Case-cohort Study Design Research Articles

Physical activity and the risk of preterm birth: a systematic review and meta‐analysis of epidemiological studies

Physical activity has been inconsistently associated with risk of preterm birth, and the strength of the association and the shape of the dose-response relationship needs clarification. To conduct a systematic review and dose-response meta-analysis to clarify the association between physical activity and risk of preterm birth. PubMed, Embase and Ovid databases were searched for relevant studies up to 9 February 2017. Studies with a prospective cohort, case-cohort, nested case-control or randomized study design were included. Data were extracted by one reviewer and checked for accuracy by a second reviewer. Summary relative risks (RRs) were estimated using a random effects model. Forty-one studies (43 publications) including 20 randomized trials and 21 cohort studies were included. The summary RR for high versus low activity was 0.87 [95% confidence interval (CI): 0.70-1.06, I2 = 17%, n = 5] for physical activity before pregnancy, and it was 0.86 (95% CI: 0.78-0.95, I2 = 0%, n = 30) for early pregnancy physical activity. The summary RR for a 3 hours per week increment in leisure-time activity was 0.90 (95% CI: 0.85-0.95, I2 = 0%, n = 5). There was evidence of a nonlinear association between physical activity and preterm birth, Pnonlinearity < 0.0001, with the lowest risk observed at 2-4 hours per week of activity. This meta-analysis suggests that higher leisure-time activity is associated with reduced risk of preterm birth. Further randomized controlled trials with sufficient frequency and duration of activity to reduce the risk and with larger sample sizes are needed to conclusively demonstrate an association. Physically active compared with inactive women have an 10-14% reduction in the risk of preterm birth.

The Hokkaido Birth Cohort Study on Environment and Children\u2019s Health: cohort profile\u2014updated 2017

The Hokkaido Study on Environment and Children’s Health is an ongoing study consisting of two birth cohorts of different population sizes: the Sapporo cohort and the Hokkaido cohort. Our primary study goals are (1) to examine the effects of low-level environmental chemical exposures on birth outcomes, including birth defects and growth retardation; (2) to follow the development of allergies, infectious diseases, and neurobehavioral developmental disorders and perform a longitudinal observation of child development; (3) to identify high-risk groups based on genetic susceptibility to environmental chemicals; and (4) to identify the additive effects of various chemicals, including tobacco smoking. The purpose of this report is to update the progress of the Hokkaido Study, to summarize the recent results, and to suggest future directions. In particular, this report provides the basic characteristics of the cohort populations, discusses the population remaining in the cohorts and those who were lost to follow-up at birth, and introduces the newly added follow-up studies and case-cohort study design. In the Sapporo cohort of 514 enrolled pregnant women, various specimens, including maternal and cord blood, maternal hair, and breast milk, were collected for the assessment of exposures to dioxins, polychlorinated biphenyls, organochlorine pesticides, perfluoroalkyl substances, phthalates, bisphenol A, and methylmercury. As follow-ups, face-to-face neurobehavioral developmental tests were conducted at several different ages. In the Hokkaido cohort of 20,926 enrolled pregnant women, the prevalence of complicated pregnancies and birth outcomes, such as miscarriage, stillbirth, low birth weight, preterm birth, and small for gestational age were examined. The levels of exposure to environmental chemicals were relatively low in these study populations compared to those reported previously. We also studied environmental chemical exposure in association with health outcomes, including birth size, neonatal hormone levels, neurobehavioral development, asthma, allergies, and infectious diseases. In addition, genetic and epigenetic analyses were conducted. The results of this study demonstrate the effects of environmental chemical exposures on genetically susceptible populations and on DNA methylation. Further study and continuous follow-up are necessary to elucidate the combined effects of chemical exposure on health outcomes.

