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Liver enzymes and risk of all-cause mortality in general populations: a systematic review and meta-analysis.

BACKGROUND
Gamma glutamyltransferase (GGT), alanine aminotransferase (ALT), aspartate aminotransferase (AST) and alkaline phosphatase (ALP), commonly used as markers of liver dysfunction, have been implicated with risk of all-cause mortality. The prospective evidence on the associations in general populations has not been reliably quantified.


METHODS
We conducted a systematic review and meta-analysis of published prospective cohort studies evaluating the associations of baseline levels of these enzymes with all-cause mortality in general populations. Relevant studies were identified in a literature search of MEDLINE, EMBASE and Web of Science up to March 2013. Authors of unpublished studies provided data on request.


RESULTS
Nineteen unique cohort studies with aggregate data on over 9.24 million participants and 242 953 all-cause mortality outcomes were included. In a comparison of extreme thirds of baseline GGT and ALP levels, relative risks (RRs) (95% confidence intervals) for all-cause mortality were 1.60 (1.42-1.80) and 1.38 (1.17-1.63), respectively. The corresponding RRs for ALT were 0.82 (0.78-0.86) and 1.43 (1.08-1.90) in North American and Asian populations, respectively. There was no strong evidence of an association of AST with all-cause mortality: RR 1.23 (0.80-1.88). The pooled RRs per 5 U/l increment in GGT and ALP levels were 1.07 (1.04-1.10) and 1.03 (1.01-1.06), respectively.


CONCLUSIONS
Available data indicate positive independent associations of baseline levels of GGT and ALP with all-cause mortality, consistent with linear dose-response relationships. There were geographical variations in the association of ALT with all-cause mortality which require further investigation. The potential incremental prognostic values of GGT and ALP in mortality risk assessment need evaluation.