Liver tests are common blood tests used to determine if the liver is functioning normally. The blood samples for the liver tests are drawn from a vein and sent to a laboratory for analysis. The results are typically used together, not individually, to diagnose potential issues with the liver. So, one number being slightly raised will not typically trigger a major examination of the liver. If various values indicate a problem, a liver biopsy (or CT/MRI) may be necessary next step to confirm and further analyze the test results.
The most common biomarkers of the test are:
- Aspartate aminotransferase (AST)
- Alanine aminotransferase (ALT)
- Alkaline phosphatase (ALP)
Each of these has results given to them in numbers. The laboratory provides a ‘normal value’ or ‘reference value’ to the test, which shows you whether your test is within the normal range. Abnormal functions are shown by how much they are below or above the normal range.
Routine Liver Blood Tests
- As many medications and prescriptions are known to cause liver damage, these lab tests are often part of routine monitoring for patients that are taking such medications.
- Drinking alcohol is also known to cause liver damage, if the amount of alcohol is excessive and the drinking occurs over an extended period of time.
What are the normal liver enzyme levels?
AST (Aspartate Phosphatase) Lab Results
This test is typically used to detect a liver injury or an active or chronic liver problem. The heart can also release AST, so it is important to look at the entire set of liver tests, rather than just this one test.
AST levels can be dramatically affected by shock, low blood pressure or any other condition that deprives the liver of blood and oxygen.
Normal Level: 10 – 34 U/L
ALT (Alanine Aminotransferase) Lab Results
This test is used to detect liver injuries and long-term liver disease. Highly elevated levels may indicate active hepatitis from any cause, including virus, alcohol, drug or toxin. Some prescription and over-the-counter medications can cause an increase in ALT levels.
ALT levels can be dramatically affected by shock, low blood pressure or any other condition that deprives the liver of blood and oxygen. For this reason, we can expect the sickest patients to have elevations in ALT, especially those who are being cared for in an intensive care area.
Normal level: 7 – 55 U/L
ALP (Alk Phos, Alkaline Phosphatase) Lab Results
ALP is a substance found in the bile ducts of the liver. Damage or obstruction of the bile ducts may result in elevated levels of ALP. That means an elevation in Alkaline Phosphatase does’t necessarily mean that the liver itself is having the problem, but the ducts that leave the liver may be the issue.
Normal Level: 44 – 126 U/L
Total Bilirubin (T. Bili) Lab Results
This lab test measures the total amount of bilirubin in the blood, including direct and indirect bilirubin. Bilirubin is produced during the normal process of blood cells dying and the liver excretes bilirubin through bile. Too much bilirubin in the blood results in the patient looking yellow, or jaundiced. This test may detect elevated levels of bilirubin before jaundice is present.
Normal Level: 0.1 – 1.23 mg/dL
Indirect Bilirubin (I. Bili) Lab Results
Indirect bilirubin does not dissolve in water. In order to dissolve in water, and be eliminated from the body, it must go to the liver where it is made into direct (water soluble) bilirubin.
Indirect Bilirubin = Total Bilirubin – Direct Bilirubin
Normal Level: 0.2 – 0.9 mg/dL
Direct Bilirubin (D. Bili) Lab Results
Direct bilirubin has been converted into a water soluble form of bilirubin by the liver. The proportion of indirect bilirubin to direct bilirubin may change if the liver has difficulty converting indirect into direct.
Normal Level: 0 – 0.3 mg/dL
Albumin Lab Results
Albumin is a protein made by the liver that is very common in blood plasma, which can be measured in the blood. If the liver has chronic or acute damage, the level of albumin in the blood will typically be low. A low level of albumin can also be caused by poor nutrition, and is often seen in patients who are not eating well on a regular basis. It can also be seen in patients who are chronically ill.
Normal Level: 3.4 – 5 g/dL
Causes of elevated Liver Enzymes:
- Nonalcoholic Fatty Liver Disease (NAFLD)
- Alcoholic Liver Disease (ALD)
- Medication-Associated Liver Injury
- Viral Hepatitis
- Alpha-1 antitrypsin Deficiency
- Wilson Disease
- Cytomegalovirus (CMV)
- Autoimmune Hepatitis
What are early signs of liver damage?
Early signs of liver disease often include general gastrointestinal complaints that commonly are associated with many other conditions. In some cases, early liver disease symptoms are not noticeable.
- Abdominal pain (located on the right side of the body, beneath the ribs)
- Abnormal stools
- Flu-like symptoms (e.g., fatigue, nausea, vomiting, muscle or joint pain, fever)
- Loss of appetite
- Swelling of abdomen and/or legs
Symptoms that are more specific to liver problems include the following:
- Bleeding and bruising more easily
- Dark urine
- Jaundie (i.e., yellowing of skin/eyes)
- Sensitivity to medications (e.g., experiencing stronger side effects)
Liver disease may cause toxins that are normally filtered out of the blood by the liver to accumulate in the brain, leading to the following symptoms:
- Difficulty concentrating
- Memory loss
- Mental confusion
- Sleep disturbances
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