two indices of change in eGFR were evaluated: the absolute annual rate of change (in ml/min per 1.73 m(2) per year) and the annual percentage change (percent/year). The adjusted mortality risk associated with each category of change in eGFR was assessed, using stable eGFR (no change) as the reference. Over a median follow-up of 2.5 years there were 32,372 deaths. Compared to the reference participants, those with the greatest absolute annual decline less than or equal to 5 ml/min per 1.73 m(2) per year had significantly increased mortality (hazard ratio of 1.52) adjusted for covariates and kidney function at baseline (last eGFR measurement). Participants with the greatest increase in eGFR of 5 ml/min per 1.73 m(2) per year or more also had significantly increased mortality (adjusted hazard ratio of 2.20). A similar pattern was found when change in eGFR was quantified as an annual percentage change. Thus, both declining and increasing eGFR were independently associated with mortality and underscore the importance of identifying change in eGFR over time to improve mortality risk prediction.

Accuracy of the MDRD (Modification of Diet in Renal Disease) study and CKD-EPI (CKD Epidemiology Collaboration) equations for estimation of GFR in the elderly.

BACKGROUND: Glomerular filtration rate (GFR) is a measure of kidney function, commonly estimated using equations that adjust serum creatinine concentration for age, race, and sex. The Modification of Diet in Renal Disease (MDRD) Study equation is widely used, but underestimates GFR at higher levels. The serum creatinine-based Chronic Kidney Disease-Epidemiology Collaboration (CKD-EPI(cr)) equation generally provides more accurate estimation at GFR >60 mL/min/1.73 m(2). Newer equations have been reported using cystatin C concentration either alone (CKD-EPI(cys)) or in combination with creatinine concentration (CKD-EPI(cr-cys)). None of these equations has been well validated in older people. We tested the accuracy of these equations in people 74 years or older compared with GFR measured by a reference method. STUDY DESIGN: Diagnostic test evaluation in a prospective cohort. SETTING & PARTICIPANTS: Participants (n = 394; median age, 80 [range, 74-97] years) recruited from nephrology clinics and the community. INDEX TEST: GFR estimated using the MDRD Study, CKD-EPI(cr), CKD-EPI(cys) and CKD-EPI(cr-cys) equations. REFERENCE TEST: GFR measured using an iohexol clearance method. RESULTS: Median measured GFR was 53.4 (range, 7.2-100.9) mL/min/1.73 m(2). MDRD Study-, CKD-EPI(cr)-, and CKD-EPI(cr-cys)-estimated GFRs overestimated GFR (median differences of 3.5 [P< 0.001], 1.7 [P < 0.001], and 0.8 [P = 0.02] mL/min/1.73 m(2), respectively); the CKD-EPI(cys) equation was unbiased. Accuracy (percentage of estimates within 30% of measured GFR [P(30)]) was 81%, 83%, 86%, and 86% for the MDRD Study, CKD-EPI(cr), CKD-EPI(cys), and CKD-EPI(cr-cys) equations, respectively. Accuracy of the MDRD Study equation was inferior (P = 0.004) to the CKD-EPI(cr) equation at GFR >60 mL/min/1.73 m(2). LIMITATIONS: Those of non-European ancestry were not included. For practical reasons, only a 4-hour sampling protocol was used for iohexol clearance. CONCLUSIONS: The CKD-EPI(cr) equation appeared less biased and was more accurate than the MDRD Study equation. No equation achieved an ideal P(30) in the overall population. Our data suggest that GFR estimation is as satisfactory in older people of European ancestry as it has been reported to be in younger individuals.

Invasive Gastrointestinal Mucormycosis.

Invasive mucormycosis is an opportunistic fungal infection that can be devastating in immunosuppressed patients. Gastrointestinal infection is rare, but carries among the highest mortality rates of its major clinical presentations. We present a case of invasive gastrointestinal mucormycosis in a patient who underwent recent chemotherapy and autologous stem cell transplant. Initial histopathology revealed cytomegalovirus infection, which was treated before subsequent diagnosis of mucormycosis on repeat bowel biopsy. Our case highlights a myriad of risk factors that increase the potential for serious infection by this pervasive fungus.

Predicting lifespan-extending chemical compounds for C. elegans with machine learning and biologically interpretable features.