A comparison of Cox and logistic regression for use in genome-wide association studies of cohort and case-cohort design

Logistic regression is often used instead of Cox regression to analyse genome-wide association studies (GWAS) of single-nucleotide polymorphisms (SNPs) and disease outcomes with cohort and case-cohort designs, as it is less computationally expensive. Although Cox and logistic regression models have been compared previously in cohort studies, this work does not completely cover the GWAS setting nor extend to the case-cohort study design. Here, we evaluated Cox and logistic regression applied to cohort and case-cohort genetic association studies using simulated data and genetic data from the EPIC-CVD study. In the cohort setting, there was a modest improvement in power to detect SNP–disease associations using Cox regression compared with logistic regression, which increased as the disease incidence increased. In contrast, logistic regression had more power than (Prentice weighted) Cox regression in the case-cohort setting. Logistic regression yielded inflated effect estimates (assuming the hazard ratio is the underlying measure of association) for both study designs, especially for SNPs with greater effect on disease. Given logistic regression is substantially more computationally efficient than Cox regression in both settings, we propose a two-step approach to GWAS in cohort and case-cohort studies. First to analyse all SNPs with logistic regression to identify associated variants below a pre-defined P-value threshold, and second to fit Cox regression (appropriately weighted in case-cohort studies) to those identified SNPs to ensure accurate estimation of association with disease.

Case-cohort studies with interval-censored failure time data.

The case-cohort design has been widely used as a means of cost reduction in assembling or measuring expensive covariates in large cohort studies. The existing literature on the case-cohort design is mainly focused on right-censored data. In practice, however, the failure time is often subject to interval-censoring; it is known only to fall within some random time interval. In this paper, we consider the case-cohort study design for interval-censored failure time and develop a sieve semiparametric likelihood approach for analyzing data from this design under the proportional hazards model. We construct the likelihood function using inverse probability weighting and build the sieves with Bernstein polynomials. The consistency and asymptotic normality of the resulting regression parameter estimator are established and a weighted bootstrap procedure is considered for variance estimation. Simulations show that the proposed method works well for practical situations, and an application to real data is provided.

Improving efficiency of parameter estimation in case-cohort studies with multivariate failure time data.

The case-cohort study design is an effective way to reduce cost of assembling and measuring expensive covariates in large cohort studies. Recently, several weighted estimators were proposed for the case-cohort design when multiple diseases are of interest. However, these existing weighted estimators do not make effective use of the covariate information available in the whole cohort. Furthermore, the auxiliary information for the expensive covariates, which may be available in the studies, cannot be incorporated directly. In this article, we propose a class of updated-estimators. We show that, by making effective use of the whole cohort information, the proposed updated-estimators are guaranteed to be more efficient than the existing weighted estimators asymptotically. Furthermore, they are flexible to incorporate the auxiliary information whenever available. The advantages of the proposed updated-estimators are demonstrated in simulation studies and a real data analysis.

More efficient estimators for marginal additive hazards model in case-cohort studies with multiple outcomes

Case-cohort study designs are widely used to reduce the cost of large cohort studies. When several diseases are of interest, we can use the same subcohort. In this paper, we will study the casecohort design of marginal additive hazards model for multiple outcomes by a more efficient version. Instead of analyzing each disease separately, ignoring the additional exposure measurements collected on subjects with other diseases, we propose a new weighted estimating equation approach to improve the efficiency by utilizing as much information collected as possible. The consistency and asymptotic normality of the resulting estimator are established. Simulation studies are conducted to examine the finite sample performance of the proposed estimator, which confirm the efficiency gains.

Vitamin D deficiency and incident stroke risk in community-living black and white adults.

Black individuals are at greater risk of stroke and vitamin D deficiency than white individuals. Epidemiologic studies have shown that low 25-hydroxyvitamin D concentrations are associated with increased risk of stroke, but these studies had limited representation of black individuals. We examined the association of 25-hydroxyvitamin D with incident stroke in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study, a cohort of black and white adults ≥45 years of age. Using a case-cohort study design, plasma 25-hydroxyvitamin D was measured in 610 participants who developed incident stroke (cases) and in 937 stroke-free individuals from a stratified cohort random sample of REGARDS participants (comparison cohort). In multivariable models adjusted for socio-demographic factors, co-morbidities and laboratory values including parathyroid hormone, lower 25-hydroxyvitamin D concentrations were associated with higher risk of stroke (25-hydroxyvitamin D >30 ng/mL reference; 25-hydroxyvitamin D concentrations 20-30 ng/mL, hazard ratio 1.33, 95% confidence interval (95% CI) 0.89,1.96; 25-hydroxyvitamin D <20 ng/mL, hazard ratio 1.85, 95% CI 1.17, 2.93). There were no statistically significant differences in the association of lower 25-hydroxyvitamin D with higher risk of stroke in black vs. white participants in fully adjusted models (hazard ratio comparing lowest vs. highest 25-hydroxyvitamin D category 2.62, 95% CI 1.18, 5.83 in blacks vs. 1.64, 95% CI 0.83, 3.24 in whites, P(interaction) = 0.82). The associations were qualitatively unchanged when restricted to ischemic or hemorrhagic stroke subtypes or when using race-specific cut-offs for 25-hydroxyvitamin D categories. Vitamin D deficiency is a risk factor for incident stroke and the strength of this association does not appear to differ by race.

