Sodium MRI: a new frontier in imaging in nephrology

PURPOSE OF REVIEW

This review focuses on the recent technological advances in quantitative sodium (Na) MRI to provide a noninvasive measure of tissue viability for use in clinical studies of patients with kidney disease. Na MRI is the only noninvasive imaging technique that allows for the absolute spatial quantification of tissue sodium concentration (TSC), providing assessment of the corticomedullary sodium gradient (CMSG) in the kidney, and allowing measures of TSC in the skin and muscle.

RECENT FINDINGS

Na MRI of the kidney has demonstrated the sensitivity to measure the CMSG, providing the normal range in healthy individuals and demonstrating a reduction in CMSG in kidney disease and transplanted kidneys. Studies using Na and H MRI have shown that in humans, skeletal muscle and skin can store sodium without water retention, and that sodium concentrations in muscle and skin increase with advancing age. Recent studies have shown that TSC can be mobilised during haemodialysis, and that skin sodium content links closely to left ventricular mass in patients with chronic kidney disease.

SUMMARY

Na MRI is currently a research technique, but with future advances, Na MRI has potential to become a noninvasive renal biomarker and a measure of tissue sodium storage for clinical studies.

The clinical utility and cost impact of cystatin C measurement in the diagnosis and management of chronic kidney disease: A primary care cohort study

BACKGROUND

To reduce over-diagnosis of chronic kidney disease (CKD) resulting from the inaccuracy of creatinine-based estimates of glomerular filtration rate (GFR), UK and international guidelines recommend that cystatin-C-based estimates of GFR be used to confirm or exclude the diagnosis in people with GFR 45-59 ml/min/1.73 m2 and no albuminuria (CKD G3aA1). Whilst there is good evidence for cystatin C being a marker of GFR and risk in people with CKD, its use to define CKD in this manner has not been evaluated in primary care, the setting in which most people with GFR in this range are managed.

METHODS AND FINDINGS

A total of 1,741 people with CKD G3a or G3b defined by 2 estimated GFR (eGFR) values more than 90 days apart were recruited to the Renal Risk in Derby study between June 2008 and March 2010. Using Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations, we compared GFR estimated from creatinine (eGFRcreat), cystatin C (eGFRcys), and both (eGFRcreat-cys) at baseline and over 5 years of follow-up. We analysed the proportion of participants with CKD G3aA1 reclassified to 'no CKD' or more advanced CKD with the latter two equations. We further assessed the impact of using cystatin-C-based eGFR in risk prediction equations for CKD progression and all-cause mortality and investigated non-GFR determinants of eGFRcys. Finally, we estimated the cost implications of implementing National Institute for Health and Care Excellence (NICE) guidance to use eGFRcys to confirm the diagnosis in people classified as CKD G3aA1 by eGFRcreat. Mean eGFRcys was significantly lower than mean eGFRcreat (45.1 ml/min/1.73 m2, 95% CI 44.4 to 45.9, versus 53.6 ml/min/1.73 m2, 95% CI 53.0 to 54.1, P < 0.001). eGFRcys reclassified 7.7% (50 of 653) of those with CKD G3aA1 by eGFRcreat to eGFR ≥ 60 ml/min/1.73 m2. However, a much greater proportion (59.0%, 385 of 653) were classified to an eGFR category indicating more severe CKD. A similar pattern was seen using eGFRcreat-cys, but lower proportions were reclassified. Change in eGFRcreat and eGFRcys over 5 years were weakly correlated (r = 0.33, P < 0.001), but eGFRcys identified more people as having CKD progression (18.2% versus 10.5%). Multivariable analysis using eGFRcreat as an independent variable identified age, smoking status, body mass index, haemoglobin, serum uric acid, serum albumin, albuminuria, and C reactive protein as non-GFR determinants of eGFRcys. Use of eGFRcys or eGFRcreat-cys did not improve discrimination in risk prediction models for CKD progression and all-cause mortality compared to similar models with eGFRcreat. Application of the NICE guidance, which assumed cost savings, to participants with CKD G3aA1 increased the cost of monitoring by £23 per patient, which if extrapolated to be applied throughout England would increase the cost of testing and monitoring CKD by approximately £31 million per year. Limitations of this study include the lack of a measured GFR and the potential lack of ethnic diversity in the study cohort.

