'Minor' liver function test abnormalities
Last revised in August 2005
Biochemical tests of 'liver function' are used to investigate a wide range of symptoms and for various purposes in asymptomatic people. This raises the potential to discover significant disease at an early stage in its natural history, but also produces abnormal results in apparently healthy individuals. This is particularly so in the "statin prescribing" era.
The usual "liver function tests" include two separate type of test. Serum albumin and bilirubin provide a true measure of hepatic function, although both can be abnormal for a number of non-hepatic causes. The remaining tests are liver enzyme levels, usually alanine aminotransferase (ALT) or aspartate transaminase (AST) in combination with alkaline phosphatase (ALP) +/- gamma glutamyl transpeptidase (GGT).
The purpose of these answers is to attempt to allow the user to identify situations in which values of one or more of these tests outside of the 95% population reference range (Mean +/- 2 standard deviations for the population) may indicate the presence of clinically significant disease.
In view the statistical phenomenon of regression to mean
[Bland and Altman, 1994], the principle of interval retesting to establish one-off from stable and progressive increases appears sound. There is guidance, but limited evidence, on retesting intervals, although in the asymptomatic context and in view of the slow time course of the potential underlying diseases, the retesting interval of months rather than weeks appears reasonable in the context of 'minor' elevations, commonly described as up to 3-5 times the upper limit of 'normal'. (ULN). Indications for further investigation of persistent rises commonly refer to 1.5 ULN. The limitations of reference ranges are further compounded for liver tests by the fact that population results are not normally distributed and exhibit a right skew effect.
GMS contract indicator: none