***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: BACKGROUND Considerable morbidity and mortality are still associated with congestive heart failure ( CHF ) syndromes , despite improvement in therapy . Activation of neurohormonal , inflammatory , and oxidative mechanisms has been shown to contribute to the significant morbidity and mortality . Erythropoietin ( EPO ) is a cytokine known to regulate erythroid proliferation , attenuate apoptosis and oxidative stress , and promote angiogenesis . We prospect ively evaluated the predictive value of baseline EPO , N-terminal pro-B-type natriuretic peptide , and C-reactive protein levels in patients with clinical ly controlled chronic CHF . METHODS One hundred eighty-eight out patients from a CHF clinic had baseline assessment of EPO , N-terminal pro-B-type natriuretic peptide , and C-reactive protein levels and a complete clinical data profile . These patients were followed up for 24 months for any hospitalization due to CHF or mortality . RESULTS Circulating EPO levels were higher in CHF patients and increased in subjects with higher New York Heart Association scores . Levels of EPO ( at a cutoff of 23 mU/mL ) and N-terminal pro-B-type natriuretic peptide ( cutoff at the median of 1556 pg/mL ) were found to be strong predictors of mortality and CHF hospitalization , whereas C-reactive protein levels ( cutoff of 10 mg/L ) predicted CHF hospitalizations but not mortality . Left ventricular ejection fraction was found to be a predictor of mortality but not of CHF hospitalizations . Serum levels of EPO were significantly correlated with N-terminal pro-B-type natriuretic peptide and C-reactive protein levels but not with left ventricular ejection fraction . CONCLUSION If confirmed in large-scale clinical studies , determination of circulating EPO levels may aid in predicting morbidity and mortality in patients with clinical ly controlled congestive CHF Prognosis studies are investigations of future events or the evaluation of associations between risk factors and health outcomes in population s of patients ( 1 ) . The results of such studies improve our underst and ing of the clinical course of a disease and assist clinicians in making informed decisions about how best to manage patients . Prognostic research also informs the design of intervention studies by helping define subgroups of patients who may benefit from a new treatment and by providing necessary information about the natural history of a disorder ( 2 ) . There has recently been a rapid increase in the use of systematic review methods to synthesize the evidence on research questions related to prognosis . It is essential that investigators conducting systematic review s thoroughly appraise the method ologic quality of included studies to be confident that a study 's design , conduct , analysis , and interpretation have adequately reduced the opportunity for bias ( 3 , 4 ) . Caution is warranted , however , because inclusion of method ologically weak studies can threaten the internal validity of a systematic review ( 4 ) . This follows abundant empirical evidence that inadequate attention to biases can cause invalid results and inferences ( 5 - 9 ) . However , there is limited consensus on how to appraise the quality of prognosis studies ( 1 ) . A useful framework to assess bias in such studies follows the basic principles of epidemiologic research ( 10 , 11 ) . We focus on 6 areas of potential bias : study participation , study attrition , prognostic factor measurement , confounding measurement and account , outcome measurement , and analysis . The main objectives of our review of review s are to describe methods used to assess the quality of prognosis studies and to describe how well current practice s assess potential biases . Our secondary objective is to develop recommendations to guide future quality appraisal , both within single studies of prognostic factors and within systematic review s of the evidence . We hope this work facilitates future discussion and research on biases in prognosis studies and systematic review s. Methods Literature Search and Study Selection We identified systematic review s of prognosis studies by search ing MEDLINE ( 1966 to October 2005 ) using the search strategy recommended by McKibbon and colleagues ( 12 ) . This strategy combines broad search terms for systematic review s ( systematic review .mp ; meta- analysis .mp ) and a sensitive search strategy for prognosis studies ( cohort , incidence , mortality , follow-up studies , prognos * , predict * , or course ) . We also search ed the reference lists of included review s and method ologic papers to identify other relevant publications . We restricted our search to English- language publications . One review er conducted the search and selected the studies . Systematic review s , defined as review s of published studies with a comprehensive search and systematic selection , were included if they assessed the method ologic quality of the included studies by using 1 or more explicit