CONCLUSIONS

Implementation of current guidelines on eGFRcys testing in our study population of older people in primary care resulted in only a small reduction in diagnosed CKD but classified a greater proportion as having more advanced CKD than eGFRcreat. Use of eGFRcys did not improve risk prediction in this population and was associated with increased cost. Our data therefore do not support implementation of these recommendations in primary care. Further studies are warranted to define the most appropriate clinical application of eGFRcys and eGFRcreat-cys.

Associations of fibroblast growth factor 23, vitamin D and parathyroid hormone with 5-year outcomes in a prospective primary care cohort of people with chronic kidney disease stage 3

OBJECTIVES

Vitamin D deficiency, elevated fibroblast growth factor 23 (FGF23) and elevated parathyroid hormone (PTH) have each been associated with increased mortality in people with chronic kidney disease (CKD). Previous studies have focused on the effects of FGF23 in relatively advanced CKD. This study aims to assess whether FGF23 is similarly a risk factor in people with early CKD, and how this risk compares to that associated with vitamin D deficiency or elevated PTH.

DESIGN

Prospective cohort study.

SETTING

Thirty-two primary care practices.

PARTICIPANTS

One thousand six hundred and sixty-four people who met Kidney Disease: Improving Global Outcomes (KDIGO) definitions for CKD stage 3 (two measurements of estimated glomerular filtration rate (eGFR) between 30 and 60 mL/min/1.73 m² at least 90 days apart) prior to study recruitment.

OUTCOME MEASURES

All-cause mortality over the period of study follow-up and progression of CKD defined as a 25% fall in eGFR and a drop in GFR category, or an increase in albuminuria category.

RESULTS

Two hundred and eighty-nine participants died during the follow-up period. Vitamin D deficiency (HR 1.62, 95% CI 1.01 to 2.58) and elevated PTH (HR 1.42, 95% CI 1.09 to 1.84) were independently associated with all-cause mortality. FGF23 was associated with all-cause mortality in univariable but not multivariable analysis. Fully adjusted multivariable models of CKD progression showed no association with FGF23, vitamin D status or PTH.

CONCLUSIONS

In this cohort of predominantly older people with CKD stage 3 and low risk of progression, vitamin D deficiency and elevated PTH were independent risk factors for all-cause mortality but elevated FGF23 was not. While FGF23 may have a role as a risk marker in high-risk populations managed in secondary care, our data suggest that it may not be as important in CKD stage 3, managed in primary care.

TRIAL REGISTRATION NUMBER

National Institute for Health Research Clinical Research Portfolio Study Number 6632.

Patients' Experiences After CKD Diagnosis: A Meta-ethnographic Study and Systematic Review

BACKGROUND

Chronic kidney disease (CKD) is often asymptomatic at first diagnosis, and awareness of CKD is low in the general population. Thus, individuals who are unexpectedly identified as having CKD may struggle to adjust to living with this diagnosis. This study aims to synthesize qualitative research exploring patients' views and experiences of a CKD diagnosis and how they adjust to it.

STUDY DESIGN

Systematic review and meta-ethnography.

SETTING & POPULATION

Adult patients with CKD stages 1 to 5.

SEARCH STRATEGY & SOURCES

MEDLINE, PsycINFO, CINAHL, Embase, and Web of Science were searched from the earliest date available to November 2015. Qualitative studies were selected that explored patients' views and experiences of a CKD diagnosis and their adjustment.

ANALYTICAL APPROACH

Meta-ethnography was adopted to synthesize the findings.

