Faculty Bibliography

BACKGROUND:Intraoperative hemolysis and inflammation are associated with acute kidney injury (AKI) following cardiac surgery. Plasma-free hemoglobin induces heme oxygenase-1 (HO-1) expression. HO-1 degrades heme but increases in experimental models of AKI. This study tested the hypothesis that plasma HO-1 concentrations are associated with intraoperative hemolysis and are increased in patients that develop AKI following cardiac surgery. METHODS:We measured plasma HO-1, free hemoglobin, and inflammatory markers in 74 patients undergoing cardiopulmonary bypass (CPB). AKI was defined as an increase in serum creatinine concentration of 50% or 0.3 mg/dl within 72 h of surgery. RESULTS:Twenty-eight percent of patients developed AKI. HO-1 concentrations increased from 4.2 ± 0.2 ng/ml at baseline to 6.6 ± 0.5 ng/ml on postoperative day (POD) 1 (p < 0.001). POD1 HO-1 concentrations were 3.1 ng/ml higher (95% CI 1.1-5.1) in AKI patients, as was the change in HO-1 from baseline to POD1 (4.4 ± 1.3 ng/ml in AKI patients vs. 1.5 ± 0.3 ng/ml in no-AKI patients, p = 0.006). HO-1 concentrations remained elevated in AKI patients even after controlling for AKI risk factors and preoperative drug therapy. Peak-free hemoglobin concentrations correlated with peak HO-1 concentrations on POD1 in patients that developed AKI (p = 0.02). Duration of CPB and post-CPB IL-6 and IL-10 concentrations were also associated with increased HO-1 on POD1. CONCLUSION/CONCLUSIONS:Plasma HO-1 is increased in patients that develop AKI, and CPB duration, hemolysis, and inflammation are associated with increased HO-1 concentrations following cardiac surgery. Strategies that alter hemolysis and HO-1 expression during cardiac surgery may affect risk for AKI.

OBJECTIVES/OBJECTIVE:To test the hypothesis that low bispectral index scores and low sedative requirements during therapeutic hypothermia predict poor neurologic outcome. DESIGN/METHODS:Observational study of a prospectively collected cohort. SETTING/METHODS:Cardiovascular ICU. PATIENTS/METHODS:One hundred sixty consecutive cardiac arrest patients treated with therapeutic hypothermia. INTERVENTIONS/METHODS:None. MEASUREMENTS AND RESULTS/RESULTS:Eighty-four of the 141 subjects (60%) who survived hypothermia induction were discharged from the ICU with poor neurologic outcome, defined as a cerebral performance category score of 3, 4, or 5. These subjects had lower bispectral index (p < 0.001) and sedative requirements (p < 0.001) during hypothermia compared with the 57 subjects discharged with good outcome. Early prediction of neurologic recovery was best 7 hours after ICU admission, and median bispectral index scores at that time were 31 points lower in subjects discharged with poor outcome (11 [interquartile range, 4-29] vs 42 [37-49], p < 0.001). Median sedation requirements decreased by 17% (interquartile range, -50 to 0%) 7 hours after ICU admission in subjects with poor outcome but increased by 50% (interquartile range, 0-142%) in subjects with good outcome (p < 0.001). Each 10-point decrease in bispectral index was independently associated with a 59% increase in the odds of poor outcome (95% CI, 32-76%; p < 0.001). The model including bispectral index and sedative requirement correctly reclassified 15% of subjects from good to poor outcome and 1% of subjects from poor to good outcome. The model incorrectly reclassified 1% of subjects from poor to good outcome but did not incorrectly reclassify any from good to poor outcome. CONCLUSIONS:Bispectral index scores and sedative requirements early in the course of therapeutic hypothermia improve the identification of patients who will not recover from brain anoxia. The ability to accurately predict nonrecovery after cardiac arrest could facilitate discussions with families, reduce patient suffering, and limit use of ICU resources in futile cases.

