1.Blood biochemistry BA will have obvious abnormalities in blood biochemistry due to liver injury caused by severe intrahepatic cholestasis, mainly manifested as abnormal liver function index and bilirubin index. The analysis of postnatal blood biochemical indexes can help to diagnose BA. By comparing the blood biochemical indexes of children with BA and neonatal hepatitis (NH), it was found that when the ratio of blood biochemistry GGT/AST exceeded 2, children with BA were more likely to have BA, with a sensitivity of 80.9% and specificity of 72.2% for GGT/AST over 2. The sensitivity of GGT>250U/L in the diagnosis of BA was 83.3%, specificity 70.6% and negative The sensitivity, specificity and positive likelihood ratio of GGT>150U/L in the diagnosis of BA was 91.7%, 88% and 7.8 for children aged less than 4 weeks, especially when the GGT level was correlated with age. Ultrasound is a rapid, noninvasive test, and is a widely used, simple and easy-to-use test especially for screening and diagnosis of pediatric biliary atresia. The triangular cord sign (TC), changes in gallbladder volume, appearance and systolic function, changes in liver size and texture, and even changes in hepatic artery diameter are considered ultrasound indications for the presence of BA, with the TC sign found at the hilar being the most sensitive. The abnormalities of the gallbladder on ultrasound in BA are mainly the absence of the gallbladder, the absence of the gallbladder lumen, and the length of the gallbladder less than 1.5 cm. The abnormalities of the gallbladder contraction are mainly the low or no contraction of the gallbladder after eating, with 77% accuracy, 85% sensitivity and 73% specificity. In addition, because BA is usually associated with liver fibrosis, hepatomegaly and heterogeneous echogenicity are seen on liver ultrasound in BA, and the degree of hepatomegaly and heterogeneous echogenicity does not correlate with age, but with the degree of liver fibrosis. In conclusion, the TC sign is a direct and specific objective criterion for the diagnosis of BA, but it is not the only criterion. Gallbladder changes and liver size and texture changes are also important reference indications for the diagnosis of BA. 3.Liver biopsy Among the various auxiliary examinations, liver aspiration biopsy is an invasive diagnostic method. However, the North American Society for Pediatric Gastroenterology, Hepatology and Nutrition (NASPGHAN) advocates that puncture liver biopsy should be used as a diagnostic test when the diagnosis of cholestasis in infants cannot be confirmed. Liver biopsy is an important test to differentiate BA from infantile idiopathic hepatitis, with an accuracy of 100%, its specificity of 95.7% and sensitivity of 100% for the diagnosis of BA. The pathological features of infantile idiopathic hepatitis are mainly hepatocyte destruction, while BA mainly presents with biliary system changes, such as hepatobiliary hyperplasia, bile duct and intrahepatobiliary protein embolism, and hilar fibrosis, of which hepatobiliary hyperplasia is the most important indication to distinguish BA from infantile idiopathic hepatitis. In the early stages, infantile idiopathic hepatitis and BA are very similar in terms of clinical presentation and blood biochemistry, so liver biopsy is a reliable test to distinguish between them with an accuracy of 96.9%. In addition, 17.9% of BA liver biopsies reveal bile duct plate development malformations. 4.Cholangiography Cholangiography is currently the standard test for definite BA diagnosis because it can clearly show the structure of the bile duct. This test can be performed laparoscopically or through open surgery. Since open surgery can be used for this test, Kasai surgery can be performed once the diagnosis is clear, so many hospitals use open surgery for this test. However, with the popularization and development of minimally invasive techniques, laparoscopic-assisted cholangiography is gradually gaining popularity among pediatric surgeons. The advantages of laparoscopic-assisted cholangiography are that it is simple, precise, safe and minimally invasive, and it avoids unnecessary surgery in children with a non-BA diagnosis on imaging. With the popularization of the laparoscopic Kasai procedure, laparoscopic-assisted cholangiography is becoming an increasingly common method to confirm the diagnosis of BA. By comparing the consistency of other BA diagnostic methods with laparoscopic-assisted cholangiography, we found that liver biopsy was 91.7%, ultrasound was 81.7%, hepatobiliary nuclide imaging was 75%, and MRCP was 73%, which shows that cholangiography is the gold standard for the diagnosis of BA. In conclusion, cholangiography is the gold standard for definitive diagnosis of BA, and laparoscopy with its minimally invasive and precise nature makes laparoscopy-assisted cholangiography a widely popular diagnostic method. To improve the chance of preoperative diagnosis of BA, ultrasound as a noninvasive and widely available diagnostic technique is particularly important in improving the diagnostic rate of BA, but it is influenced by ultrasound equipment and personnel quality, and the accuracy of ultrasound diagnosis of BA has been improving in recent years with the updating of equipment and improvement of personnel quality. Liver biopsy is an important test for differentiating idiopathic hepatitis from BA in infants, with an accuracy of more than 80%. For children with persistent jaundice after birth and suspected cholestasis, ultrasound should be used first. If TC signs are found under ultrasound, the initial diagnosis of BA can be made, and the child should be transferred to a hospital where BA surgery can be performed for further cholangiography to clarify the diagnosis and surgical treatment; if no TC signs are seen under ultrasound, liver aspiration biopsy can be performed to improve the diagnosis of BA, and if the diagnosis still cannot be made, cholangiography is feasible to confirm the diagnosis. Parents can contact me by phone if they have any questions about the examination.