RESULTS

10 studies involving 596 patients with CKD from secondary-care settings were included. 7 key themes were identified: a challenging diagnosis, diverse beliefs about causation, anticipated concerns about progression, delaying disease progression, unmet informational needs, psychosocial impact of CKD, and adjustment to life with CKD.

LIMITATIONS

Limited to views and experiences of participants in included studies, which were mostly conducted in high-income countries. Studies not written in English were excluded. Transferability of findings to other populations may be limited.

CONCLUSIONS

This review highlights variation in patients' understanding of CKD, an overall lack of information on the trajectory of CKD, and a need for psychosocial support, especially in later stages, to help patients adjust to living with CKD. Future research that acknowledges CKD as a condition with diverse complicating morbidities and explores how patients' information and psychosocial needs vary according to severity and comorbid conditions would be beneficial. This will support delivery of easily understandable, timely, and targeted information about CKD, as well as practical advice about recommended lifestyle changes.

Chronic kidney disease: towards a risk-based approach

Chronic kidney disease (CKD) affects 8-16% of adults worldwide and is associated with multiple adverse outcomes. It includes a heterogeneous group of conditions with widely varied associated risks; risk stratification is therefore vital for clinical management. Use of the CKD Epidemiology Collaboration (CKD-EPI) equation to estimate glomerular filtration rate (GFR) instead of the Modification of Diet in Renal Disease (MDRD) equation will reduce, though not eliminate, over-diagnosis of CKD. Cystatin C is recommended as an alternative measure of GFR but is not yet widely used. A new classification system for CKD, which includes GFR and albuminuria, has been endorsed by the National Institute for Health and Care Excellence to aid risk stratification and a recently validated formula, requiring only age, gender, eGFR and albuminuria, is useful to predict risk of end-stage kidney disease (ESKD). A risk-based approach will facilitate appropriate treatment for people at high risk of developing ESKD while sparing the majority, who are at low risk, from unnecessary intervention.

Chronic kidney disease: towards a risk-based approach

Chronic kidney disease (CKD) affects 8-16% of adults worldwide and is associated with multiple adverse outcomes. It includes a heterogeneous group of conditions with widely varied associated risks; risk stratification is therefore vital for clinical management. Use of the CKD Epidemiology Collaboration (CKD-EPI) equation to estimate glomerular filtration rate (GFR) instead of the Modification of Diet in Renal Disease (MDRD) equation will reduce, though not eliminate, over-diagnosis of CKD. Cystatin C is recommended as an alternative measure of GFR but is not yet widely used. A new classification system for CKD, which includes GFR and albuminuria, has been endorsed by the National Institute for Health and Care Excellence to aid risk stratification and a recently validated formula, requiring only age, gender, eGFR and albuminuria, is useful to predict risk of end-stage kidney disease (ESKD). A risk-based approach will facilitate appropriate treatment for people at high risk of developing ESKD while sparing the majority, who are at low risk, from unnecessary intervention.

Intradialytic Cardiac Magnetic Resonance Imaging to Assess Cardiovascular Responses in a Short-Term Trial of Hemodiafiltration and Hemodialysis

Hemodynamic stress during hemodialysis (HD) results in recurrent segmental ischemic injury (myocardial stunning) that drives cumulative cardiac damage. We performed a fully comprehensive study of the cardiovascular effect of dialysis sessions using intradialytic cardiac magnetic resonance imaging (MRI) to examine the comparative acute effects of standard HD versus hemodiafiltration (HDF) in stable patients. We randomly allocated 12 patients on HD (ages 32-72 years old) to either HD or HDF. Patients were stabilized on a modality for 2 weeks before undergoing serial cardiac MRI assessment during dialysis. Patients then crossed over to the other modality and were rescanned after 2 weeks. Cardiac MRI measurements included cardiac index, stroke volume index, global and regional contractile function (myocardial strain), coronary artery flow, and myocardial perfusion. Patients had mean±SEM ultrafiltration rates of 3.8±2.9 ml/kg per hour during HD and 4.4±2.5 ml/kg per hour during HDF (P=0.29), and both modalities provided a similar degree of cooling. All measures of systolic contractile function fell during HD and HDF, with partial recovery after dialysis. All patients experienced some degree of segmental left ventricular dysfunction, with severity proportional to ultrafiltration rate and BP reduction. Myocardial perfusion decreased significantly during HD and HDF. Treatment modality did not influence any of the cardiovascular responses to dialysis. In conclusion, in this randomized, crossover study, there was no significant difference in the cardiovascular response to HDF or HD with cooled dialysate as assessed with intradialytic MRI.

