Approach to Liver Chemistries

First of all - even the terminology is confusing. The American College of Gastroenterology now recommends using the terminology 'liver chemistries'. Historically, 'liver enzymes' referred to serum levels of ALT, AST, ALP (and GGT) while 'liver function tests' referred to PT/INR, conjugated (direct) bilirubin, albumin.

Liver enzymes abnormalities are typically the first indication of mild or chronic pathology. Clinical manifestations and abnormalities in PT/direct bili/albumin usually only occur in the context of acute or well-established disease.

Liver enzymes can be listed from most specific to least specific:

- ALT (hepatocytes only)

- AST (hepatocytes AND skeletal/cardiac muscle)

- ALP (hepatocytes lining bile canaliculi AND bone, placenta, GI tract)

- GGT can be used to confirm ALP elevations are specific to bile canaliculi disruption, however, it is even less specific than ALP so there is no clinical utility in ordering it without an established ALP elevation.

Building on this, there are 2 (ish) basic patterns of liver chemistries to recognize:

1.) Hepatotoxic*

- AST, ALT elevation predominate

(1a) Alcoholic liver disease

- AST:ALT > 2

(1b) Non-alcoholic liver disease

- AST:ALT < 1

2.) Obstructive

- ALP, direct bili elevations predominate

*Should ALT/AST >1000 or there be abnormalities in PT/INR, direct bilirubin, albumin consider acute/severe disease

-TJ-

Reference:

Kwo PY, Cohen SM, Lim JK. ACG Clinical Guideline: Evaluation of Abnormal Liver Chemistries. Am J Gastroenterol. 2017 Jan;112(1):18-35. doi: 10.1038/ajg.2016.517. Epub 2016 Dec 20. PMID: 27995906.