Urine Injury Biomarkers and Risk of Adverse Outcomes in Recipients of Prevalent Kidney Transplants: The Folic Acid for Vascular Outcome Reduction in Transplantation Trial.

Recipients of kidney transplants (KTR) are at increased risk for cardiovascular events, graft failure, and death. It is unknown whether urine kidney injury biomarkers are associated with poor outcomes among KTRs. We conducted a post hoc analysis of the Folic Acid for Vascular Outcome Reduction in Transplantation (FAVORIT) Trial using a case-cohort study design, selecting participants with adjudicated cardiovascular events, graft failure, or death. Urine neutrophil gelatinase-associated lipocalin (NGAL), kidney injury molecule-1 (KIM-1), IL-18, and liver-type fatty acid binding protein (L-FABP) were measured in spot urine samples and standardized to urine creatinine concentration. We adjusted for demographics, cardiovascular risk factors, eGFR, and urine albumin-to-creatinine ratio. Patients had 291 cardiovascular events, 257 graft failure events, and 359 deaths. Each log increase in urine NGAL/creatinine independently associated with a 24% greater risk of cardiovascular events (adjusted hazard ratio [aHR], 1.24; 95% confidence interval [95% CI], 1.06 to 1.45), a 40% greater risk of graft failure (aHR, 1.40; 95% CI, 1.16 to 1.68), and a 44% greater risk of death (aHR, 1.44; 95% CI, 1.26 to 1.65). Urine KIM-1/creatinine and IL-18/creatinine independently associated with greater risk of death (aHR, 1.29; 95% CI, 1.03 to 1.61 and aHR, 1.25; 95% CI, 1.04 to 1.49 per log increase, respectively) but not with risk of cardiovascular events or graft failure. Urine L-FABP did not associate with any study outcomes. In conclusion, among prevalent KTRs, higher urine NGAL, KIM-1, and IL-18 levels independently and differentially associated with greater risk of adverse outcomes.

Improving the efficiency of estimation in the additive hazards model for stratified case-cohort design with multiple diseases.

The case-cohort study design has often been used in studies of a rare disease or for a common disease with some biospecimens needing to be preserved for future studies. A case-cohort study design consists of a random sample, called the subcohort, and all or a portion of the subjects with the disease of interest. One advantage of the case-cohort design is that the same subcohort can be used for studying multiple diseases. Stratified random sampling is often used for the subcohort. Additive hazards models are often preferred in studies where the risk difference, instead of relative risk, is of main interest. Existing methods do not use the available covariate information fully. We propose a more efficient estimator by making full use of available covariate information for the additive hazards model with data from a stratified case-cohort design with rare (the traditional situation) and non-rare (the generalized situation) diseases. We propose an estimating equation approach with a new weight function. The proposed estimators are shown to be consistent and asymptotically normally distributed. Simulation studies show that the proposed method using all available information leads to efficiency gain and stratification of the subcohort improves efficiency when the strata are highly correlated with the covariates. Our proposed method is applied to data from the Atherosclerosis Risk in Communities study.