We examined racial differences in gout incidence among black and white participants in a longitudinal, population-based cohort and tested whether racial differences were explained by higher levels of serum urate. The Atherosclerosis Risk in Communities Study is a prospective, US population-based cohort study of middle-aged adults enrolled between 1987 and 1989 with ongoing annual follow-up through 2012. We estimated the adjusted hazard ratios and 95% confidence intervals of incident gout by race among 11,963 men and women using adjusted Cox proportional hazards models. The cohort was 23.6% black. The incidence rate of gout was 8.4 per 10,000 person-years (15.5/10,000 person-years for black men, 12.0/10,000 person-years for black women, 9.4/10,000 person-years for white men, and 5.0/10,000 person-years for white women; P < 0.001). Black participants had an increased risk of incident gout (for women, adjusted hazard ratio (HR) = 1.69, 95% confidence interval (CI): 1.29, 2.22; for men, adjusted HR = 1.92, 95% CI: 1.44, 2.56). Upon further adjustment for uric acid levels, there was modest attenuation of the association of race with incident gout (for women, adjusted HR = 1.62, 95% CI: 1.24, 2.22; for men, adjusted HR = 1.49, 95% CI: 1.11, 2.00) compared with white participants. In this US population-based cohort, black women and black men were at increased risk of developing gout during middle and older ages compared with whites, which appears, particularly in men, to be partly related to higher urate levels in middle-aged blacks.

Smoking is the leading cause of preventable death in the United States. Studies have shown that smoking status tends to be concordant within spouse pairs. This study aimed to estimate the association of spousal smoking status with quitting smoking in US adults. We analyzed data from 4,500 spouse pairs aged 45-64 years from the Atherosclerosis Risk in Communities Study cohort, sampled from 1986 to 1989 from 4 US communities and followed up every 3 years for a total of 9 years. Logistic regression with generalized estimating equations was used to calculate the odds ratio of quitting smoking given that one's spouse is a former smoker or a current smoker compared to a never smoker. Among men and women, being married to a current smoker decreased the odds of quitting smoking (for men, odds ratio (OR) = 0.37, 95% confidence interval (CI): 0.29, 0.46; for women, OR = 0.54, 95% CI: 0.43, 0.68). Among women only, being married to a former smoker increased the odds of quitting smoking (OR = 1.26, 95% CI: 1.04, 1.53). In conclusion, spouses of current smokers are less likely to quit, whereas women married to former smokers are more likely to quit. Smoking cessation programs and clinical advice should consider targeting couples rather than individuals.

Some observational studies have identified elevated uric acid concentration as a risk factor for diabetes, while others have found an inverse relationship. We examined both the association of uric acid level with incident diabetes and the change in uric acid concentration after a diabetes diagnosis. We analyzed data from the Atherosclerosis Risk in Communities (ARIC) Study and quantified the independent association between uric acid level and incident diabetes via Cox proportional hazards models. The association between duration of diabetes and change in uric acid level was examined via linear regression. Among 11,134 participants without diagnosed diabetes at baseline (1987-1989), there were 1,294 incident cases of diabetes during a median of 9 years of follow-up (1987-1998). Uric acid level was associated with diabetes even after adjustment for risk factors (per 1 mg/dL, hazard ratio = 1.18, 95% confidence interval: 1.13, 1.23), and the association remained significant after adjustment for fasting glucose and insulin levels. Among participants with diabetes (n = 1,510), every additional 5 years' duration of diabetes was associated with a 0.10-mg/dL (95% confidence interval: 0.04, 0.15) lower uric acid level after adjustment. We conclude that uric acid concentration rises prior to diagnosis of diabetes and then declines with diabetes duration. Future studies investigating uric acid as a risk factor for cardiovascular disease should adequately account for the impact and timing of diabetes development.

BACKGROUND:In epidemiologic research, incident chronic kidney disease (CKD) commonly is determined by laboratory tests performed at planned study visits. Given the morbidity and mortality associated with CKD, persons with incident disease may be less likely to attend scheduled visits, affecting observed associations. The objective of this study was to quantify loss to follow-up by CKD status and determine whether supplementation with diagnostic code data improves capture of incident CKD. STUDY DESIGN/METHODS:Prospective cohort study. SETTING & PARTICIPANTS/METHODS:11,560 participants in the Atherosclerosis Risk in Communities (ARIC) Study underwent continuous surveillance for hospitalizations and death from baseline visit (1996-1999) to follow-up visit (2011-2013). A subset of hospitalizations in Washington County, MD, was used in diagnostic code validation (n=2,540). PREDICTOR/METHODS:Baseline demographics and comorbid conditions. OUTCOMES/RESULTS:Incident CKD stage 3 ascertained by follow-up visit (visit-based definition) or hospitalization surveillance (hospitalization-based definition). MEASUREMENTS/METHODS:Visit-based definition: ≥25% decline from baseline estimated glomerular filtration rate to <60 mL/min/1.73 m2 at follow-up visit; hospitalization-based definition: hospitalization CKD diagnostic code. RESULTS:Of 11,560 participants, 5,951 attended the follow-up visit and 9,264 were hospitalized. Never-hospitalized participants were younger, more often female, and had fewer comorbid conditions; 73.5% attended the follow-up visit. Incident CKD stage 3 occurred in 1,172 participants by the visit-based definition (251 were never hospitalized) and 1,078 participants by the hospitalization-based definition (237 attended the follow-up study visit). Sensitivity of the hospitalization-based CKD definition was 35.5% (95% CI, 31.6%-39.7%); specificity was 95.7% (95% CI, 94.2%-96.8%). Sensitivity was higher with later time period, older participant age, and baseline prevalent diabetes and CKD. LIMITATIONS/CONCLUSIONS:A subset of hospitalizations was used for validation; 15-year gap between study visits. CONCLUSIONS:The sensitivity of diagnostic code-identified CKD is low and varies by certain factors; however, supplementing a visit-based definition with hospitalization information can increase disease identification during periods of follow-up without study visits.