Regional Variation in Acute Kidney Injury Requiring Dialysis in the English National Health Service from 2000 to 2015 - A National Epidemiological Study

Background

The absence of effective interventions in presence of increasing national incidence and case-fatality in acute kidney injury requiring dialysis (AKI-D) warrants a study of regional variation to explore any potential for improvement. We therefore studied regional variation in the epidemiology of AKI-D in English National Health Service over a period of 15 years.

Method

We analysed Hospital Episode Statistics data for all patients with a diagnosis of AKI-D, using ICD-10-CM codes, in English regions between 2000 and 2015 to study temporal changes in regional incidence and case-fatality.

Results

Of 203,758,879 completed discharges between 1^st April 2000 and 31^st March 2015, we identified 54,252 patients who had AKI-D in the nine regions of England. The population incidence of AKI-D increased variably in all regions over 15 years; however, the regional variation decreased from 3·3-fold to 1·3-fold (p<0·01). In a multivariable adjusted model, using London as the reference, in the period of 2000–2005, the North East (odd ratio (OR) 1·38; 95%CI 1·01, 1·90), East Midlands (OR 1·38; 95%CI 1·01, 1·90) and West Midlands (OR 1·38; 95%CI 1·01, 1·90) had higher odds for death, while East of England had lower odds for death (OR 0·66; 95% CI 0·49, 0·90). The North East had higher OR in all three five-year periods as compared to the other eight regions. Adjusted case-fatality showed significant variability with temporary improvement in some regions but overall there was no significant improvement in any region over 15 years.

Conclusions

We observed considerable regional variation in the epidemiology of AKI-D that was not entirely attributable to variations in demographic or other identifiable clinical factors. These observations make a compelling case for further research to elucidate the reasons and identify interventions to reduce the incidence and case-fatality in all regions.

Chronic Kidney Disease in Primary Care: Outcomes after Five Years in a Prospective Cohort Study

BACKGROUND

Chronic kidney disease (CKD) is commonly managed in primary care, but most guidelines have a secondary care perspective emphasizing the risk of end-stage kidney disease (ESKD) and need for renal replacement therapy. In this prospective cohort study, we sought to study in detail the natural history of CKD in primary care to better inform the appropriate emphasis for future guidance.

METHODS AND FINDINGS

In this study, 1,741 people with CKD stage 3 were individually recruited from 32 primary care practices in Derbyshire, United Kingdom. Study visits were undertaken at baseline, year 1, and year 5. Binomial logistic regression and Cox proportional hazards models were used to model progression, CKD remission, and all-cause mortality. We used Kidney Disease: Improving Global Outcomes (KDIGO) criteria to define CKD progression and defined CKD remission as the absence of diagnostic criteria (estimated glomerular filtration rate [eGFR] >60 ml/min/1.73 m2 and urine albumin-to-creatinine ratio [uACR] <3 mg/mmol) at any study visit. Participants were predominantly elderly (mean ± standard deviation (SD) age 72.9 ± 9.0 y), with relatively mild reduction in GFR (mean ± SD eGFR 53.5 ± 11.8 mL/min/1,73 m2) and a low prevalence of albuminuria (16.9%). After 5 y, 247 participants (14.2%) had died, most of cardiovascular causes. Only 4 (0.2%) developed ESKD, but 308 (17.7%) evidenced CKD progression by KDIGO criteria. Stable CKD was observed in 593 participants (34.1%), and 336 (19.3%) met the criteria for remission. Remission at baseline and year 1 was associated with a high likelihood of remission at year 5 (odds ratio [OR] = 23.6, 95% CI 16.5-33.9 relative to participants with no remission at baseline and year 1 study visits). Multivariable analyses confirmed eGFR and albuminuria as key risk factors for predicting adverse as well as positive outcomes. Limitations of this study include reliance on GFR estimated using the Modification of Diet in Renal Disease study (MDRD) equation for recruitment (but not subsequent analysis) and a study population that was predominantly elderly and white, implying that the results may not be directly applicable to younger populations of more diverse ethnicity.

