Liver injury is frequently encountered in pediatric clinical practice. Because there is a large reserve of liver function and many liver diseases often do not show clinical signs until they have progressed to an advanced stage, laboratory tests to determine the presence and type of liver injury are important in the treatment and management of liver disease in children. For example, viral hepatitis without jaundice, certain cirrhosis (e.g., Wilson’s disease), and hepatotoxicity of medications can be asymptomatic. Worldwide, hepatophilic virus infection is the most common cause of liver injury and serology as well as nucleic acid testing techniques are usually required to detect the presence of hepatophilic virus and to monitor treatment response. While the incidence of acute viral hepatitis has decreased significantly over the past decade due to the use of hepatitis A and B vaccines and blood screening for hepatitis C virus (HCV), many other causes of liver injury, particularly congenital or acquired metabolic defects and autoimmune disorders, are on the rise. Laboratory tests are particularly critical for confirming these etiologies, especially in patients without evidence of viral infection. Of course, the use of certain medications can also cause liver injury, and clinical information is the most reliable in such cases to determine the likely cause of liver injury.
Because the liver is a complex organ with interrelated metabolic, secretory, and defensive functions, no single or simple laboratory test can cover the entire spectrum of liver function, and therefore there is a wide range of tests for liver function. However, too many tests often impose a heavy financial burden on patients and waste limited medical resources, and sometimes the information obtained from multiple tests often overlaps, so it is especially important to choose the tests and interpret their significance in a rational manner. The purpose of this article is to review with our colleagues the theoretical knowledge about the correct selection and interpretation of relevant indicators in pediatric patients.
I. Laboratory indicators of liver function and injury
We often use laboratory tests to diagnose and detect liver disease as well as to determine the prognosis of liver disease. In some cases, the type of laboratory abnormality helps in the diagnosis, for example, liver function tests can reveal whether the damage is predominantly hepatocellular, or depressed bile or biliary tract obstruction; some liver function indicators, especially when followed up in series, can reflect the degree of liver function damage and thus provide prognostic information. Also laboratory indicators change over time and help to follow the course of liver disease and the patient’s response to treatment. However although we refer to these tests as liver function tests, most of the tests used routinely do not truly reflect liver function. Many tests are an indirect response to liver injury and can be abnormal in many other situations and are not specific.
Tests to evaluate liver disease can be divided into six categories: (1) biochemical activity tests, also called enzymatic tests, which are divided into tests reflecting hepatocyte injury (e.g., ALT, AST, LDH, etc.) and depressed bile tests (GGT, AP, bilirubin (total, conjugated, unconjugated, d), urobilinogen, blood and urinary bile acids, etc.); (2) tests reflecting hepatic synthetic function are albumin and other serum proteins, the prothrombin time and other coagulation indicators, NH3, plasma and urinary amino acids, lipids and lipoproteins, cholesterol and triglycerides, etc.; (3) quantitative functional tests; (4) imaging studies; (5) histology; (6) specific serum tests such as a1at, copper blue protein, AFP, autoantibodies, pathogenic indicators, etc. Some contents have been introduced in special chapters, and here we mainly introduce some common enzymatic tests, synthetic function indicators and specific serological indicators.
1.Biochemical activity test (enzymatic examination)
(1) Indicators of hepatocyte damage
Aminotransferases are most commonly used. Aspartate aminotransferase (AST, SGOT) and alanine aminotransferase (ALT, SGPT) are sensitive markers of liver injury and hepatocyte necrosis. AST is present in the liver, heart muscle, skeletal muscle, kidney, pancreas, and red blood cells. AST levels are elevated in any cause (trauma, ischemia, drugs, etc.) that causes damage to the above tissues. Since this test is non-specific, special care must be taken when diagnosing liver disease based on elevated AST alone. Rhabdomyolysis caused by viral infection and specimen hemolysis can increase AST significantly (with a mild increase in ALT). Cases have been reported and encountered in our clinical practice where significant AST and/or ALT elevations were initially diagnosed as liver disease, but later found to be normal with chronic subclinical myopathy. At this point, examination of LDH isoenzymes can help distinguish between hemolysis or myopathy, or inosine phosphokinase (CPK) or aldolase can help distinguish whether it comes from muscle.