BACKGROUND:Persons with chronic kidney disease (CKD) are at high risk for cardiovascular disease events, but are not classified as such in current US cholesterol treatment guidelines. We examined potential effects of modified guidelines in which CKD was considered a "coronary heart disease (CHD) risk equivalent" for risk stratification. STUDY DESIGN/METHODS:Nationally representative cross-sectional study. SETTING & PARTICIPANTS/METHODS:4,823 adults 20 years or older from the 2007-2010 National Health and Nutrition Examination Survey. PREDICTORS/METHODS:Cardiovascular risk stratification based on current US cholesterol treatment guidelines and 2 simulated scenarios in which CKD stages 3-5 or CKD stages 1-5 were considered a CHD risk equivalent. OUTCOMES & MEASUREMENTS/METHODS:Proportion of persons with low-density lipoprotein (LDL) cholesterol at levels above treatment targets and above the threshold for lipid-lowering therapy initiation, based on current guidelines and the 2 simulated scenarios. RESULTS:Under current guidelines, 55.1 million adults in 2010 did not achieve the target LDL cholesterol goal. Of these, 25.2 million had sufficiently elevated levels to meet recommendations for initiating lipid-lowering therapy; 12.1 million were receiving this therapy but remained above goal. When CKD stages 3-5 were considered a CHD risk equivalent, 59.2 million persons were above target LDL cholesterol goals, with 28.5 million and 13.3 million meriting therapy initiation and intensification, respectively. When CKD stages 1-5 were considered a CHD risk equivalent, 65.2 million adults were above goal, with 33.9 million and 14.4 million meriting therapy initiation and intensification, respectively. LIMITATIONS/CONCLUSIONS:CKD and LDL cholesterol defined using a single laboratory value. CONCLUSIONS:Many adults in the United States currently do not meet recommended goals for LDL cholesterol levels. Modifying the current cholesterol guidelines to include CKD as a CHD risk equivalent would lead to a substantial increase in both the number of persons with levels above LDL cholesterol treatment targets and those recommended to initiate lipid-lowering therapy.

OBJECTIVE Serum cystatin C is an alternative to serum creatinine for estimating glomerular filtration rate (GFR), since cystatin C is less influenced by age and muscle mass. Among persons with diabetes, we compared the performance of GFR estimated using cystatin C (eGFRcys) with that using creatinine (eGFRcr) for the identification of reduced kidney function and its association with diabetes complications. RESEARCH DESIGN AND METHODS We analyzed data from adult participants from the 1999-2002 National Health and Nutrition Examination Survey with available cystatin C (N = 4,457). Kidney function was dichotomized as preserved (eGFR ≥60 mL/min/1.73 m(2)) or reduced (eGFR <60 mL/min/1.73 m(2)) using the 2012 Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) cystatin C and the 2009 CKD-EPI creatinine equations. RESULTS Among 778 persons with diabetes, the prevalence of reduced kidney function was 16.5% using eGFRcr and 22.0% using eGFRcys. More persons with diabetes were reclassified from preserved kidney function by eGFRcr to reduced kidney function by eGFRcys than persons without diabetes (odds ratio 3.1 [95% CI 1.9-4.9], P < 0.001). The associations between lower eGFR and higher prevalence of albuminuria, retinopathy, peripheral arterial disease, and coronary artery disease were robust regardless of filtration marker. Similarly, the risk of all-cause mortality increased with lower eGFRcr and eGFRcys. Only lower eGFRcys was significantly associated with cardiovascular mortality. CONCLUSIONS More persons with diabetes had reduced kidney function by eGFRcys than by eGFRcr, and lower eGFRcys was strongly associated with diabetes complications. Whether eGFRcys is superior to eGFRcr in approximating true kidney function in a diabetic population requires additional study.

