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1.  Physical Performance and Frailty in Chronic Kidney Disease 
American journal of nephrology  2013;38(4):307-315.
Background
Poor physical performance and frailty are associated with elevated risks of death and disability. Chronic kidney disease (CKD) is also strongly associated with these outcomes. The risks of poor physical performance and frailty among CKD patients, however, are not well established.
Methods
We measured the Short Physical Performance Battery (SPPB, a summary test of gait speed, chair-raises and balance; range 0–12) and the five elements of frailty among 1111 Chronic Renal Insufficiency Cohort participants. Adjusting for demographics and multiple comorbidities, we fit a linear regression model for the outcome of SPPB score and an ordinal logistic regression model for frailty status.
Results
Median (interquartile range [IQR]) age was 65 (57–71) years, median estimated glomerular filtration rate (eGFR) for non-dialysis patients was 49 (36–62) ml/min/1.73m2, and median SPPB score was 9 (7–10). Seven percent of participants were frail and 43% were pre-frail. Compared with the SPPB score for eGFR >60 ml/min/1.73m2, the SPPB was 0.51 points lower for eGFR 30 – 59; 0.61 points lower for eGFR 15 – 29; and 1.75 points lower for eGFR <15; (p<0.01 for all comparisons). eGFR 30 – 59 (OR 1.45; p=0.024), eGFR 15 – 29 (OR 2.02; p=0.002) and eGFR <15 (OR 4.83, p<0.001) were associated with worse frailty status compared with eGFR >60 ml/min/1.73m2.
Conclusions
CKD severity was associated with poor physical performance and frailty in a graded fashion. Future trials should determine if outcomes for CKD patients with frailty and poor physical performance are improved by targeted interventions.
doi:10.1159/000355568
PMCID: PMC4019506  PMID: 24107579
Physical performance; frailty; chronic kidney disease
2.  Metabolic Syndrome, Components, and Cardiovascular Disease Prevalence in Chronic Kidney Disease: Findings from the Chronic Renal Insufficiency Cohort (CRIC) Study 
American Journal of Nephrology  2011;33(6):477-484.
Background/Aims
Metabolic syndrome may increase the risk for incident cardiovascular disease (CVD) and all-cause mortality in the general population. It is unclear whether, and to what degree, metabolic syndrome is associated with CVD in chronic kidney disease (CKD). We determined metabolic syndrome prevalence among individuals with a broad spectrum of kidney dysfunction, examining the role of the individual elements of metabolic syndrome and their relationship to prevalent CVD.
Methods
We evaluated four models to compare metabolic syndrome or its components to predict prevalent CVD using prevalence ratios in the Chronic Renal Insufficiency Cohort (CRIC) Study.
Results
Among 3,939 CKD participants, the prevalence of metabolic syndrome was 65% and there was a significant association with prevalent CVD. Metabolic syndrome was more common in diabetics (87.5%) compared with non-diabetics (44.3%). Hypertension was the most prevalent component, and increased triglycerides the least prevalent. Using the bayesian information criterion, we found that the factors defining metabolic syndrome, considered as a single interval-scaled variable, was the best of four models of metabolic syndrome, both for CKD participants overall and for diabetics and non-diabetics separately.
Conclusion
The predictive value of this model for future CVD outcomes will subsequently be validated in longitudinal analyses.
doi:10.1159/000327618
PMCID: PMC3095834  PMID: 21525746
Cardiovascular disease; Chronic kidney disease; Chronic Renal Insufficiency Cohort (CRIC) Study; Metabolic syndrome
3.  Variability of Creatinine Measurements in Clinical Laboratories: Results from the CRIC Study 
American Journal of Nephrology  2010;31(5):426-434.
Objectives
Estimating equations using serum creatinine (SCr) are often used to assess glomerular filtration rate (GFR). Such creatinine (Cr)-based formulae may produce biased estimates of GFR when using Cr measurements that have not been calibrated to reference laboratories. In this paper, we sought to examine the degree of this variation in Cr assays in several laboratories associated with academic medical centers affiliated with the Chronic Renal Insufficiency Cohort (CRIC) Study; to consider how best to correct for this variation, and to quantify the impact of such corrections on eligibility for participation in CRIC. Variability of Cr is of particular concern in the conduct of CRIC, a large multicenter study of subjects with chronic renal disease, because eligibility for the study depends on Cr-based assessment of GFR.
Methods
A library of 5 large volume plasma specimens from apheresis patients was assembled, representing levels of plasma Cr from 0.8 to 2.4 mg/dl. Samples from this library were used for measurement of Cr at each of the 14 CRIC laboratories repetitively over time. We used graphical displays and linear regression methods to examine the variability in Cr, and used linear regression to develop calibration equations. We also examined the impact of the various calibration equations on the proportion of subjects screened as potential participants who were actually eligible for the study.
Results
There was substantial variability in Cr assays across laboratories and over time. We developed calibration equations for each laboratory; these equations varied substantially among laboratories and somewhat over time in some laboratories. The laboratory site contributed the most to variability (51% of the variance unexplained by the specimen) and variation with time accounted for another 15%. In some laboratories, calibration equations resulted in differences in eligibility for CRIC of as much as 20%.
Conclusions
The substantial variability in SCr assays across laboratories necessitates calibration of SCr measures to a common standard. Failing to do so may substantially affect study eligibility and clinical interpretations when they are determined by Cr-based estimates of GFR.
doi:10.1159/000296250
PMCID: PMC2883847  PMID: 20389058
Chronic renal disease; Creatinine measurements, variability; Chronic Renal Insufficiency Cohort (CRIC) Study; Glomerular filtration rate

Results 1-3 (3)