CONCLUSIONS

Management of CKD in primary care should focus principally on identifying the minority of people at high risk of adverse outcomes, to allow intervention to slow CKD progression and reduce cardiovascular events. Efforts should also be made to identify and reassure the majority who are at low risk of progression to ESKD. Consideration should be given to adopting an age-calibrated definition of CKD to avoid labelling a large group of people with age-related decline in GFR and low associated risk as having CKD.

The epidemiology of hospitalised acute kidney injury not requiring dialysis in England from 1998 to 2013: retrospective analysis of hospital episode statistics

AIMS

Epidemiology studies of acute kidney injury (AKI) have focused on cases requiring dialysis but those not requiring dialysis represent the majority. To address this gap, we interrogated hospital episode statistics (HES) to investigate population trends in temporal epidemiology of AKI not requiring dialysis between 1998 and 2013.

METHODOLOGY

In this retrospective observational study of HES data covering the entire English National Health Service, we identified 1,136,167 AKI events, not requiring dialysis, diagnosed between 1998 and 2013. We explored the effect of age, gender, ethnicity, Charlson's comorbidity score (CCS), method of admission, diagnosis period and AKI in diagnosis codes on temporal changes in the incidence and case-fatality of AKI with specific examination of its predictors.

RESULT

The incidence of AKI increased from 15,463 cases (317 pmp) in 1998-1999 to 213,700 cases (3995 pmp) in 2012-2013. There was increase in proportion of people over 75 years from 51.1% in 1998-1999 to 63.4% in 2012-2013. Overall unadjusted case-fatality decreased from 42.3% in 1998-2003 to 27.1% in 2008-2013, p < 0.001. Compared with 1998-2003, the multivariable adjusted odds ratio for death was 0.64 in 2003-2008 (95% CI 0.63-0.65) and 0.35 in 2008-2013 (95% CI 0.34-0.35). Odds for death were higher for patients over 85 years (2.93; 95% CI 2.89-2.97), CCS of more than five (2.75; 95% CI 2.71-2.79), emergency admissions (2.14; 95% CI 2.09-2.18) and AKI in the secondary diagnosis code (1.35; 95% CI 1.33-1.36) and AKI in other diagnoses codes (2.17; 95% CI 2.15-2.20).

CONCLUSIONS

In England, the incidence of AKI not requiring dialysis has increased and case-fatality has decreased over last 15 years. Efforts to reduce the incidence of AKI and improve survival should focus on elderly people, emergency admissions and those with multi-morbidity.

The burden of comorbidity in people with chronic kidney disease stage 3: a cohort study

BACKGROUND

Multimorbidity is a growing concern for healthcare systems, with many countries experiencing demographic transition to older population profiles. Chronic kidney disease (CKD) is common but often considered in isolation. The extent and prognostic significance of its comorbidities is not well understood. This study aimed to assess the extent and prognostic significance of 11 comorbidities in people with CKD stage 3.

METHODS

A prospective cohort of 1741 people with CKD stage 3 was recruited from primary care between August 2008 and March 2010. Participants underwent medical history, clinical assessment, blood and urine sampling. Comorbidity was defined by self-reported doctor-diagnosed condition, disease-specific medication or blood results (hemoglobin), and treatment burden as number of ongoing medications. Logistic regression was used to identify associations with greater treatment burden (taking >5 medications) and greater multimorbidity (3 or more comorbidities). Kaplan Meier plots and multivariate Cox proportional hazards models were used to investigate associations between multimorbidity and all-cause mortality.