Predictors of Venous Thromboembolism Recurrence, Adjusted for Treatments and Interim Exposures: A Population-based Case-cohort Study

BackgroundPredictors of venous thromboembolism (VTE) recurrence are uncertain. ObjectiveTo identify predictors of VTE recurrence, adjusted for treatments and interim exposures. Materials and MethodsUsing Rochester Epidemiology Project resources, all Olmsted County, MN residents with objectively-diagnosed incident VTE over the 13-year period, 1988–2000, who survived ≥1day were followed for first objectively-diagnosed VTE recurrence. For all patients with recurrence, and a random sample of all surviving incident VTE patients (n=415), we collected demographic and baseline characteristics, treatments and interim exposures. In a case-cohort study design, demographic, baseline, treatment and interim exposure characteristics were tested as potential predictors of VTE recurrence using time-dependent Cox proportional hazards modeling. ResultsAmong 1262 incident VTE patients, 306 developed recurrence over 6,440 person-years. Five-year recurrence rates, overall and for cancer-associated, idiopathic and non-cancer secondary VTE, were 24.5%, 43.4%, 27.3% and 18.1%, respectively. In multivariable analysis, interim hospitalization, active cancer, pregnancy, central venous catheter and respiratory infection were associated with increased hazards of recurrence, and warfarin and aspirin were associated with reduced hazards. Adjusting for treatments and these interim risk factors, male sex, baseline active cancer and failure to achieve a therapeutic aPTT in the first 24hours were independently associated with increased hazards of VTE recurrence over the entire follow-up period, while the hazards of recurrence for patient age, chronic lung disease, leg paresis, prior superficial vein thrombosis and idiopathic VTE varied over the follow-up period. ConclusionsBaseline and interim exposures can stratify VTE recurrence risk and may be useful for directing secondary prophylaxis.

Tissue-based Genomics Augments Post-prostatectomy Risk Stratification in a Natural History Cohort of Intermediate- and High-Risk Men

BackgroundRadical prostatectomy (RP) is a primary treatment option for men with intermediate- and high-risk prostate cancer. Although many are effectively cured with local therapy alone, these men are by definition at higher risk of adverse pathologic features and clinical disease recurrence. It has been shown that the Decipher test predicts metastatic progression in cohorts that received adjuvant and salvage therapy following RP. ObjectiveTo evaluate the Decipher genomic classifier in a natural history cohort of men at risk who received no additional treatment until the time of metastatic progression. Design, setting, and participantsRetrospective case-cohort design for 356 men who underwent RP between 1992 and 2010 at intermediate or high risk and received no additional treatment until the time of metastasis. Participants met the following criteria: (1) Cancer of the Prostate Risk Assessment postsurgical (CAPRA-S) score ≥3; (2) pathologic Gleason score ≥7; and (3) post-RP prostate-specific antigen nadir <0.2 ng/ml. Outcome measurements and statistical analysisThe primary endpoint was defined as regional or distant metastases. Time-dependent receiver operating characteristic (ROC) curves, extension of decision curve analysis to survival data, and univariable and multivariable Cox proportional-hazards models were used to measure the discrimination, net benefit, and prognostic potential of genomic and pathologic risk factors. Cumulative incidence curves were constructed using Fine-Gray competing-risks analysis with appropriate weighting of the controls to account for the case-cohort study design. Results and limitationsNinety six patients had unavailable tumor blocks or failed microarray quality control. Decipher scores were then obtained for 260 patients, of whom 99 experienced metastasis. Decipher correlated with increased cumulative incidence of biochemical recurrence, metastasis, and prostate cancer–specific mortality (p<0.01). The cumulative incidence of metastasis was 12% and 47% for patients with low and high Decipher scores, respectively, at 10 yr after RP. Decipher was independently prognostic of metastasis in multivariable analysis (hazard ratio 1.26 per 10% increase; p<0.01). Decipher had a c-index of 0.76 and increased the c-index of Eggener and CAPRA-S risk models from 0.76 and 0.77 to 0.86 and 0.87, respectively, at 10 yr after RP. Although the cohort was large, the single-center retrospective design is an important limitation. ConclusionsIn a patient population that received no adjuvant or salvage therapy after prostatectomy until metastatic progression, higher Decipher scores correlated with clinical events, and inclusion of Decipher scores improved the prognostic performance of validated clinicopathologic risk models. These results confirm the utility already reported for Decipher. Patient summaryThe Decipher test improves identification of patients most at risk of metastatic progression and death from prostate cancer after radical prostatectomy.

Hip Fractures Risk in Older Men and Women Associated With DXA-Derived Measures of Thigh Subcutaneous Fat Thickness, Cross-Sectional Muscle Area, and Muscle Density.

