How to check bile acid

In clinical practice, bile acid testing is often necessary when examining liver function. This is because the production and metabolism of bile acids are closely related to the function of the human liver. In general, the level of bile acid can be used to determine the extent of liver damage in a person. So how is bile acid tested clinically? What should we pay attention to when checking bile acid?

Total bile acid test

The production and metabolism of bile acids are closely related to the liver. Serum bile acid levels are an important indicator of liver parenchymal damage. The determination of serum total bile acid (TBA) is of great value in the diagnosis of liver disease.

Name

Total bile acid test

Category

Biochemical examination

Table of contents

1.1 Normal value

2.2 Clinical significance

3.3 Notes

Normal value

Fasting, adult serum 1-7μmol/L (3.5±1.75).

Clinical significance

(1) Acute hepatitis: In acute hepatitis, serum TBA increases significantly, reaching 10-100 times the normal level, or even higher. Yang Changguo et al. reported that the fasting TBA (F-TBA) level of 60 healthy controls was 4.9±2.4 μmol/L, and the serum TBA (P-TBA) level 2 hours after lunch was 8.2±2.9 μmol/L; in 34 cases of acute hepatitis in the acute phase, the F-TBA level was 124.1±74.0 μmol/L, and the P-TBA level was 152.2±73.0 μmol/L, which were 13 times and 11 times the upper limit of normal, respectively, and the abnormal rate was 100%. In patients who have just recovered from acute hepatitis, serum TBA drops from the initial high value to normal levels almost at the same time as AST. If it continues to not drop or even increases, it may develop into a chronic disease. A follow-up study of 21 patients with acute hepatitis found that among those whose TBA recovered to below 10 μmol/L, no cases of chronic progression were found one year later. However, among those whose TBA increased and AST dropped to normal, 4 out of 5 cases developed chronic hepatitis. (2) Chronic hepatitis: Foreign studies suggest that in patients with chronic hepatitis, if the TBA level exceeds 20 μmol/L, chronic active hepatitis may be considered. Yang Changguo et al. in China reported that the p-TBA and F-TBA of chronic persistent hepatitis were 23.6±12.5μmol/L and 7.7±4.6μmol/L, respectively, while those of chronic active hepatitis were 111.3±45.1μmol/L and 78.7±38.9μmol/L, respectively. The F-TBA and P-TBA of chronic active hepatitis were significantly higher than those of chronic persistent hepatitis. Therefore, serum TBA determination is of great significance for the identification of chronic hepatitis and for monitoring the prognosis and treatment effect of chronic active hepatitis. (3) Cirrhosis: In cirrhosis, the liver's ability to metabolize bile acids decreases, and serum TBA increases at different stages of cirrhosis. The increase is generally higher than that in chronic active hepatitis, even in the late stages of cirrhosis. When liver disease activity is reduced to the lowest level, indicators such as bilirubin, transaminase and alkaline phosphatase return to normal, but serum TBA still remains at a high level. (4) Alcoholic liver disease: Serum TBA may increase in patients with alcoholic liver disease. When severe liver damage occurs in alcoholic liver disease (including cirrhosis), serum TBA increases significantly, while the increase is not obvious in mild or moderate damage. Some people have also reported that the reliability and sensitivity of serum TBA determination in diagnosing hepatocellular damage in alcoholic liver disease are far superior to various enzymatic tests and galactose tolerance tests. It is even recommended to use serum TBA plus β-hexosaminidase as a diagnostic indicator for alcoholic liver disease. Sumino et al. reported that 60 minutes after patients with alcoholic liver disease ingested egg yolk, serum TBA increased significantly, and they believed that the 60-minute postprandial TBA measurement was more meaningful for the diagnosis of alcoholic liver disease. (5) Toxic liver disease: Serum TBA determination is better than routine liver function tests for the diagnosis of toxic liver disease. It has been reported that among 23 workers exposed to styrene, 11 had elevated serum TBA levels, while only 3 had abnormalities in other indicators. It also has diagnostic significance for acute liver damage caused by liver poisoning due to taking certain therapeutic drugs in clinical practice. (6) Cholestasis: Serum TBA determination has high sensitivity and specificity for the diagnosis of cholestasis. Extrahepatic bile duct obstruction and intrahepatic cholestasis including acute hepatitis, early biliary cirrhosis, neonatal cholestasis, and pregnancy cholestasis can all cause increased TBA. In the early stages of bile duct obstruction, bile secretion decreases, causing a significant increase in serum TBA, which remains almost unchanged at different stages of obstruction; while serum bilirubin levels vary with different stages. The bile acid content in the liver tissue of patients with cholestasis is significantly higher than that of normal people, with CA increasing by 8 times, CDCA increasing by 4 times, and DCA increasing by only 1.5%. After extrahepatic obstruction is relieved by drainage, serum TBA levels drop rapidly, while other indicators slowly return to normal. In all liver diseases, the postprandial serum TBA level and abnormal rate are higher than those in the fasting state, so the postprandial TBA measurement is more sensitive than the fasting measurement for the diagnosis of liver disease. It has been reported that the diagnostic sensitivity and specificity of postprandial TBA for various liver diseases is as high as 100%, while 40% of patients with fasting serum TBA are within the normal range. Whether acute hepatitis turns into chronic hepatitis, continuous monitoring of postprandial TBA levels can observe the chronic process. Whether chronic active hepatitis develops liver fibrosis changes, continuous post-meal monitoring can also help understand the fibrosis process and determine the extent of liver damage without a liver biopsy.

Precautions

(1) LD in serum can also reduce NAD+ to NADH in the presence of its substrate (serum contains a certain amount of lactic acid), resulting in a high blank value. In this method, sodium pyruvate is added to inhibit LD activity and can effectively reduce blank absorbance. (2) The concentrations of the components in the reaction mixture are: 3α-HSD 5U/L diaphorase 500U/L NAD+ 1mmol/L NTB 0.2g/L pH 7.50 (3) The absorbance of the reaction mixture is affected by protein, so the sodium glycocholate standard solution is prepared in mixed serum. The original bile acid and other substances that may participate in the reaction in the mixed serum need to be eliminated using a P tube. (4) 3α-HSD products contain dithiothreitol (DTT). Excessive use of the enzyme preparation may affect the reduction of NTB. (5) The linearity of this method is up to 250 μmol/L. If serum bile acid exceeds this value, appropriate dilution should be made. (6) Noigen ET-180 is a nonionic surfactant with the chemical name polyoxy-ethyleneolylether, produced by Dai-ichi Ko-gyo Seiyaku Co., Ltd. in Kyoto, Japan. It can prevent precipitation when added to the reaction mixture, has no effect on the activity of 3α-HSD and diaphorase, and does not affect the sensitivity of this assay system. (7) The TBA content in serum is low, and the specimen contains a large amount of interfering substances, the most important of which is lactate dehydrogenase (LDH). LDH can affect the reduction reaction of NAD+. The amount of NADH generated by LDH is often much larger than that generated by the reaction catalyzed by 3α-HSD with the participation of TBA. Since all types of hepatitis can cause elevated serum LDH, the influence of LDH must be eliminated during the determination. Methods include: heating the serum at 67°C for 30 minutes, adding oxalic acid as a blocking agent for LDH, alkali or acid treatment, or using sodium pyruvate to inhibit LDH activity, among which the sodium pyruvate method is the best. The interference of other reducing substances can be eliminated by setting up a double reagent. The sample is first incubated with a system without 3α-HSD to allow the interfering substances in the sample to react. Then 3α-HSD is added to allow TBA to react, thereby eliminating the interference.

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