criteria . We excluded studies if they were meta-analyses of independent patient data only , if their primary goal was to investigate the effectiveness of an intervention or specific diagnostic or screening tests , or if they included studies that were not done on humans . Data Extraction and Synthesis Individual items included in the quality assessment of the systematic review s were recorded as they were reported in the publication ( that is , the information that would be available to readers and future review ers ) . We review ed journal Web sites and contacted the authors of the systematic review s for additional information when authors made such an offer in their original papers . When review s assessed different study design s by using different sets of quality items , we extracted only those items used to assess cohort studies . We constructed a comprehensive list of distinct items that the review s used to assess the quality of their included studies . The full text of each review was screened . All items used by the review authors to assess the quality of studies were extracted into a computerized spreadsheet by 1 review er . Two experienced review ers , a clinical epidemiologist and an epidemiologist , independently synthesized the quality items extracted from the prognosis review s to determine how well the systematic review s assessed potential biases . We did this in 3 steps : 1 ) identified distinct concepts or domains addressed by the quality items ; 2 ) grouped each extracted quality item into the appropriate domain or domains ; and 3 ) identified the domains necessary to assess potential biases in prognosis studies . We then used this information to assess how well the review s ' quality assessment included items from the domains necessary to assess potential biases . After completing each of the first 3 steps , the review ers met to attempt to reach a consensus . The consensus process involved each review er presenting his or her observations and results , followed by discussion and debate . A third review er was available in cases of persistent disagreement or uncertainty . In the first step , all domains addressed by the quality items were identified . The first review er iteratively and progressively defined the domains as items were extracted from the included review s. The second review er defined domains from a r and om list of all extracted quality items . Limited guidance was provided to the review ers so that their assessment s and definitions of domains would be independent . The review ers agreed on a final set of domains that adequately and completely defined all of the extracted items . In the second step , review ers independently grouped each extracted item into the appropriate domains . Review ers considered each extracted item by asking , What is each particular quality item addressing ? or What are the review 's authors getting at with the particular quality assessment item ? . Items were grouped into the domain or domains that best represented the concepts being addressed . For example , the extracted items at least 80 % of the group originally identified was located for follow-up and follow-up was sufficiently complete or does n't jeopardize validity were each independently classified by both review ers as assessing the domain completeness of follow-up adequate , whereas the extracted item quantification and description of all subjects lost to follow-up was classified as assessing the domain completeness of follow-up described . In the third step , we identified the domains necessary to assess potential biases . Each review er considered the ability of the identified domains to adequately address , at least in part , 1 of the following 6 potential biases : 1 ) study participation , 2 ) study attrition , 3 ) prognostic factor measurement , 4 ) confounding measurement and account , 5 ) outcome measurement , and 6 ) analysis . Domains were considered to adequately address part of the framework if information garnered from that domain would inform the assessment of potential bias . For example , both review ers judged that the identified domain study population represents source population or population of interest assessed potential bias in a prognosis study , whereas the domain research question definition did not , although the latter is an important consideration in assessing the inclusion of studies in a systematic review . Finally , on the basis of our previous ratings , we looked at whether each review included items from the domains necessary to assess the 6 potential biases . We calculated the frequency of systematic review s by assessing each potential bias and the number of review s that adequately assessed bias overall . From this systematic synthesis , we developed recommendations for improving quality appraisal in future systematic review s of prognosis studies . We used Microsoft Access and Excel 2002 ( Microsoft Corp. , Redmond , Washington ) for data management and SAS for Windows , version 9.1 ( SAS Institute , Inc. , Cary , North Carolina ) for descriptive statistics . Role of the Funding Sources The funding sources , the Canadian Institutes of Health Research , the Canadian Chiropractic Research Foundation , the Ontario Chiropractic Association , and the Ontario Ministry of Health and Long Term Care , did not have a role in the collection , analysis , or interpretation of the data or in the decision to su bmi t the manuscript for publication . Results We identified 1384 potentially relevant articles . Figure 1 shows a flow chart of studies that were included and excluded . Figure 2 shows the number of review s identified by year of publication . We excluded 131 systematic review s of prognosis studies that did not seem to include any quality assessment of the included studies ; this represented 44 % of prognosis review s. We included 163 review s of prognosis studies in our analysis ( 13 - 175 ) . The most common topics were cancer ( 15 % ) , musculoskeletal disorders and rheumatology ( 13 % ) , cardiovascular ( 10 % ) , neurology ( 10 % ) , and obstetrics ( 10 % ) . Other review s included a wide range of health and health care topics . Sixty-three percent of the review s investigated the association between a specific prognostic factor and a particular outcome ; the remainder investigated multiple prognostic factors or models . The number of primary studies included in each systematic review ranged from 3 to 167 ( median , 18 [ interquartile range , 12 to 31 ] ) . A complete description of the included review s is available from the authors on request . Figure 1 . Flow diagram of inclusion and exclusion criteria of systematic review s. Figure 2 . Number of systematic review s of prognosis studies identified over time . Quality Items One hundred fifty-three review s provided adequate detail to allow extraction of quality items . Eight hundred eighty-two distinct quality items were extracted from the review s. Most review s developed their own set of quality items , with only a few applying criteria from previous review s. Most quality items BACKGROUND Worsening renal function ( WRF ) is frequently observed in patients with heart failure and is associated with worse outcome . The aim of this study was to examine the association of the cardiac serum marker N-terminal pro-B-type natriuretic peptide ( NT-pro-BNP ) and WRF . METHODS A total of 125 consecutive patients of a tertiary care outpatient clinic for heart failure prospect ively underwent evaluation of renal function every 6 months . The association of baseline NT-pro-BNP with WRF was analysed during a follow up of 18 months . RESULTS Twenty-eight ( 22.4 % ) patients developed WRF ( increase in serum creatinine ≥0.3 mg/dL ) . Patients with WRF ( 2870 pg/mL , interquartile range ( IQR ) 1063 - 4765 ) had significantly higher baseline NT-pro-BNP values than patients without WRF ( 547 pg/mL , IQR 173 - 1454 ) . The risk for WRF increased by 4.0 ( 95 % CI 2.1 - 7.5 ) for each st and ard deviation of log NT-pro-BNP . In multivariable analysis including age , baseline renal function , ejection fraction , New York Heart Association class and diuretic dose , only NT-pro-BNP and diabetes were independent predictors of WRF . At a cut-off level of 696 pg/mL , NT-pro-BNP showed a sensitivity of 92.9 % and a negative predictive value of 96.4 % for WRF . CONCLUSION NT-pro-BNP is a strong independent predictor of WRF within 18 months in patients with systolic heart failure with a high negative predictive value . Further studies are needed to evaluate reno-protective strategies in patients with elevated NT-pro-BNP OBJECTIVES We investigated whether plasma amino-terminal pro-brain natriuretic peptide ( NT-proBNP ) , a marker of cardiac dysfunction and prognosis measured in CORONA ( Controlled Rosuvastatin Multinational Trial in Heart Failure ) , could be used to identify the severity of heart failure at which statins become ineffective . BACKGROUND Statins reduce cardiovascular morbidity and mortality in many patients with ischemic heart disease but not , overall , those with heart failure . There must be a transition point at which treatment with a statin becomes futile . METHODS In CORONA , patients with heart failure , reduced left ventricular ejection fraction , and ischemic heart disease were r and omly assigned to 10 mg/day rosuvastatin or placebo . The primary composite outcome was cardiovascular death , nonfatal myocardial infa rct ion , or stroke . RESULTS Of 5,011 patients enrolled , NT-proBNP was measured in 3,664 ( 73 % ) . The midtertile included values between 103 pmol/l ( 868 pg/ml ) and 277 pmol/l ( 2,348 pg/ml ) . Log NT-proBNP was the strongest predictor ( per log unit ) of every outcome assessed but was strongest for death from worsening heart failure ( hazard ratio [ HR ] : 
    Output:
    
BNP was positively associated with all-cause and HF mortality .
NT-proBNP was positively associated with all-cause and cardiovascular mortality .
BNP and NT-proBNP levels are useful for estimating prognosis in persons with chronic stable HF .