BACKGROUND AND OBJECTIVES/OBJECTIVE:Billing codes are frequently used to identify AKI events in epidemiologic research. The goals of this study were to validate billing code-identified AKI against the current AKI consensus definition and to ascertain whether sensitivity and specificity vary by patient characteristic or over time. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS/METHODS:The study population included 10,056 Atherosclerosis Risk in Communities study participants hospitalized between 1996 and 2008. Billing code-identified AKI was compared with the 2012 Kidney Disease Improving Global Outcomes (KDIGO) creatinine-based criteria (AKIcr) and an approximation of the 2012 KDIGO creatinine- and urine output-based criteria (AKIcr_uop) in a subset with available outpatient data. Sensitivity and specificity of billing code-identified AKI were evaluated over time and according to patient age, race, sex, diabetes status, and CKD status in 546 charts selected for review, with estimates adjusted for sampling technique. RESULTS:A total of 34,179 hospitalizations were identified; 1353 had a billing code for AKI. The sensitivity of billing code-identified AKI was 17.2% (95% confidence interval [95% CI], 13.2% to 21.2%) compared with AKIcr (n=1970 hospitalizations) and 11.7% (95% CI, 8.8% to 14.5%) compared with AKIcr_uop (n=1839 hospitalizations). Specificity was >98% in both cases. Sensitivity was significantly higher in the more recent time period (2002-2008) and among participants aged 65 years and older. Billing code-identified AKI captured a more severe spectrum of disease than did AKIcr and AKIcr_uop, with a larger proportion of patients with stage 3 AKI (34.9%, 19.7%, and 11.5%, respectively) and higher in-hospital mortality (41.2%, 18.7%, and 12.8%, respectively). CONCLUSIONS:The use of billing codes to identify AKI has low sensitivity compared with the current KDIGO consensus definition, especially when the urine output criterion is included, and results in the identification of a more severe phenotype. Epidemiologic studies using billing codes may benefit from a high specificity, but the variation in sensitivity may result in bias, particularly when trends over time are the outcome of interest.

BACKGROUND:There is uncertainty regarding treatment of hypertension in hemodialysis patients due to the observed J-shaped association between blood pressure (BP) and death. We hypothesized that this association reflects confounding by cardiovascular disease (CVD) and that stratification by CVD biomarkers, cardiac troponin I (cTnI) and N-terminal fragment of prohormone brain natriuretic peptide (NT-proBNP), might change this association. STUDY DESIGN/METHODS:National prospective cohort study. SETTING & PARTICIPANTS/METHODS:446 incident hemodialysis patients. PREDICTOR/METHODS:Predialysis systolic BP. OUTCOMES/RESULTS:Mortality (all-cause and CVD) and first CVD event assessed using Cox regression adjusted for demographics, comorbid conditions, and clinical factors. MEASUREMENTS/METHODS:Participants with cTnI level ≥0.1 ng/mL or NT-proBNP level ≥9,252 pg/mL were classified as the high-biomarker group; remaining participants were included in the low-biomarker group. RESULTS:Participants in the high-biomarker group (n=138 [31%]) were older (61 vs. 57 years) and had a higher prevalence of CVD (67% vs. 23%), but similar baseline BPs (152 vs. 153 mm Hg). There were 323 deaths (143 from CVD) and 271 CVD events. The high-biomarker group had a higher risk of mortality than the low-biomarker group (HR, 1.75; 95% CI, 1.37-2.24). The association between BP and outcomes differed between the 2 biomarker groups (P for interaction=0.01, 0.2, and 0.07 for all-cause mortality, CVD mortality, and first CVD event, respectively). In the low-biomarker group, BP was associated with greater risk of outcomes: HR per 10 mm Hg higher BP was 1.07 (95% CI, 1.01-1.14), 1.10 (95% CI, 0.96-1.25), and 1.04 (95% CI, 0.96-1.13) for all-cause mortality, CVD mortality, and first CVD event, respectively. Importantly, lower BP was not associated with increased risk of outcomes in stratified models, including for those in high biomarker group. LIMITATIONS/CONCLUSIONS:BP measurements not standardized. CONCLUSIONS:The observed J-shaped association between BP and outcomes in hemodialysis patients is due to confounding by subclinical CVD. A stratification approach based on cTnI and NT-proBNP levels has the potential to inform BP treatment in hemodialysis patients.