***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: Serum biochemical liver tests ( LTs ) ( ALT , AST , GGT ) and platelet counts are often used to screen for chronic liver disease . Population ‐based data on abnormal LTs in Mediterranean areas are lacking . The prevalence and etiology of abnormal LTs were assessed from 2002 to 2003 in a 1 in 5 systematic r and om sample of the general population who were 12 years of age or older in Cittanova , a southern Italian town with 10,600 inhabitants .  LTs , indices of metabolism , and markers of HBV and HCV infection  were assayed and  alcohol intake was recorded in the selected population . In virus‐free individuals with abnormal LTs , LTs were retested , and  upper abdominal echography  and tests for other causes of liver damage were undertaken . Among the 1,645 individuals screened , the prevalence of anti‐HCV was 6.5 % ; the prevalence was particularly high in individuals over 50 years of age . The corresponding prevalence for HBsAg was 0.8 % . The overall prevalence of individuals with abnormal LTs was 12.7 % ( 95 % CI : 11.1‐14.3 ) . The probable cause of abnormal LTs was excessive alcohol in 45.6 % , HCV in 18.6 % , HBV in 1 % , alcohol plus HCV and /or HBV in 8.8 % , and rare diseases in 2 % . In 24 % of individuals with abnormal LTs , the probable cause was nonalcoholic fatty liver disease ( NAFLD ) ; in this subgroup , increased body weight , hypercholesterolemia , and hyperglycemia were common , and 63.3 % of them had a bright liver at echography . In conclusion , in southern Italy , a Mediterranean area where dietary habits are different from those in industrialized areas , one eighth of the general population has abnormal LTs suggestive of possible liver damage ; NAFLD appears to be emerging as a potentially important etiology of this presumed liver injury . ( HEPATOLOGY 2005;41:1151–1159 . BACKGROUND & AIMS Elevated serum alanine aminotransferase ( ALT ) and gamma-glutamyltransferase ( GGT ) activities are markers of liver injury , but may also be associated with other diseases and death . In a prospect i ve , national , population -based sample , we examined whether elevated ALT and GGT were associated with increased risk of all-cause and disease-specific mortality . METHODS Death certificate-based 12-year mortality was analyzed among 14,950 adult participants in the third US National Health and Nutrition Examination Survey , 1988 - 1994 , who were negative for markers of viral hepatitis B and C. Abnormal ALT was defined as > 30 U/L in men or > 19 U/L in women , and abnormal GGT as > 51 U/L in men or > 33 U/L in women . RESULTS Cumulative mortality was 13.9 % from all causes , including 4.2 % from cardiovascular disease , 4.2 % from neoplasms , 0.44 % from diabetes , and 0.13 % from liver disease . In multivariate-adjusted analyses , elevated ALT was not associated with all-cause mortality ( hazard ratio [ HR ] , 1.2 ; 95 % confidence interval [ CI ] , 0.88 - 1.6 ) . ALT elevation was associated with deaths from liver disease ( HR , 8.2 ; 95 % CI , 2.1 - 31.9 ) , but not from cardiovascular disease ( HR , 0.90 ; 95 % CI , 0.56 - 1.4 ) , neoplasms ( HR , 1.0 ; 95 % CI , 0.65 - 1.5 ) , or diabetes ( HR , 2.4 ; 95 % CI , 0.65 - 9.1 ) . All-cause mortality increased with elevated GGT ( HR , 1.5 ; 95 % CI , 1.2 - 1.8 ) , as did mortality from liver disease ( HR , 13.0 ; 95 % CI , 2.4 - 71.5 ) , neoplasms ( HR , 1.5 ; 95 % CI , 1.01 - 2.2 ) , and diabetes ( HR , 3.3 ; 95 % CI , 1.4 - 7.6 ) , but not from cardiovascular disease ( HR , 1.3 ; 95 % CI , 0.80 - 2.0 ) . CONCLUSIONS In the US population , elevated GGT was associated with mortality from all causes , liver disease , cancer , and diabetes , while ALT was associated only with liver disease mortality Abstract Objective To examine the relation between the normal range of serum aminotransferase concentration and mortality from liver disease . Design Prospect i ve cohort study . Setting Korea Medical Insurance Corporation