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• Total Bile Acids (Enzyme Cycling Method) Assay DZ042A
• Background
• Methods
• Bile Acid In Clinical Medicine
• Bile Acids and Heptatitis
• Bile Acids and Pregnancy
• Serum Total Bile Acids Test in Veterinary Clinics
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Bile Acid in Clinical Medicine

Diagnostic Value of Serum Total Bile Acids Test

The liver removes bile acids effectively from the portal circulation because of the presence of bile acid transporters on the sinusoidal membrane of hepatocytes. The high extraction efficiency (first-pass clearance is 75-90%) is the reason for low peripheral blood levels of total bile acids (2-10 μmole/L) compared with portal concentrations of bile acids (60- 80 μmole/L). Any decrease in the extraction efficiency caused by a decrease in the hepatic blood flow and/or due to heaptocellular damage or any compromises of liver function will result in increases of serum levels of total bile acids. Serum or plasma TBA levels is a sensitive indicator of liver function in all species, reflecting both hepatic synthesis, secretion, and re-absorptive functions. Therefore, testing for serum TBA will help to detect liver functional changes before the formation of more advanced clinical signs of illness such as icterus. This early sensitivity is very important in clinical diagnosis because it allows for the possibility of treatment before extensive and irreversible damage is done. Studies in humans with various liver diseases showed that serum TBA can be used to assess hepatic dysfunction with valuable information that is not provided by conventional tests on serum levels of liver enzymes such as ALT and AST. It is important to distinguish between the information provided by liver enzymes (ALT, AST) and TBA. ALT and AST are enzymes released from damaged liver cells and therefore are indicators of hepatocellular integrity. TBA is an indicator of liver function. However, the test will not provide a definitive diagnostics of the primary problem, merely on early confirmation that there is a hepatobiliary deficiency. Therefore, once a patient becomes jaundiced, the benefits of TBA testing decline unless used to monitor response to treatments.

Prevalence of Liver Disease and Screening Tests

The World Health Organization (WHO) estimates there are 12million acute and chronic liver failure patients worldwide. The prevalence of liver disease is particularly high in developing countries, especially in Asia.

Liver disease is a major medical problem in China, where it results in more than 400,000 deaths per year. Hepatitis is the third most prevalent disease in China, and 20 million people have active viral liver disease. Official estimates suggest that China’s yearly medical expenses for liver disease infections are more than $12 billion.

In the United States, the National Center for Health Statistics and the American Liver Foundation estimates that:

• Over 26,000 people die each year from chronic liver Cirrhosis, a chronic liver disease that is the seventh leading disease-related cause of death in the US.
• Approximately 3.5 million people in the US arechronically infected with the hepatitis C virus.
• Between 8,000 and 10,000 people die of hepatitis C annually in the US. By the year 2010, the number ofdeaths from hepatitis C is expected to rise to 38,000 each year.
• There are approximately 22,000 pregnant women who are carriers of hepatitis B each year in the US.
• Each year, 400,000 to 500,000 surgeries to remove the gallbladder are performed in the US.

Early detection of liver disease and liver functionality can help patients get effective therapeutic treatment, prevent disease progress, and save lives.

Liver health screening test panels normally include the following tests:
Liver enzymes: ALT, AST, GGT, AFU, ADA, ChE.
Liver tumor marker: AFP.
Liver function markers: Bilirubin (total and direct), TBA

Among these tests, TBA offers the highest sensitivity for early stage of liver dysfunction. This test as part of the liver test panel has been widely performed in China and other Asian countries for early detection of liver diseases.

Fasting serum TBA determination can be used clinically in the diagnosis and prognosis of liver disease in conjunction with standard liver function tests. Because of the increased sensitivity of TBA determination as compared to standard liver function tests, TBA testing offers significant additional diagnostic information concerning liver function, especially in minor hepatic derangements. It is of particular benefit in the determination of hepatic dysfunction as a result of chemical and environmental injury. Liver injury as a result of occupational or environmental exposure to a wide variety of chemical substances can be determined to a much finer degree by TBA than by standard liver enzymes, especially when the liver has been only slightly damged. Studies showed that 73% of patients exposed to harmful organic solvents had elevated serum TBA levels, whereas increased levels of gamma- glutamyl transpeptidase (g-GT), alanine aminotransfertase (ALT), aspartate aminotransferase (AST) and bilirubin were only 8, 3, 2 and 1%, respectively. Clinical studies have found that standard liver function tests are not sensitive enough to determine hepatic dysfunction caused by organic solvent exposure, whereas serum TBA testing has a much greater specificity and sensitivity in the diagnosis of liver disease induced by chemical and environmental exposure and in diagnosis of low levels of hepatic dysfunction. Other indications for serum TBA testing include patients presenting with generalized pruritis and pregnant women experiencing nausea and vomiting during pregnancy. Both of these conditions can be a result of impaired hepatic function, yet standard liver function tests are usually not sensitive enough to be of value. In contrast, serum TBA determination has shown a significant correlation between hepatic dysfunction and both nausea and vomiting during pregnancy and generalized prurits. Serum TBA testing also offers useful prognostic information in cases of cirrhosis. In one large study, serum TBA concentration correlated more closely with mortality than the commonly used clinical and laboratory parameters such as the Number Connection Test, acites, albumin, pseudocholinesterase, bilirubin, prothrombin time, and nutritional state. Serum TBA testing is generally not suitable for differentiating between the various types of liver diseases.

Conditions with elevated fasting serum total bile acids levels:

• Anicteric liver disease
• Alcoholic liver disease
• Biliary atresia
• Chemical-induced liver injury
• CirrhosisCholestasis
• Cystic fibrosis
• Drug-induced liver injury
• Generalized pruritis
• Hepatoma, primary
• Nausea and vomiting of pregnancy
• Neonatal hepatitis syndrome
• Protracted diarrhea of infancy
• Reye’s syndrome
• Viral hepatitis

Normal Range of Fasting Total Bile Acids in Human Serum

Numerous studies have shown that the normal range of fasting total bile acids levels in human serum is 2-10 μmole/L. Postprandial serum TBA levels are generally higher than fasting serum TBA levels. It has recently been proposed that measurement of both fasting and postprandial serum TBA levels can provide additional value in differential diagnosis of chronic liver dysfunctions, (as seen in Table 4).

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