Mid-thigh cross-sectional muscle area (CSA), muscle attenuation, and greater trochanter soft tissue thickness have been shown to be independent risk factors of hip fracture. Our aim was to determine whether muscle and adipose tissue measures derived from dual-energy X-ray absorptiometry (DXA) scans would have a similar risk association as those measured using other imaging methods. Using a case-cohort study design, we identified 169 incident hip fracture cases over an average of 13.5 years among participants from the Health ABC Study, a prospective study of 3075 individuals initially aged 70 to 79 years. We modeled the thigh 3D geometry and compared DXA and computed tomography (CT) measures. DXA-derived thigh CSA, muscle attenuation, and subcutaneous fat thickness were found to be highly correlated to their CT counterparts (Pearson's r = 0.82, 0.45, and 0.91, respectively; p < 0.05). The fracture risk of men and women were calculated separately. We found that decreased subcutaneous fat, CT thigh muscle attenuation, and appendicular lean mass by height squared (ALM/Ht(2)) were associated with fracture risk in men; hazard ratios (HR) = 1.44 (1.02, 2.02), 1.40 (1.05, 1.85), and 0.58 (0.36, 0.91), respectively, after adjusting for age, race, clinical site, body mass index (BMI), chronic disease, hip bone mineral density (BMD), self-reported health, alcohol use, smoking status, education, physical activity, and cognitive function. In a similar model for women, only decreases in subcutaneous fat and DXA CSA were associated with hip fracture risk; HR = 1.39 (1.07, 1.82) and 0.78 (0.62, 0.97), respectively. Men with a high ALM/Ht(2) and low subcutaneous fat thickness had greater than 8 times higher risk for hip fracture compared with those with low ALM/Ht(2) and high subcutaneous fat. In women, ALM/Ht(2) did not improve the model when subcutaneous fat was included. We conclude that the DXA-derived subcutaneous fat thickness is a strong marker for hip fracture risk in both men and women, especially in men with high ALM/Ht(2).

Fibroblast growth factor 23 and risk of incident stroke in community-living adults.

Fibroblast growth factor 23 (FGF23) is a hormone that regulates phosphorus and vitamin D metabolism. Elevated FGF23 concentrations are associated with excess risk of cardiovascular disease. Associations of FGF23 with stroke outcomes are less clear. Using a case-cohort study design, we examined the association of baseline plasma FGF23 concentrations with incident stroke in the Reasons for Geographic and Racial Differences in Stroke (REGARDS) study, a cohort of black and white adults aged ≥45 years. FGF23 was measured in 615 participants who developed incident stroke (cases) and in 936 participants randomly selected from the REGARDS cohort (comparison subcohort). In multivariable-adjusted models, higher calcium and phosphorus concentrations, lower estimated glomerular filtration rate and higher urine albumin excretion were independently associated with higher FGF23. There was no statistically significant association of FGF23 with risk of all-cause stroke in Cox models adjusted for demographic factors and established stroke risk factors (hazard ratio comparing fourth with first quartile 1.19; 95% confidence interval, 0.78-1.82). In prespecified models stratified by stroke subtypes, there was a graded association of FGF23 with risk of cardioembolic stroke in fully adjusted models (quartile 1, reference; quartile 2 hazard ratio, 1.48; 95% confidence interval, 0.63-3.47; quartile 3 hazard ratio, 1.99; 95% confidence interval, 0.89-4.44; quartile 4 hazard ratio, 2.52; 95% confidence interval, 1.08-5.91). There were no statistically significant associations of FGF23 with other ischemic stroke subtypes or with hemorrhagic strokes. Higher FGF23 concentrations were associated with higher risk of cardioembolic but not with other stroke subtypes in community-dwelling adults. Additional studies should delineate reasons for these findings.

Serum IgG antibody levels to periodontal microbiota are associated with incident Alzheimer disease.