study with eight years ' follow up . Participants 94 533 men and 47 522 women aged 35 - 59 years . Main outcome measure Mortality from liver diseases according to death certificate . Results There was a positive association between the aminotransferase concentration , even within normal range ( 35 - 40 IU/l ) , and mortality from liver disease . Compared with the concentration < 20 IU/l , the adjusted relative risks for an aspartate aminotransferase concentration of 20 - 29 IU/l and 30 - 39 IU/l were 2.5 ( 95 % confidence interval 2.0 to 3.0 ) and 8.0 ( 6.6 to 9.8 ) in men and 3.3 ( 1.7 to 6.4 ) and 18.2 ( 8.1 to 40.4 ) in women , respectively , The corresponding risks for alanine aminotransferase were 2.9 ( 2.4 to 3.5 ) and 9.5 ( 7.9 to 11.5 ) in men and 3.8 ( 1.9 to 7.7 ) and 6.6 ( 1.5 to 25.6 ) in women , respectively . According to receiver operating characteristic curves the best cut-off values for the prediction of liver disease in men were 31 IU/l for aspartate aminotransferase and 30 IU/l for alanine aminotransferase . Conclusion People with slightly increased aminotransferase activity , but still within the normal range , should be closely observed and further investigated for liver diseases Background Although serum γ-glutamyltransferase ( GGT ) predicted cardiovascular diseases ( CVD ) in prospect i ve studies and may be useful in risk assessment , prediction in older adults was weaker in several studies . Methods We performed a nested case-control study with 5 - 12-year follow-up in 137 CVD deaths and 249 controls ( frequency-matched on age , sex , and examination year , age range 26 - 85 years ) . Results An age interaction of serum GGT and CVD mortality ( P value for interaction = 0.02 ) was observed . After adjusting for known CVD risk factors , compared with the lowest tertile , odds ratios ( 95 % confidence intervals ) in participants less than 70 years ( half the participants ) were : middle tertile : 2.17 ( 0.68 - 6.97 ) , top tertile up to GGT less than 50 U/I : 3.54 ( 1.07 - 11.7 ) , and GGT ≥ 50 U/l : 4.69 ( 1.16 - 18.9 ) . In participants aged more than or equal to 70 years , GGT was not related to CVD . Well-known demographic and health behavior associations with serum GGT were observed only in controls among participants aged less than 70 years . Conclusion Our findings suggest that serum GGT within its normal range can predict CVD mortality in those aged less than 70 years , but may have limited usefulness for risk assessment in older adults . Eur J Cardiovasc Prev Rehabil 16:16 - 20 © 2009 The European Society of Background — There is evidence from recent studies that γ-glutamyltransferase ( GGT ) is likely to be associated with cardiovascular disease ( CVD ) . However , few studies to date with sufficient sample size and follow-up investigated the association of GGT with CVD mortality . Methods and Results — The relation of GGT to the risk of death from CVD was examined in a cohort of 163 944 Austrian adults that was monitored for up to 17 years . To evaluate GGT as an independent predictor , Cox proportional hazards models were calculated , which adjusted for established risk factors . In both men and women , high GGT was significantly ( P<0.001 ) associated with total mortality from CVD , showing a clear dose-response relationship . Adjusted hazard ratios ( 95 % CI ) per log GGT increase were 1.66 ( 1.40 to 1.98 ) in men and 1.64 ( 1.36 to 1.97 ) in women . In men , subgroup analyses showed that high GGT was positively associated with incident fatal events of chronic forms of coronary heart disease ( P=0.009 ) , congestive heart failure ( P<0.001 ) , and hemorrhagic ( P=0.01 ) and ischemic stroke ( P<0.001 ) . No significant associations were observed for acute myocardial infa rct ion ( P=0.16 ) . In women , hazard ratios suggested associations in all subgroups ; however , for hemorrhagic and ischemic stroke they were not statistically significant ( P=0.09 and P=0.07 , respectively ) . In addition , subgroup analyses stratified by age revealed a stronger relationship of GGT in younger participants . Hazard ratios for total CVD were 2.03 ( 1.53 to 2.69 ) in men and 2.60 ( 1.53 to 4.42 ) in women younger than 60 years . Conclusions — This study demonstrates in a large , prospect ively observed cohort that GGT is independently associated with cardiovascular mortality Context Current upper limits ( 500 nkat/L [ 30 U/L ] for women , 667 nkat/L [ 40 U/L ] for men ) for serum alanine aminotransferase ( ALT ) level were defined in population s that included persons with nonalcoholic fatty liver disease ( NAFLD ) and persons with hepatitis C virus ( HCV ) infection . Contribution This study redefined ALT limits in blood donors at low risk for NAFLD and without hepatitis B or C ( 317 nkat/L [ 19 U/L ] in women , 500 nkat/L [ 30 U/L ] in men ) . When applied to 209 anti-HCV-positive donors , the new thresholds had 76.3 % sensitivity and 88.5 % specificity in identifying patients with hepatitis C viremia compared with 55 % and 97.4 % for old thresholds . Implication s Laboratories should consider revising the upper limits of normal for ALT to improve the sensitivity of this test in identifying sub clinical liver disease . The Editors Serum alanine aminotransferase ( ALT ) concentration is the most commonly used variable for assessment of liver disease ( 1 , 2 ) . However , particularly in the case of chronic hepatitis C virus ( HCV ) infection , ALT measurement often fails to identify patients with minimal to mild necroinflammatory activity ( 3 - 7 ) . Current upper limits of normal for ALT level were set , on average , at 667 nkat/L ( 40 U/L ) ( range , 500 to 833 nkat/L [ 30 to 50 U/L ] ) in studies conducted over the past 10 years ( 1 , 3 - 5 , 7 , 8) . Such thresholds , however , were mostly computed in the 1980s , when ALT testing was introduced as a surrogate marker for the screening of non-A , non-B hepatitis among blood donors and before anti-HCV testing and restrictive behavioral criteria for donor selection were implemented . Furthermore , so-called reference population s were likely to include many persons with nonalcoholic fatty liver disease , now recognized as the most prevalent cause of chronic liver disease in developed countries ( 8 - 10 ) . Current reference ranges for ALT level probably underestimate the frequency of chronic liver disease . Because dietary and behavioral risks for liver disease are widespread in many countries , a critical revision of ALT limits would require the definition of healthy ranges rather than a generic up date of normal ranges . Thus far , several factors have hampered this task . For example , to obtain solid data , many clinical , biochemical , and behavioral variables potentially related to liver disease must be investigated , requiring screening of large numbers of persons . Furthermore , repeated blood donors , who currently represent the vast majority of blood-donation c and i date s , can not be included in the sampling frame , because they have been selected on the basis of ALT activity during the past two decades . We report the results of a 4-year study of first-time blood-donation c and i date s. To up date the definitions of healthy ranges for serum ALT level , we identified a population at low risk for sub clinical liver disease by exploring factors related to enzyme activity in both healthy persons and those with mild abnormalities on liver tests . Next , we tested the sensitivity 
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The ALT-mortality association was inconsistent and seems particularly susceptible to age after synthesizing the previous prospect i ve studies .
In terms of the age , ALT activity was more valuable in predicting mortality in the older population ; extremely low ALT levels indicated a higher all-cause , CV-related , and cancer-related mortality  .
ALT activity may therefore be a useful biomarker when predicting the long-term survival of elderly patients