ALT is mainly present in the hepatocyte plasma, and the enzyme activity in the liver is 100 times higher than in the serum; as long as 1% of the hepatocytes are necrotic, the enzyme activity in the serum can be increased by a factor of 1. It is significantly lower in other tissues such as muscle, and therefore has a high specificity for liver disease. ALT and AST normal values vary with age, so it is desirable to have normal values for different ages and different genders. For convenience, we often use 25 U/L as the upper limit of normal for ALT in children in clinical practice.
Some non-hepatic factors can affect the value of transaminase assay and should be noted in clinical practice. Because both AST and ALT use vitamin B6 as a coenzyme, they are measured significantly lower in vitamin B6 deficiency (especially ALT). Uremia can also cause a pseudo-lowering of AST. The reference range for AST is slightly higher in men, obese, and non-whites.
Changes in aminotransferases are of limited use in inferring etiology. the magnitude of increase in AST is often less than that of ALT, with the exception of AST/ALT >2 in 90% of cases in alcoholic liver injury. In addition, AST/ALT is often >1 when chronic hepatitis progresses to cirrhosis.
AST/ALT has been less studied in children, however, it has been reported that in infants with liver disease at 13-month follow-up, the AST/ALT ratio was elevated in cases with poor prognosis and decreased in cases with good prognosis.
Although elevated AST and ALT may be the earliest laboratory evidence of liver disease (e.g., before the appearance of viral hepatitis jaundice) or the only evidence (e.g., in the absence of jaundice), it is important to keep in mind that AST and ALT can be normal even in severe liver disease. Examples include cases of cirrhosis and cases of fulminant hepatitis in static post-necrotic inflammatory disease.
The detection of serum transaminases is of great value in detecting hepatocellular damage and monitoring the clinical course, but is of limited value in making a specific etiological diagnosis. However, some particularly high levels (up to 200 times normal) are seen in acute viral hepatitis, drug hepatotoxicity and ischemia. The degree of elevation is not related to clinical prognosis, nor to the extent of hepatocellular necrosis on liver biopsy, and therefore has no prognostic value.
However, trends in transaminase changes are of value in determining prognosis. Rapidly decreasing transaminase levels but elevated bilirubin, especially with prolonged PT, may indicate submassive hepatic necrosis and poor prognosis. An Austrian study found that patients with gluten enteropathy often had elevated transaminases, which returned to normal with a gluten-free diet.
(2) Experimental indicators of depression bile
These include AP, GGT, 5′-NT, and bilirubin and bile acid tests. Serum alkaline phosphatase (AP) comes from the liver, bone and placenta in pregnancy, and its value is elevated in certain tumors (e.g., bronchopulmonary cancer). In childhood, which is age-dependent due to bone growth, its increase is often difficult to distinguish whether it is caused by liver disease or bone disease, so its use in children is somewhat limited.
Gamma-glutamyl transpeptidase (GGT), also known as gamma-glutamyltransferase, is an enzyme that transfers gamma-glutamyl groups from one peptide chain to another or to L-amino acids. This enzyme is widely distributed in the body and its elevation does not necessarily indicate liver disease.
GGT activity may be inhibited by female hormones, which interfere with the release of GGT from hepatocytes. In addition, the presence of hyperbilirubinemia may also reduce GGT values measured in vitro.
Neonatal GGT levels can be very high, up to 5-8 times the upper limit of normal adults. Preterm infants have higher GGT levels in the first few days than full-term infants. Adult levels are reached at approximately 6-9 months of age. Changes later in older children are shown in the graph on the right. GGT is a very useful indicator when biliary tract disease is suspected.
Compared to other serologic indicators, GGT is among the most sensitive indicators of hepatobiliary disease. Because GGT can be elevated in up to 90% of primary liver diseases, the differential diagnosis is not of great value. The highest levels of GGT are seen in biliary obstruction, but particularly high levels of GGT are also seen in intrahepatic biliary disease, such as Alagille’s syndrome.
