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Liver blood tests are typically the first of a series of steps a
physician takes to detect, evaluate and monitor the presence of liver
disease or the extent of liver damage in a client. The jargon used to
describe these tests includes liver panel, hepatic function test and
liver function test (LFT). Since many people with early to moderate
liver disease experience few, if any, symptoms, routine blood testing
is often the first indication of a problem.
Liver blood tests typically consist of six separate tests run on a single blood sample. The tests comprise:
1. Alanine aminotransferase (ALT)
2. Aspartate aminotransferase (AST)
3. Alkaline phosphatase (ALP)
4. Bilirubin
5. Albumin
6. Total protein (TP)
Some additional tests that may be included in a liver panel are:
1. Gamma-glutamyl transferase (GGT)
2. Prothrombin time (PT)
While a guide to understanding the liver panel follows, it is
important to understand only qualified medical practitioner can make a
reliable diagnosis. Because liver disease can still be present despite
blood tests reflecting normal results, liver function tests alone are
insufficient for liver disease diagnosis. Since any test is only an
indication of what is occurring at the exact time of the test,
individual test results are not completely accurate. It is common
practice to administer a liver panel on separate dates, especially if
any results register outside the normal range.
Alanine aminotransferase (ALT)
ALT is an enzyme produced in liver cells. As liver cells are
damaged, ALT leaks into the bloodstream. All types of hepatitis (viral,
alcoholic, drug-induced, etc.) cause liver cell damage that can lead to
ALT elevations. The ALT level is also increased in cases of liver cell
death resulting from other causes, such as shock or drug toxicity.
While the level of ALT typically correlates with the degree of cell
death or inflammation, only liver biopsy (or its equivalent) can
accurately estimate the level of liver inflammation or cell death.
Since the amount of ALT in the bloodstream is a direct quantitative
measurement, this test cannot predict liver damage or disease
progression. The normal ALT level range is between 5 and 60 IU/L
(International Units per Liter).
Aspartate aminotransferase (AST)
AST is a mitochondrial enzyme that is present in the liver, heart,
muscle, kidney and brain. In many cases of liver inflammation, the ALT
and AST levels are elevated roughly in a 1:1 ratio. While AST is often
viewed in comparison to ALT, a high AST level in the bloodstream may be
a sign of liver trouble. The normal range for AST levels in the
bloodstream is between 5 and 43 IU/L.
Alkaline phosphatase (ALP)
In addition to being present in many body tissues (intestines,
kidneys, placenta, bones), ALP is a family of related enzymes produced
in the bile ducts and sinusoidal membranes of the liver. A blockage in
the bile duct will result in an elevation in ALP levels. In addition to
cirrhosis and liver cancer, conditions such as primary biliary
cirrhosis and sclerosing cholangitis will generally show a raised ALP.
Abnormally high ALP can have many causes other than liver damage,
including bone disease, congestive heart failure and hyperthyroidism. A
rise in ALP levels can indicate liver trouble if GGT levels are also
elevated. The normal range of ALP is between 30 and 115 IU/L.
Bilirubin
Bilirubin is a yellow fluid produced in the liver by the break down
of worn-out red blood cells. It is removed from the blood by the liver
in a chemical modification process called conjugation. It is then
secreted into the bile then passed and partially reabsorbed into the
intestines. Elevated bilirubin is caused either by an increase in its
production, a decrease in its uptake by the liver, a decrease in
conjugation, a decrease in its secretion from the liver or a blockage
of the bile ducts.
Many diseases, including those of the liver, can cause elevated
bilirubin levels. Bilirubin can leak from the liver into the
bloodstream if the liver is damaged. When bilirubin builds up, it can
cause jaundice - a yellowing of the eyes and skin, dark urine and light
colored feces. The causes of abnormal bilirubin levels include:
- Viral hepatitis
- Blocked bile ducts
- Other liver diseases
- Liver cirrhosis
Total bilirubin testing measures the amount of bilirubin in the
bloodstream. Normal total bilirubin levels range from .20 to 1.50 mg/dl
(milligrams per deciliter). Direct bilirubin testing measures bilirubin
made in the liver. Normal levels of direct bilirubin range from .00 to
.03 mg/dl.
Albumin
Albumin is the primary protein made by the liver. While albumin is
not the only protein synthesized by the liver, it is the most easily,
reliably and inexpensively measured. Low albumin levels indicate the
liver is not making protein and therefore, not functioning properly.
Albumin levels are typically normal in chronic liver diseases until
cirrhosis and/or liver damage is severe enough to inhibit protein
production. Albumin levels can also be low in conditions such as
malnutrition, some kidney diseases and other, more rare conditions.
Albumin maintains the volume of blood in the veins and arteries. When
albumin levels become very low, fluid can leak from blood vessels into
nearby tissues, causing swelling in the feet and ankles. The normal
albumin range is from 3.9 to 5.0 g/dl (grams/deciliter).
Total Protein (TP)
A total protein blood test measures albumin and all other proteins
in blood, including antibodies that help fight off infection. Many
different things can cause abnormally high or low protein levels. In
addition to liver disease diagnosis, TP can help identify kidney
disease, blood cancer, malnutrition or abnormal body swelling. Normal
protein levels in the bloodstream range from 6.5 to 8.2 g/dl.
Gamma-glutamyl transpeptidase (GGT)
GGT is an enzyme produced in the liver and other tissues. It is
often elevated in those who use alcohol or other toxic substances to
excess. Elevations in GGT, along with elevations in ALP, suggest bile
duct disease. Since the measurement of GGT is extremely sensitive, it
may be elevated in those without liver disease. Raised GGT can often be
seen in cases of fatty liver and where the patient consumes large
amounts of the artificial sweetener, Aspartame. Obesity, primary
biliary cirrhosis, heavy drinking, fatty liver, and certain medications
or herbs that are toxic to the liver can cause GGT levels to rise
beyond the normal range of 5 to 80 IU/L.
Prothrombin time (PT)
A PT test measures how much time it takes for a person’s blood to
clot. Many factors necessary for blood clotting are made in the liver.
When liver function is severely hampered, blood clotting factor
synthesis and its secretion into the blood is diminished. A person with
an abnormally long PT may be at risk for excessive bleeding. A longer
PT can be caused by serious liver disease or:
- A lack of vitamin K
- Blood-thinning medicines
- Other medications that can interfere with the test
- Certain bleeding disorders
The normal time needed for blood to clot is between 10 and 15 seconds.
While not sufficient for diagnosis or evaluation, a basic
understanding of these liver panel components will take some of the
mystery out of your liver panel lab results.
Editor’s Note: Normal blood test results are ranges, and such ranges can differ between medical institutions.
by Nicole Cutler, L.Ac.
References:
www.atdn.org, Liver Function Tests, AIDS Treatment Data Network, 2002.
www.cumc.columbia.edu, Common Laboratory Tests in Liver Diseases, Howard J. Worman, MD, Howard J. Worman MD, 1998.
www.liverdoctor.com, Liver Test, SCB Inc., 2006.
www.liverfoundation.org, Liver Function Tests Factsheet, The American Liver Foundation, 2006.
www.medicinenet.com, Liver Blood Enzymes, MedicineNet
http://www.liversupport.com/wordpress/2006/11/take-the-mystery-out-of-your-liver-tests/
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