Recently, there has been a growing interest in the development of pharmacological interventions targeting ageing, as well as in the use of machine learning for analysing ageing-related data. In this work, we use machine learning methods to analyse data from DrugAge, a database of chemical compounds (including drugs) modulating lifespan in model organisms. To this end, we created four types of datasets for predicting whether or not a compound extends the lifespan of C. elegans (the most frequent model organism in DrugAge), using four different types of predictive biological features, based on: compound-protein interactions, interactions between compounds and proteins encoded by ageing-related genes, and two types of terms annotated for proteins targeted by the compounds, namely Gene Ontology (GO) terms and physiology terms from the WormBase's Phenotype Ontology. To analyse these datasets, we used a combination of feature selection methods in a data pre-processing phase and the well-established random forest algorithm for learning predictive models from the selected features. In addition, we interpreted the most important features in the two best models in light of the biology of ageing. One noteworthy feature was the GO term "Glutathione metabolic process", which plays an important role in cellular redox homeostasis and detoxification. We also predicted the most promising novel compounds for extending lifespan from a list of previously unlabelled compounds. These include nitroprusside, which is used as an antihypertensive medication. Overall, our work opens avenues for future work in employing machine learning to predict novel life-extending compounds.

Clinical Characteristics and Outcomes of Drug-Induced Acute Kidney Injury Cases.

Introduction: Drug-induced acute kidney injury (DI-AKI) is a frequent adverse event. The identification of DI-AKI is challenged by competing etiologies, clinical heterogeneity among patients, and a lack of accurate diagnostic tools. Our research aims to describe the clinical characteristics and predictive variables of DI-AKI. Methods: We analyzed data from the Drug-Induced Renal Injury Consortium (DIRECT) study (NCT02159209), an international, multicenter, observational cohort study of enriched clinically adjudicated DI-AKI cases. Cases met the primary inclusion criteria if the patient was exposed to at least 1 nephrotoxic drug for a minimum of 24 hours prior to AKI onset. Cases were clinically adjudicated, and inter-rater reliability (IRR) was measured using Krippendorff's alpha. Variables associated with DI-AKI were identified using L1 regularized multivariable logistic regression. Model performance was assessed using the area under the receiver operating characteristic curve (ROC AUC). Results: A total of 314 AKI cases met the eligibility criteria for this analysis, and 271 (86%) cases were adjudicated as DI-AKI. The majority of the AKI cases were recruited from the United States (68%). The most frequent causal nephrotoxic drugs were vancomycin (48.7%), nonsteroidal antiinflammatory drugs (18.2%), and piperacillin/tazobactam (17.8%). The IRR for DI-AKI adjudication was 0.309. The multivariable model identified age, vascular capacity, hyperglycemia, infections, pyuria, serum creatinine (SCr) trends, and contrast media as significant predictors of DI-AKI with good performance (ROC AUC 0.86). Conclusion: The identification of DI-AKI is challenging even with comprehensive adjudication by experienced nephrologists. Our analysis identified key clinical characteristics and outcomes of DI-AKI compared to other AKI etiologies.

One-year change in kidney function is associated with an increased mortality risk.

BACKGROUND: Serum creatinine is routinely measured to estimate glomerular filtration rate (GFR). Long-term cohort studies report that death is a likelier outcome than progression to kidney failure. However, it is unclear how short-term changes in estimated GFR (eGFR) over a 1-year period relate to subsequent mortality risk. METHODS: Using a provincial laboratory registry from Alberta, Canada, we identified 598,397 adults who had ≥2 outpatient eGFR measurements at least 6 months apart during a 1-year accrual period. Change in kidney function was categorized by both changes in eGFR category and percent change ≥25% into 5 groups: certain drop, uncertain drop, stable (no change in CKD category), uncertain rise, and certain rise. Cox proportional hazards models, adjusting for baseline covariates, kidney function, and proteinuria were used to estimate the risk of all-cause mortality associated with each group change in kidney function in reference to stable kidney function. RESULTS: Among the study participants, 447,570 (74.8%) had stable kidney function, 19,591 (3.3%) had a certain drop, and 22,171 (3.7%) had a certain rise in kidney function. Participants with change in kidney function (both drop and rise) were older, more likely to be female, and had a higher prevalence of comorbidities in comparison to those with stable kidney function. There were 51,473 (8.6%) deaths during a median follow-up of 3.5 years. Compared to participants with stable kidney function, those with a certain drop had an almost twofold increased mortality risk (hazard ratio 1.89, 95% CI 1.83-1.95) adjusted for baseline eGFR, proteinuria, and covariates. Participants with a certain rise (3.7%) in kidney function also experienced an increased mortality risk (hazard ratio 1.51, 95% CI 1.46-1.56) compared to those with stable kidney function. Risk of death was similarly increased with adjustment for eGFR at the last visit. CONCLUSION: Change in kidney function of ≥25% in any direction over a 1-year period is associated with a substantially increased risk of mortality.