GGT levels are associated with the prognosis of idiopathic infantile hepatitis syndrome. The prognosis of infants with normal GGT is poor. It is now clear that some of these cases are due to defects in bile salt synthesis and some are familial depressed bile syndromes. Two major types of progressive familial intrahepatic biliary depression syndrome (PFIC) have been identified in which blood GGT is not elevated. pFIC-1 and 2 have a predominantly neonatal onset with normal or essentially normal blood GGT and cholesterol, elevated serum bile acid concentrations, severe scratchiness, and no histologic bile duct hyperplasia. The extrahepatic factors affecting GGT are listed in the table above. Unlike alkaline phosphatase, serum levels are not elevated in children with bone disease or active bone growth. Also, because medications are used less frequently in childhood, and even when they are used they often have a clear medical history, and children are less likely to drink alcohol, the factors affecting GGT are significantly less in children than in adults, and are more relevant than AP in detecting hepatobiliary systemic disease in children.
The causes of hyperbilirubinemia include increased bilirubin production, decreased uptake and/or binding by the liver, or decreased bile secretion. Increased bilirubin production (e.g., hemolysis) or impaired uptake or binding by the liver (e.g., Gilbert’s disease) causes an increase in serum unconjugated bilirubin (or free bilirubin) levels. Decreased bile production and secretion (e.g., cholecystitis) increases serum conjugated bilirubin and even bilirubin appears in the urine.
Serum bilirubin may not be a particularly sensitive indicator of liver disease or its prognosis, but it is still a necessary test. Normally, total bilirubin is quantified at <1 mg/L (17.1 μmol/L). Total bilirubin must be separated from the direct response component when there is an isolated increase in bilirubin (other routine liver function tests are normal) or in neonatal jaundice. It is important to note that in infancy, when liver function is in the process of maturation, the secretion of conjugated bilirubin from hepatocytes into the bile ducts is not well developed and the excretion of bilirubin forms the rate-limiting step of its metabolism. Therefore, elevated serum bilirubin in infant hepatitis patients is mainly direct bilirubin elevation, which is similar to obstructive jaundice; while some prehepatic factors such as hemolysis that cause increased bilirubin production can also be manifested as a biphasic reaction. Some hospitals can now measure d bilirubin, and there is a relationship between its changes and prognosis, but the data are still scarce and it is not necessary to use it as a clinical routine.
Urine bilirubin (negative when normal) can be detected at the bedside using commercialized urine test strips, which indicate hepatobiliary disease. Unconjugated bilirubin is closely associated with plasma albumin and does not pass through the glomerulus, so even high plasma levels of urine bilirubin are negative, while a positive urine bilirubin indicates elevated plasma conjugated bilirubin (direct response bilirubin). Bilirubinuria can be an early sign of hepatobiliary disease and can occur in acute viral hepatitis even before the onset of jaundice. Because of the poor concentration of urine in infants, normal urine should be colorless, and yellow urine indicates the presence of hepatobiliary disease; black urine is rarely present. In other cases, however, urine bilirubin may be negative despite elevated plasma bilirubin. This may be related to the presence of ascorbic acid (from vitamin C in food) or nitrates (from urinary sepsis) when the bilirubin is oxidized and the urine is falsely negative for bilirubin.
Urinary bilirubin normally occurs in trace amounts (10 mg/L i.e. 17 μmol/L) and can also be detected with commercially available test strips. This intestinal metabolite of bile pigment can be elevated by hemolysis (exceeding the amount of pigment synthesized) or by moderate impairment of hepatic uptake and secretion (i.e., the amount of the pigment in the enterohepatic circulation exceeds the ability of the liver to clear and excrete it). When the biliary tract is completely obstructed, the ability of bilirubin to be secreted into the small intestine for reduction to urobilinogen is extremely low and urobilinogen deficiency may occur. However, urobilinogen is influenced by extrahepatic factors such as renal function, urinary PH, intestinal flora and diarrhea, causing its specificity to be too poor and difficult to interpret the results, so it is not very meaningful in clinical practice.
Blood bile acid testing has been proposed as a sensitive indicator for detecting liver disease in adults, but its use in pediatric patients with liver disease has been questioned. The interpretation of elevated bile acids in neonates and early infants with liver disease is complicated by the presence of physiologic depressed bile that elevates their baseline levels. Attempts to use blood bile acid levels to differentiate biliary atresia from other nonobstructive neonatal depressed bile have also failed. Similarly, in patients with a1at deficiency, blood bile acid testing is of no value in determining prognosis.