BackgroundPeriodontitis and Alzheimer disease (AD) are associated with systemic inflammation. This research studied serum IgG to periodontal microbiota as possible predictors of incident AD.MethodsUsing a case-cohort study design, 219 subjects (110 incident AD cases and 109 controls without incident cognitive impairment at last follow-up), matched on race-ethnicity, were drawn from the Washington Heights-Inwood Columbia Aging Project (WHICAP), a cohort of longitudinally followed northern Manhattan residents aged >65 years. Mean follow-up was five years (SD 2.6). In baseline sera, serum IgG levels were determined for bacteria known to be positively or negatively associated with periodontitis (Porphyromonas gingivalis, Tannerella forsythia, Actinobacillus actinomycetemcomitans Y4, Treponema denticola, Campylobacter rectus, Eubacterium nodatum, and Actinomyces naeslundii genospecies-2). In all analyses, we used antibody threshold levels shown to correlate with presence of moderate-severe periodontitis.ResultsMean age was 72 years (SD 6.9) for controls, and 79 years (SD 4.6) for cases (p<0.001). Non-Hispanic Whites comprised 26%, non-Hispanic Blacks 27%, and Hispanics 48% of the sample. In a model adjusting for baseline age, sex, education, diabetes mellitus, hypertension, smoking, prior history of stroke, and apolipoprotein E genotype, high anti-A. naeslundii titer (>640 ng/ml, present in 10% of subjects) was associated with increased risk of AD (HR = 2.0, 95%CI: 1.1–3.8). This association was stronger after adjusting for other significant titers (HR = 3.1, 95%CI: 1.5–6.4). In this model, high anti-E. nodatum IgG (>1755 ng/ml; 19% of subjects) was associated with lower risk of AD (HR = 0.5, 95%CI: 0.2–0.9).ConclusionsSerum IgG levels to common periodontal microbiota are associated with risk for developing incident AD.

A review of published analyses of case-cohort studies and recommendations for future reporting.

The case-cohort study design combines the advantages of a cohort study with the efficiency of a nested case-control study. However, unlike more standard observational study designs, there are currently no guidelines for reporting results from case-cohort studies. Our aim was to review recent practice in reporting these studies, and develop recommendations for the future. By searching papers published in 24 major medical and epidemiological journals between January 2010 and March 2013 using PubMed, Scopus and Web of Knowledge, we identified 32 papers reporting case-cohort studies. The median subcohort sampling fraction was 4.1% (interquartile range 3.7% to 9.1%). The papers varied in their approaches to describing the numbers of individuals in the original cohort and the subcohort, presenting descriptive data, and in the level of detail provided about the statistical methods used, so it was not always possible to be sure that appropriate analyses had been conducted. Based on the findings of our review, we make recommendations about reporting of the study design, subcohort definition, numbers of participants, descriptive information and statistical methods, which could be used alongside existing STROBE guidelines for reporting observational studies.

Abstract 54: Procalcitonin, Copeptin and Midregional Pro-atrial Natriuretic Peptide as Markers of Ischemic Stroke Risk: The Northern Manhattan Study

Background: Chronic infections and neuroendocrine dysfunction may be risk factors for ischemic stroke. We hypothesized that selected blood biomarkers of infection (procalcitonin, or PCT), hypothalamic-pituitary-axis function (copeptin), and hemodynamic stress (midregional pro-atrial natriuretic peptide, or MRproANP) would be associated with incident ischemic stroke risk in the multi-ethnic, urban Northern Manhattan Study (NOMAS) cohort. Methods: A case-cohort study was performed among initially stroke-free participants from the prospective population-based NOMAS study. The mean follow up was 11 years. Cases were defined as first ischemic stroke (including fatal) with available baseline blood (n=172). We randomly selected controls among those who did not develop an event (n=344). Biomarkers were measured in a blinded batch analysis (Laboratory of the Medical University Clinic, Aarau, Switzerland, using B.R.A.H.M.S assays by Thermo Fisher Scientific). We calculated hazard ratios and 95% confidence intervals (HR, 95% CI) using Cox proportional hazards models, with inverse probability weighting to correct for the case-cohort study design, to estimate the association with risk of stroke after adjusting for demographic, behavioral, and medical risk factors. Results: Mean age of cases was 72 (IQR 65-78); 59% were female. After full adjustment, those with PCT in the top quartile, compared to the lowest quartile, were at increased risk of ischemic stroke (adjusted HR 1.98, 95% CI 1.02-3.83). Those with MRproANP levels in the top quartile, compared to the lowest quartile, were also at increased risk of stroke (adjusted HR 3.45, 95% CI 1.58-7.52), but not those with higher copeptin levels. The distribution of MRproANP differed by stroke etiology. Levels of MRproANP were greater for cardioembolic strokes (CE), and MRproANP levels were predictive of CE (adjusted HR 3.29 per SD, 95% CI 1.89-5.72). Conclusion: Higher levels of procalcitonin, a marker of infection, and MRproANP, a marker for hemodynamic stress, were independently associated with ischemic stroke risk in this multiethnic, urban cohort. MRproANP was specifically associated with cardioembolic stroke risk. Further study is needed to confirm these results.