Engaging primary care in CKD initiatives: the UK experience.

Over the last decade, since the introduction of an international classification of chronic kidney disease (CKD) and the development of simple tools to detect people with CKD, primary care has had to adapt to a new paradigm of disease. Significantly, improved identification of CKD, and increased awareness and understanding of the potential associated adverse outcomes, has in turn required the development, implementation and integration of new policies, models and pathways of care. The UK health care system, including primary care, is uniquely positioned to respond to new initiatives. Despite early reservations, CKD has gone from an unheard of condition in primary care prior to 2006 to one where people with this condition are recorded in disease registers and increasingly managed in accordance with evidence-based guidance. National and local initiatives implemented together have contributed to the improved understanding and management of CKD in primary care in the UK and are showing signs of having made significant health gains in CKD.

Short-term change in kidney function and risk of end-stage renal disease.

BACKGROUND: It is unclear what degree of change in the eGFR over a 1-year period indicates clinically significant progression, and whether this change adds additional information beyond that obtained by a single eGFR measure alone. METHODS: We included 598 397 adults who had at least two outpatient eGFR measurements (at least 6 months apart) during 1-year accrual period in Alberta, Canada. Change in kidney function (using the first and last eGFR) was defined by change in kidney function category with confirmation based on percent (%) change in eGFR [(last eGFR - first eGFR)/first eGFR × 100]. The groups for change in kidney function were thus defined as: 'certain drop' (drop in CKD category with ≥25% decrease in the eGFR); 'uncertain drop' (drop in CKD category with <25% decrease in the eGFR); 'stable' (no change in CKD category); 'uncertain rise' (rise in CKD category with <25% rise in the eGFR) and 'certain rise' (rise in CKD category with ≥25% increase in the eGFR). Adjusted end-stage renal disease (ESRD) rates (per 1000 person-years) for each group of change in kidney function were calculated using Poisson regression. Adjusted risks of ESRD associated with change in kidney function, in reference to stable kidney function, were estimated. RESULTS: Among the 598 397 participants, 74.8% (n = 447 570) had stable (no change in CKD category), 3.3% (n = 19 591) had a certain drop and 3.7% (n = 22 171) had a certain rise in kidney function. Participants who experienced a certain change in kidney function (both drop and rise) were older, more likely to be female, and had a higher prevalence of comorbidities, in comparison with those with stable kidney function. There were 1966 (0.3%) ESRD events over a median follow-up of 3.5 years. Compared with participants with stable kidney function, after adjustment for covariates, and the first eGFR measurement, those with certain drop had 5-fold increased risk of ESRD (HR: 5.11; 95% CI: 4.56-5.71), whereas those with an uncertain drop had 2-fold increased risk (HR: 2.13; 95% CI: 1.84-2.47). After adjustment for the eGFR and covariates at the last visit, neither a certain nor uncertain drop in the eGFR was associated with an increased ESRD risk. The ESRD risk associated with the last eGFR level, adjusted for the slope over time, were 2.89 (95% CI: 2.35-3.55), 10.98 (95% CI: 8.69-13.87), 35.20 (95% CI: 27.95-44.32) and 147.96 (116.92-187.23) for categories 2, 3a, 3b and 4, respectively, in reference to category 1. CONCLUSIONS: A change in eGFR category accompanied by ≥25% decline (certain drop) is associated with increased ESRD risk. However, this elevated risk is captured by patient characteristics and eGFR at the last visit, suggesting that eGFR trajectories based on more than two serum creatinine measurements over a period longer than 1 year are required to determine ESRD risk and allow more reliable risk prediction.

The primary care physician: nephrology interface for the identification and treatment of chronic kidney disease.