New techniques are now available for the fine analysis of multiple precursors and derivatives of bile acids in body fluids to detect birth defects in bile acid metabolism. Screening is first performed using rapid atom bombardment mass spectrometry, and abnormal cases are then finely analyzed using the expensive and time-consuming GC/MS (gas chromatography-mass spectrometry) technique. A number of birth defects have been detected with this method, but only currently can be performed only in some large liver centers abroad.
2.Liver synthesis function detection
Serum proteins, most of the proteins in serum are synthesized in the liver, such as alpha and beta globulins, albumin and coagulation factors. Serum albumin is the main determinant of plasma colloid osmotic pressure, 28-44 g/L in newborns, 37-50 g/L at adult levels at 1 week of age, rising to 45-54 g/L by 6 years of age and maintaining this concentration into adulthood, then declining to typical adult levels. There is no significant difference between males and females. Albumin is synthesized only in the rough endoplasmic reticulum of hepatocytes. The normal liver synthesizes 150 mg/kg per day and it has a biological half-life of approximately 19-21 days. It is a carrier of many substances (e.g. unconjugated bilirubin).
Significant lesions of the liver parenchyma can affect the synthesis of albumin thus reducing the serum albumin level, therefore serum albumin concentration is the main indicator of the residual synthetic function of the damaged liver. Because of its long half-life, a decrease in albumin is often seen as a sign of chronic liver disease rather than acute liver disease. However, compensated chronic liver disease may show a sudden decrease in serum albumin concentration due to acute disease such as sepsis or simply mild disease. In the presence of ascites, the decrease in serum albumin may be primarily due to an expanded volume of distribution. Other non-hepatic causes including malnutrition or loss via the kidneys (nephrotic syndrome), intestines (protein-losing gastrointestinal disease) and skin (burns, etc.) can also lead to hypoproteinemia. A decrease in plasma albumin in liver disease can also be due to an increased rate of degradation, the detailed mechanism of which is unclear.
Serum globulin is usually obtained by subtracting albumin from total protein. It can be further divided by electrophoresis into a1, a2, b and g fractions. a1 fraction, consisting mainly of α1 -antitrypsin (which is absent in A1AT deficiency), copper cyanidin (reduced in Wilson disease) and mucin (an a1 acidic glycoprotein), are acute phase proteins that are elevated in liver disease and many other inflammatory diseases, resulting in a pseudo-normal or Elevated values …… Binding bead protein makes up the majority of a2 and is also part of the acute phase response substances. Transferrin and b-lipoprotein comprise mainly the b fraction. g fraction is mainly immunoglobulin and is synthesized by plasma cells in the reticuloendothelial system.
Patients with a variety of liver diseases may exhibit abnormal plasma protein electrophoresis. Many diseases that do not primarily involve the liver can also have hypoalbuminemia and/or hyperglobulinemia. Therefore, the specific diagnostic value of protein electrophoresis is limited. However, there are exceptions: serum globulins are elevated in chronic liver disease including cirrhosis of any cause, especially in chronic active hepatitis (especially in various autoimmune liver diseases). Typically, polyclonal (broadband) γ-globulin is increased in the presence of reduced albumin. Acute viral hepatitis can also be associated with an acute increase in serum γ-globulin, which usually returns to normal within a few weeks. a1 antitrypsin deficiency can be associated with a1 fraction deficiency, and intravascular hemolysis can cause a2 reduction. Recently it has been clarified that cold globulinemia can be present in the presence of hepatitis C.
Coagulation
The liver plays a three-fold role in the coagulation mechanism: (1) all coagulation factors except factor VIII are partially or fully synthesized by the liver; (2) production and degradation of factors involved in the fibrinolytic process such as fibrinogen and fibrinogen activator; and (3) removal of activated coagulation factors from the circulation. The synthesis of coagulation factors II, VII, IX and X requires the participation of vitamin K and is referred to as a vitamin K-dependent factor. Due to limited hepatic vitamin K stores, in liver disease with depressed bile, vitamin K absorption is impaired, quickly causing vitamin K deficiency and causing clotting disorders.