A case-cohort study with propensity score matching to evaluate the effects of mannitol on venous thromboembolism

Mannitol has been shown to damage endothelial cells and activate coagulation pathways leading to intravascular thrombosis. Dehydration and hemagglutination have also been associated with mannitol use, although the risk of clinically evident venous thromboembolism (VTE) disease is not well-defined. The aim of this study was to compare the risk of VTE in critically ill neurological patients who received mannitol compared to only hypertonic saline. A case-cohort study design with propensity score matching was used to evaluate the risk of VTE among patients who received mannitol compared to those who received hypertonic saline alone. The odds of thrombosis were evaluated by the Cochran-Mantel-Haenszel method and conditional logistic regression was used to adjust for year of treatment. Ninety-one of 330 patients (27.6%; 95% confidence interval [CI] 23–33%) developed a VTE; however, the yearly proportion remained unchanged over the 8year study period. Cumulative use of mannitol declined and use of hypertonic saline increased significantly. The odds of thrombosis for those exposed to mannitol compared to hypertonic saline alone was 1.11 (95% CI 0.65–1.73; p=0.75). This remained insignificant after adjusting for year of injury. In conclusion, despite a significant change in the pattern of osmotic therapy used at our institution, the proportion of patients with VTE remained unchanged. We found no evidence that mannitol use was associated with VTE compared to hypertonic saline alone.

Association of Serum Uric Acid and Incident Nonspine Fractures in Elderly Men: The Osteoporotic Fractures in Men (MrOS) Study

Uric acid (UA) is produced from purines by the enzyme xanthine oxidase, and elevated levels may cause arthritis and kidney stones. Conversely, UA also appears to function as an antioxidant and may protect against the oxidative stress associated with aging and disease. We performed a prospective fracture case-cohort study to understand the relation of UA and fracture risk in older men enrolled in the Osteoporotic Fractures in Men (MrOS) study. In the cohort of 5994 men aged 65 years and older attending the baseline MrOS examination, we evaluated a subgroup 1680 men in a case-cohort study design. The analytic group included 387 men with incident nonspine fractures (73 hip) and a random sample of 1383. Serum UA was measured in baseline serum samples. Modified proportional hazards models that account for case-cohort study design were used to estimate the relative hazards (RH) of hip and nonspine fracture in men for serum UA. Models were adjusted for age, race, clinic site, body mass index, vitamin D, parathyroid hormone, walking speed, Physical Activity Scale for the Elderly (PASE) score, frailty, and total. Subjects with incident nonspine fractures were older, had lower total hip bone mineral density (BMD), and higher serum phosphorus. There was an 18% decreased risk of nonspine fractures (95% confidence interval [CI] 0.71-0.93; p = 0.003) per 1 SD increase of baseline serum and 34% decreased risk of nonspine fractures in quartile 4 of UA versus quartiles 1, 2, and 3 (95% CI 0.49-0.89; p = 0.028) compared with nonfracture cases after multivariate adjustment. Hip fractures were not significantly associated with UA. Total hip BMD was significantly higher in the group of men with high UA levels compared with lower UA levels and increased linearly across quartiles of UA after multivariate adjustment (p for trend = 0.002). In summary, higher serum UA levels were associated with a reduction in risk of incident nonspine fractures but not hip fractures and higher hip BMD.