This article explores ways in which early identification of chronic kidney disease (CKD) and promotion of the concept of CKD as a modifiable risk can be achieved through transcending traditional primary and secondary care boundaries. National and regional strategies aimed at early identification of CKD in the community are reviewed, together with those aimed at implementation of management to reduce the risk both of progression of CKD and of complications.

Influence of donor C3 allotype on late renal-transplantation outcome.

BACKGROUND: The complement system has a critical role in both the innate and the adaptive immune responses. In humans, C3 exists as two main allotypes, F (fast) and S (slow), which are known to affect the incidence of inflammatory disease. We conducted a study to address the influence of these alleles on late renal-graft outcome. METHODS: We determined the C3 allotypes of 662 pairs of adult kidney donors and recipients from 1993 through 2002 and then related C3F/S polymorphism status to demographic and clinical outcome data. The median length of follow-up was 3.3 years. RESULTS: Analysis of 513 pairs of white donors and recipients identified 113 C3S/S recipients of a C3S/F or a C3F/F kidney and 179 C3S/S recipients of a C3S/S kidney. Graft survival was significantly better with a C3F/F or C3F/S donor allotype than a C3S/S allotype (P=0.05). The hazard ratio for graft loss of C3S/S kidneys, as compared with C3F/F or C3F/S kidneys, was 2.21 (95 percent confidence interval, 1.04 to 4.72; P=0.04). The graft function of C3F/F or C3F/S donor kidneys was significantly better than that of C3S/S donor kidneys (P<0.001). The effect of the C3F allele was specific to recipients who did not themselves possess this allele. Multivariate analysis excluded effects of other factors known to influence graft outcome. CONCLUSIONS: Expression of C3 alleles by donor renal cells appears to have a differential effect on late graft outcome. Among white C3S/S recipients, receipt of a C3F/F or C3F/S donor kidney, rather than a C3S/S donor kidney, is associated with a significantly better long-term outcome. These findings suggest that the two alleles have functional differences.

Referral patterns to renal services: what has changed in the past 4 years?

BACKGROUND: Awareness of chronic kidney disease (CKD) has been prompted by the publication of several large epidemiological studies since 2002. This has led to various initiatives for the early identification and management of CKD, including the introduction of automated glomerular filtration rate (GFR) reporting and renal indicators in the primary care quality and outcomes framework (QOF) since April 2006. These initiatives were intended to promote identification of CKD and have had an impact on referral patterns to renal services. The aim of this study was to understand the nature of this impact in a catchment population of 1.2 million people. METHODS: Data were collected and recorded from all written referrals from primary care between 1 April 2004 and 31 March 2008. Referral patterns for each postcode sector were mapped using Microsoft MapPoint 2004. The effect of chance on referral patterns was modelled by using small area analysis techniques. The association between the CKD prevalence reported from QOF data and the estimated CKD prevalence was examined at post-code district level. RESULTS: There were 1461 referrals in 2 years prior to the introduction of the initiatives and 2890 referrals in the 2 years post-introduction. The main reason for referral in both groups was impaired renal function or previously established renal disease. Reported comorbidity was similar between the groups. Mapping showed that there was wide heterogeneity in referral behaviour in the first 2 years of the study, which was less in the second period. Small area analysis suggested that the variation that led to the extremal quotients observed in both of the study periods was not due to random variation in referral pattern alone. There was no correlation between the reported CKD prevalence and the referral rates. CONCLUSION: Referral patterns have changed between 1 April 2004 and 31 March 2008. The main findings were an increase in referral rate and in the age at referral without a significant change in reported comorbidity of the people referred. The main increase in referral rates was seen in more advanced CKD suggesting more targeted referral of patients with CKD to renal services.

Taking services to the streets over the party season.

Christmas and New Year festivities notoriously result in increased attendance at emergency departments (EDs). The knock-on effect of this in Solihull, in the West Midlands, is that, when ambulance staff and police accompany patients to hospital, the locality is temporarily under-resourced by these services. To address this problem, a collaborative project was implemented to enable advanced clinical practitioners, with consultant support, to assess, treat and potentially discharge patients from a specially constructed emergency facility situated in Solihull town centre. This has reduced the number of ED admissions and transfers, and resulted in significant cost and time savings for the ambulance service.

Symmetric dimethylarginine is a stronger predictor of mortality risk than asymmetric dimethylarginine among older people with kidney disease.