Commonly used indicators are prothrombin time (PT) and partial thromboplastin time (APTT). PT involves the interaction of fibrinogen (I), prothrombin (II), V, VII and factor X synthesized by the liver and is insensitive to any individual coagulation factor deficiency until it falls below 10% of normal with significant prolongation of PT; APTT involves more coagulation factors, including factors IX and VIII, but not factor VII. PT can be expressed in absolute time (seconds) or as a ratio to normal controls, called INR. after excluding vitamin K deficiency (after 1 mg/year of slow intramuscular or intravenous infusion for at least 4-6hr), coagulation tests are appropriate indicators of hepatic synthetic function.
Because several coagulation factors have a very short plasma half-life (e.g., factor VII is only 3-5hrs), PT can be a timely indicator of changes in hepatic synthetic function, as can occur in acute liver failure, and is a good indicator of prognosis. It has also been suggested that measurement of individual coagulation factors can help determine the prognosis of acute liver failure, with factor VII levels above 8% indicating survival, and vice versa, indicating death. The presence of prolonged PT in chronic liver disease is also indicative of poor prognosis and, together with reduced serum albumin, is the most important indicator in determining preparation for liver transplantation. PT prolongation can be present in any advanced liver parenchymal disease. In some neonatal inherited metabolic diseases, a significant prolongation of PT can occur, which is disproportionate to other indicators of liver malfunction.
In addition to vitamin K deficiency, it should be noted that patients with liver disease may also present with prolonged PT or APTT due to other extrahepatic factors, such as coagulation factor depletion due to DIC. Since factor VIII is synthesized outside the liver, if there is no depletion of coagulation factors, the level of factor VIII is normal or elevated in various liver diseases, so it can be used as an indicator to distinguish whether severe liver disease is combined with DIC. Chronic and fulminant liver disease increases the chance of co-infection and increases the risk of DIC. certain drugs and congenital coagulation factor deficiency also affect PT.
Fibrinogen is synthesized both intra- and extrahepatically, and although its breakdown may be increased, its levels are mostly normal in liver disease. In patients with liver disease, DIC is accompanied by a depletion of other coagulation factors and a decrease in fibrinogen levels. Because it is an acute phase protein, it can be elevated in liver disease. It is often elevated in depressed biliary liver disease.
Almost all of the above information is from adults. Studies of coagulation in full-term or preterm infants and young children have lagged significantly. Differences in their coagulation factor concentrations, ability to produce thrombin, and ability to inhibit thrombin once it is formed have recently been noted. In term or preterm neonates, many coagulation factors, including vitamin K-dependent factors, are present at less than 70% of adult levels. It is now understood that the coagulation system of the neonate is changing and quickly reaches adult levels. Therefore, when evaluating liver function in young infants based on PT, it is important to use normal values appropriate for the gestational age and postnatal age of the young infant (table at left). Despite the prolonged PT and APTT, there is no clinical evidence of an increased risk of bleeding in healthy infants.
Blood ammonia: Ammonia is an amino acid metabolite that is cleared primarily through the urea cycle. In liver disease, elevated blood ammonia is a classic manifestation of liver failure. Defects in enzymes in the urea cycle, Reye’s syndrome, and acute and chronic hepatic encephalopathy are associated with significantly elevated blood ammonia. Arterial blood should be taken for ammonia measurements because only arterial ammonia levels correlate with liver function. To properly measure ammonia, plasma must be separated in a timely manner (<15 min) to prevent false elevations. The extrahepatic factors affecting blood ammonia are shown in the table.
3.Specific serological indicators
(1) Hepatitis markers
Of particular relevance to viral hepatitis are viral antigens and viral antibodies. The most reliable method for diagnosing acute HAV infection is the detection of IgM-anti-HAV, and total anti-HAV antibodies reflect the immune status against hepatitis A virus.
In areas of high prevalence, EIA testing for anti-HCV is sufficient to diagnose previous or current infection with HCV, and HCV-RNA testing is required to determine whether the infection is active. Specimens used for HCV-RNA testing are better in EDTA plasma or timely isolation of serum specimens to avoid false negatives. HDV infection occurs on the basis of HBV infection and the accepted test is for total anti-HDV, which usually disappears 1-5 years after viral clearance. Epidemiological history and clinical manifestations are important for the diagnosis of HEV infection. The EIA test for anti-HEV has poor specificity and a high false-positive rate and is for information only.