RESULTS

One thousand seven hundred forty-one people were recruited, mean age 72.9 +/-9 years. Mean baseline eGFR was 52 ml/min/1.73 m(2). Only 78/1741 (4 %) had no comorbidities, 453/1741 (26 %) had one, 508/1741 (29 %) had two and 702/1741 (40 %) had >2. Hypertension was common (88 %), 30 % had 'painful condition', 24 % anemia, 23 %, ischaemic heart disease, 17 % diabetes and 12 % thyroid disorders. Median medication use was 5 medications (interquartile range 3-8) and increased with degree of comorbidity. Greater treatment burden and multimorbidity were independently associated with age, smoking, increasing body mass index and decreasing eGFR. Treatment burden was also independently associated with lower education status. After median 3.6 years follow-up, 175/1741 (10 %) died. Greater multimorbidity was independently associated with mortality (hazard ratio 2.81 (95 % confidence intervals 1.72-4.58), p < 0.001) for 3 or more comorbidities vs 0 or 1).

CONCLUSIONS

Isolated CKD was rare and multimorbidity the norm in this cohort of people with moderate CKD. Increasing multimorbidity was associated with greater medication burden and poorer survival. CKD management should include consideration of comorbidities.

Long Term Outcomes after Acute Kidney Injury: Lessons from the ARID Study

The high incidence and poor short-term outcomes of acute kidney injury (AKI) have focused attention on this global healthcare issue. Concurrently, the long-term effects of AKI are increasingly appreciated, namely, increased risk of subsequent chronic kidney disease, end stage kidney disease requiring renal replacement therapies and a higher rate of cardiovascular events. Whilst there is little doubt about the strength of these associations, knowledge gaps remain. To address some of these, the AKI Risk In Derby study commenced in 2013. This is a prospective case-control study investigating the long-term effects of AKI in a general hospitalized population (including those with less severe AKI). This review will summarize the background and rationale of this study, its design and methodology, as well as the 1-year outcome results from a preceding pilot study.

The Association between Polyclonal Combined Serum Free Light Chain Concentration and Mortality in Individuals with Early Chronic Kidney Disease

A major component of increased mortality risk in people with chronic kidney disease (CKD) is associated with non-traditional cardiovascular risk factors including markers of inflammation. We studied whether a novel marker of systemic inflammation, elevated serum combined polyclonal immunoglobulin free light chains (cFLC), was an independent risk factor for increased all-cause mortality in people with CKD stage 3. In a prospective community based cohort study, 1695 participants with stage 3 CKD and no cases of monoclonal gammopathy had cFLC concentrations measured. cFLC levels were determined using the summation of Freelite kappa and lambda assays. All other bioclinical variables were collected at the time of sample collection. Kaplan-Meier plots and Cox proportional hazards analysis was used to assess the relationship between high cFLC levels (>43.3 mg/L) and mortality. There were 167 deaths (10%) after a median of 1375 days. cFLC levels at recruitment were higher in participants who died compared with those who were alive at the end of the study; median: 46.5 mg/L (IQR: 36.1-65.4 mg/L) and 35.4 mg/L (28.1-46.6 mg/L) respectively, P <0.001. Kaplan-Meier survival analysis demonstrated participants with cFLC >43.3 mg/L levels had an increased risk of mortality compared to people with normal cFLC levels (P <0.001). Elevated cFLC levels were independently associated with worse survival (Hazard ratio: 1.50; 95% confidence interval: 1.04-2.16; P=0.03). Other independent risk factors for worse survival were: older age, male gender, previous cardiovascular event, lower eGFR and higher high sensitivity C-reactive protein (hsCRP). To conclude, high cFLC levels predict increased mortality in people with stage 3 CKD, independent of established risk factors and other markers of inflammation.