Interim Exposures As Predictors Of Venous Thromboembolism (VTE) Recurrence: A Population-Based, Case-Cohort Study

BackgroundRecurrent VTE is frequent and may be fatal; the 2-week case fatality rate after recurrent pulmonary embolism is 11%. However, predictors of VTE recurrence remain uncertain. ObjectiveTo identify independent predictors of VTE recurrence, including interim exposures, adjusted for baseline characteristics and treatments. MethodsUsing the resources of the Rochester Epidemiology Project, we identified all Olmsted County, MN residents with objectively-diagnosed incident VTE over the 13-year period, 1988-2000. All patients surviving ≥1 day were followed forward in time for first objectively-diagnosed VTE recurrence, death or other loss to follow-up, or 12/31/2005, whichever came first. VTE recurrence was defined as new thrombosis of a previously uninvolved venous territory or re-thrombosis of a previously involved venous territory after interim clearing of the incident thrombosis. We estimated the cumulative incidence of VTE recurrence using the Kaplan Meier product limit method, both overall and by incident cancer-associated, idiopathic and non-cancer secondary VTE. For all patients with VTE recurrence, and a random sample of all patients with incident VTE, we reviewed the complete medical records in the community and collected demographic and baseline characteristics, treatments (heparin and warfarin [including proportion of time in therapeutic range], IVC filter, aspirin, statins) and interim VTE risk factor exposures. Using a case-cohort study design with Barlow's weighting scheme, we tested these demographic, baseline and interim characteristics as potential predictors of VTE recurrence using time-dependent Cox proportional hazards modeling. ResultsAmong 1261 incident VTE patients who survived ≥1 day, 306 developed recurrent VTE over 6,485 person-years of follow-up. The cumulative incidence of VTE recurrence at 30 and 180 days, and 1 and 5 years, were 4.5%, 8.2%, 10.5% and 20.3%, respectively. The five-year cumulative recurrence rates among patients with incident cancer-associated, idiopathic and non-cancer secondary VTE were 42.6%, 26.8% and 18.5%, respectively. Among the random cohort of 415 incident VTE cases, 381 (92%) and 359 (87%) received heparin and warfarin therapy for a median (IQR) 5 (4 - 7) and 119 (63 - 194) days, respectively. From multivariable analysis, interim exposure to trauma, major surgery (general, cardiac or gynecologic), infection, hospitalization for acute medical illness or active cancer after the incident VTE were each associated with an increased hazard of VTE recurrence, while use of warfarin and achievement of a therapeutic APTT within the first day of starting heparin were associated with reduced hazards. Although measures of time in therapeutic range while on heparin or warfarin were associated with a reduced risk of recurrence from univariate analyses, these results were not significant when adjusting for other risk factors. ConclusionsAmong patients with incident VTE, new exposure to trauma, major surgery, infection, hospitalization for acute medical illness or active cancer are independent predictors of VTE recurrence; patients with such exposures should be considered for VTE prophylaxis. Disclosures:No relevant conflicts of interest to declare.

Global DNA methylation and one-carbon metabolism gene polymorphisms and the risk of breast cancer in the Sister Study

Global decrease in DNA methylation is a common feature of cancer and is associated with genomic and chromosomal instability. Retrospective case-control studies have reported that cancer patients have lower global methylation levels in blood DNA than do controls. We used prospectively collected samples and a case-cohort study design to examine global DNA methylation and incident breast cancer in 294 cases and a sample of 646 non-cases in the Sister Study, a study of 50 884 women aged 35-74 years who had not been diagnosed with breast cancer at the time of blood draw. Global methylation in DNA from peripheral blood was assessed by pyrosequencing of the LINE-1 repetitive element. Quartiles of LINE-1 methylation levels were associated with the risk of breast cancer in a dose-dependent fashion (P, trend = 0.002), with an increased risk observed among women in the lowest quartile compared with those in the highest quartile (hazard ratio = 1.75; 95% confidence interval 1.19, 2.59). We also examined 22 polymorphisms in 10 one-carbon metabolism genes in relation to both LINE-1 methylation levels and breast cancer. We found three single-nucleotide polymorphisms in those genes associated with LINE-1 methylation: SLC19A1 (rs1051266); MTRR (rs10380) and MTHFR (rs1537514), one of which was also associated with breast cancer risk: MTHFR (rs1537514). PON1 (rs757158) was associated with breast cancer but not methylation.