Although the national test for hepatitis B and C marker reagents is strict, domestic reagents are still more likely to have test errors because they are mostly used manually. Some people have used different domestic reagents and imported reagents for comparison, the rate of HBsAg and anti-HBs in hepatitis B two-and-a-half is good, anti-HBc is okay, while the rate of HbeAg and anti-HBe is only 50-70%. Therefore, the test should be repeated when there is doubt about the test results. Repeat testing should be done when the following test results occur: HBsAg positive/anti-HBc negative; HBsAg, anti-HBs and anti-HBc positive; anti-HBc positive alone; anti-HBs positive alone in unvaccinated individuals; HBsAg negative and HBeAg positive; HBeAg and anti-HBe positive; total anti-HBc negative and anti-HBc IgM positive.
In addition, special attention should be paid to the following issues.
a. HBsAg false positives: poor serum separation or heparin anticoagulation often leads to HBsAg false positives.
b. HBsAg false negatives: 5% of acutely infected patients remain negative after the onset of hepatitis symptoms, when anti-HBc-IgM and HBV-DNA need to be tested. s gene mutation. Some chronic low-level carriers (occult HBV infection) or latent HBV infection.
c. Simultaneous detection of anti-HBs and HBsAg: transient presence in acute HBV infection with low concentrations of both, and later blood collection and testing for anti-HBs only; before, after or simultaneous infection with different subtypes of HBV, HBsAg can be transient or long-term, and both can also coexist at high titers for a long time; HBV S gene mutation, seen in breakthrough infection after vaccine immunization or chronic HBV infection vaccine After treatment. Anti-HBs false positives.
d. Anti-HBc: critical positives are generally false positives; anti-HBc negatives and HBSAg positives are rare and generally occur in immunodeficiency cases when there are other indicators of HBV replication, such as HBeAg and/or HBV-DNA positivity. Positive anti-HBc alone should be double-reviewed, and after excluding false positives, early recovery from acute infection (window phase, when anti-HBc-IgM is also positive), distant infection with disappearance of anti-HBs, distant infection with low levels of HBsAg (occult HBV infection), or HDV/HCV overlap infection resulting in less HBsAg production should be considered.
e. Mother-to-child transmission of viral infection indicators: HBsAg cannot pass through the placenta, but trace amounts of maternal blood can enter the fetus during delivery, which can cause very low titers of HBsAg positivity, and the presence of high and low levels of HBsAg indicates that intrauterine infection has occurred. HbeAg can pass through the placenta, but the titer is significantly lower than that of the mother and often disappears by 4 months of age. Anti-HBs, anti-HBe, and anti-HBc can all pass freely through the placenta. Maternally transmitted anti-HBs is protective of the infant, and anti-HBe often disappears within 1 year of age. anti-HBc can remain positive until 18 months after birth and disappears by 2 years of age. Anti-HCV antibodies can also be transmitted from mother to child, and the vast majority disappear by 18 months of age. Therefore, a positive anti-HBc or anti-HCV test after 18 months of age mostly indicates active infection or previous infection.
(2) Autoantibody testing related to autoimmune liver disease
The incidence of autoimmune liver disease is also on the rise, and cases have been reported both at home and abroad in recent years. Autoimmune hepatitis (AIH) often has an insidious onset, but can also have an acute onset and be seen in children with acute hepatitis or even liver failure. Laboratory tests are characterized by significant gammaglobulin elevation, positive circulating autoantibodies, and histologic interface hepatitis. Based on the nature of autoantibodies, autoimmune hepatitis is divided into two main types: type 1 manifests as positive anti-smooth muscle antibodies or anti-nuclear antibodies, and type 2 is characterized by positive anti-liver and kidney microsomal antibodies or anti-hepatocyte lysate type 1 antibodies. Overseas, 40% of type 1 and 80% of type 2 autoimmune hepatitis cases are diagnosed in childhood; therefore, autoimmune hepatitis is mainly a pediatric disease. Our hospital has developed an indirect immunofluorescence method to detect relevant autoantibodies. The commonly used antibodies are.
Antinuclear antibodies The potency of ANA antibodies in AIH serum is usually 1:320, and only 16% of patients have a potency of 1:40, but 87% of them are accompanied by positive SMA. This result indicates that ANA is more meaningful for diagnosis when its potency is above 1:80. The fluorescence type of ANA is of little significance for prognostic evaluation.
