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Liver
function tests (LFTs) are commonly used term for medical
tests to show how the liver is doing. People often think
that ALT and AST are the LFTs. As a matter of fact, the
Liver has so many functions, and there are more than 700
different laboratory tests that have been developed for
them. New tests are still coming to reflect newer
functions discovered.
The existing
LFTs can be roughly classified into four categories:
1. Tests
that reflect liver cell damages: It consists of the
levels of serum enzymes and serum iron. Serum enzymes,
such as Alanine aminotransferase (ALT), Aspartate
aminotransferase (AST), Alkaline phosphatase (AKP),
Gamma-glutamyl-transpeptidase (GGT), show the liver cell
leakage and necrosis. Among them, ALT and AST are the
more sensitive indicator for liver damage. ALT in
particular is much more sensitive in reflecting the
acute liver damage relative to AST's ability reflect the
degree of damage. The reasoning being ALT is more
specific to the liver. During the recovery stage of the
acute hepatitis, if ALT is normalized, but GGT is still
elevated, this usually means the hepatitis is turning to
chronic. In Chronic hepatitis, if GGT is consistently
elevated, this usually indicates that the liver
inflammation is active.
2. Tests
that reflect metabolic and secretary functions of the
liver: These tests are used to test the metabolic and
eliminative functions of the liver. Some internal and
external metabolites and chemicals have to be absorbed
and metabolized and eliminated by the liver, such as
bile, bile acid, drugs. Clinically, Bilirubin total and
direct is the commonly used to show this function. When
there is bile retention, or bile metabolic disorder, the
patient may have jaundice, dark urine, pale stool,
yellowish eye and skin. If bilirubin levels continuously
rise while ALT is decreased, this separation of the
levels of enzyme and bilirubin may suggest the disease
is worsening.
3. Tests
that reflect synthetic and storage functions of the
liver: Serum albumin and blood clotting factors are
synthesized in the liver. Glycogen is synthesized and
stored in the liver to regulate the blood sugar levels.
Serum albumin level drop down means the protein
synthesis function deteriorated. Prolonged
PT(Prothrombin time, is a test to see how quickly the
blood is able to form a clot.) PTT (Partial
thromboplastin time also called as activated partial
thomboplastin time. It is a test to show the ability of
the blood to form a clot.) If the GTT tests showed the
blood sugar regulatory function of the liver are
deteriorating, it may also show that the liver's
glycogen synthesis function are also deteriorated and
patient may experience hypoglycemia or high blood sugar
levels.
4. Tests
that reflect fibrostic activities: g-globulin increases
show that the phagositosis function of Kuffer cells are
deteriorating. This shows that the Kupffer calls can't
clear the antigens from the blood circulation and
nutrients absorbed from the intestine. Serum hyaluronic
acid (HA), procollagen type III (PCIII), collagen IV (CIV)
and laminin (LN) can reflect the activities of
fibroblasts, fat storage cells, and stellate cells.
These cells activities have a close relationship to
fibrosis progression. Although we have so many different
liver function tests, usually only the liver profile is
regularly tested. Non-routine tests are usually very
expensive. When we read the test results, we should not
just look at only one or two items to judge the liver
condition. Rather, we should look at all the figures and
look for trends. Results from one test are not enough to
make a solid determination of anything since many
factors can cause abnormal fluctuations in the body. |