BACKGROUND: Circulating asymmetric dimethylarginine and symmetric dimethylarginine are increased in patients with kidney disease. Symmetric dimethylarginine is considered a good marker of glomerular filtration rate, while asymmetric dimethylarginine is a marker of cardiovascular risk. However, a link between symmetric dimethylarginine and all-cause mortality has been reported. In the present study, we evaluated both dimethylarginines as risk and glomerular filtration rate markers in a cohort of elderly white individuals, both with and without chronic kidney disease. METHODS: Glomerular filtration rate was measured in 394 individuals aged >74 years using an iohexol clearance method. Plasma asymmetric dimethylarginine, symmetric dimethylarginine and iohexol were measured simultaneously using isotope dilution tandem mass spectrometry. RESULTS: Plasma asymmetric dimethylarginine concentrations were increased ( P < 0.01) in people with glomerular filtration rate <60 mL/min/1.73 m2 compared with those with glomerular filtration rate ≥60 mL/min/1.73 m2, but did not differ ( P > 0.05) between those with glomerular filtration rate 30-59 mL/min/1.73 m2 and <30 mL/min/1.73 m2. Plasma symmetric dimethylarginine increased consistently across declining glomerular filtration rate categories ( P < 0.0001). Glomerular filtration rate had an independent effect on plasma asymmetric dimethylarginine concentration, while glomerular filtration rate, gender, body mass index and haemoglobin had independent effects on plasma symmetric dimethylarginine concentration. Participants were followed up for a median of 33 months. There were 65 deaths. High plasma asymmetric dimethylarginine ( P = 0.0412) and symmetric dimethylarginine ( P < 0.0001) concentrations were independently associated with reduced survival. CONCLUSIONS: Among elderly white individuals with a range of kidney function, symmetric dimethylarginine was a better marker of glomerular filtration rate and a stronger predictor of outcome than asymmetric dimethylarginine. Future studies should further evaluate the role of symmetric dimethylarginine as a marker of outcome and assess its potential value as a marker of glomerular filtration rate.

Development of a multivariable gene-expression signature targeting T-cell-mediated rejection in peripheral blood of kidney transplant recipients validated in cross-sectional and longitudinal samples.

BACKGROUND: Acute T-cell mediated rejection (TCMR) is usually indicated by alteration in serum-creatinine measurements when considerable transplant damage has already occurred. There is, therefore, a need for non-invasive early detection of immune signals that would precede the onset of rejection, prior to transplant damage. METHODS: We examined the RT-qPCR expression of 22 literature-based genes in peripheral blood samples from 248 patients in the Kidney Allograft Immune Biomarkers of Rejection Episodes (KALIBRE) study. To account for post-transplantation changes unrelated to rejection, we generated time-adjusted gene-expression residuals from linear mixed-effects models in stable patients. To select genes, we used penalised logistic regression based on 27 stable patients and 27 rejectors with biopsy-proven T-cell-mediated rejection, fulfilling strict inclusion/exclusion criteria. We validated this signature in i) an independent group of stable patients and patients with concomitant T-cell and antibody-mediated-rejection, ii) patients from an independent study, iii) cross-sectional pre-biopsy samples from non-rejectors and iv) longitudinal follow-up samples covering the first post-transplant year from rejectors, non-rejectors and stable patients. FINDINGS: A parsimonious TCMR-signature (IFNG, IP-10, ITGA4, MARCH8, RORc, SEMA7A, WDR40A) showed cross-validated area-under-ROC curve 0.84 (0.77-0.88) (median, 2.5th-97.5th centile of fifty cross-validation cycles), sensitivity 0.67 (0.59-0.74) and specificity 0.85 (0.75-0.89). The estimated probability of TCMR increased seven weeks prior to the diagnostic biopsy and decreased after treatment. Gene expression in all patients showed pronounced variability, with up to 24% of the longitudinal samples in stable patients being TCMR-signature positive. In patients with borderline changes, up to 40% of pre-biopsy samples were TCMR-signature positive. INTERPRETATION: Molecular marker alterations in blood emerge well ahead of the time of clinically overt TCMR. Monitoring a TCMR-signature in peripheral blood could unravel T-cell-related pro-inflammatory activity and hidden immunological processes. This additional information could support clinical management decisions in cases of patients with stable but poor kidney function or with inconclusive biopsy results.