Anti-smooth muscle antibodies (SMA) are the basic marker of type I AIH and are usually present together with ANA, but in about 26% of cases SMA is the only immunoserological marker. In patients with viral hepatitis, SMA and ANA are rarely present together, so the presence of both is more relevant for the diagnosis of AIH.
Anti-liver and kidney microsomal antibodies (LKM1) are a class of antibodies directed against microsomal antigens. This antibody is the marker antibody for type II AIH and its target antigen is cytochrome monooxygenase P450IID6.
Anti-soluble liver antigen antibody (SLA) This antibody is only seen in AIH patients, so SLA is considered to be the hallmark of AIH. This type of AIH often has some of the features of type I AIH, but patients have negative serum ANA, LKM1 antibodies and antithyroid antibodies, while positive for SMA, antihepatocyte cytoplasm 1 antibodies and anti-mitochondrial antibodies. It is thought that this type of AIH is only a special form of type I AIH and not an independent subtype.
Anti-hepatocyte cytoplasm 1 (LC1) antibodies are only seen in non-HCV-infected patients, and this antibody has previously been used to identify the presence of HCV infection in patients positive for anti-LKM1 antibodies. The rate of anti-LC1 positivity in anti-LKM1-positive patients without HCV infection is 32%, so this antibody should be used as a complementary marker for AIH. In addition about 14% of AIH patients, this antibody is the only positive marker.
Anti-mitochondrial antibody (AMA) is the marker antibody for primary biliary cirrhosis (PBC). Almost 100% of patients with PBC are positive for AMA and have high antibody potency. The target antigen of AMA is pyruvate dehydrogenase E2, and there is no difference in the target antigen recognized by AMA in the sera of AIH and PBC patients. It is noteworthy that AIH patients with positive serum AMA are more effective for glucocorticoid treatment. Mitochondrial antibodies have a direct antagonistic effect on antigens of the mitochondrial lining of several tissues. m2 antigens are most associated with primary biliary cirrhosis, being positive in more than 95% of patients with primary biliary cirrhosis. These multiphase antibodies are also present in 30% of autoimmune chronic active hepatitis and in some drug-induced hepatitis and connective tissue diseases. The antibodies are negative in mechanical biliary obstruction and primary sclerosing cholangitis.
Selection of laboratory indicators in children with liver disease
When liver disease is known or suspected, a group of tests should be performed including at least ALT/AST, TB/DB, ALP/GGT, TP/Alb, ALT more than 10 times the upper limit of normal and ALP less than 3 times the upper limit of normal can diagnose acute liver injury. Checking DB is used to exclude jaundice caused by hemolysis, etc. However, it should be noted that since the infant’s liver is in the process of development, bilirubin excretion from the liver is the rate-limiting step of its bilirubin metabolism, and jaundice caused by prehepatic factors can also manifest as elevated conjugated bilirubin. In viral hepatitis, TB>257umol/L (15mg/dl) or PT exceeding the upper limit of normal by 4s indicates severe liver injury if no other factors are involved. In acetaminophen poisoning, PT prolongation lasting more than 4 days after administration suggests severe liver injury.
Liver disease in children has its own peculiarities, with infectious and metabolic being particularly important. Therefore, tests that should be performed in all stages of liver disease in children include: blood glucose, INR/APTT, complete blood count & smear & reticulocytes, liver and kidney function (ALT/TB/DB/AKP/GGT/Ca/P/Cr/BuN), lipids, HIV antibodies, VitA&E, urine electrolytes and osmolality. blood and urine culture and drug sensitivity, liver and spleen ultrasound, etc. In addition to this, different ancillary tests are needed as the manifestations of liver disease are different at different times and different etiologies need to be considered. In children older than 6 months of age with chronic liver disease or/and hepatomegaly, infectious, metabolic and autoimmune factors should be considered, therefore hepatitis B antigen, hepatitis C antibody, CMV/EBV serology, Ig/C3/C4/autoantibodies, VMA/HVA/AFP, urate/CK, NH3/amino acids, Cu/Zn/coplanin, penicillamine provocation test, eye KF ring and youth ring, skeletal examination, liver biopsy; for acute liver failure should also check blood glucose test (once in 4hr), toxicity screening (especially paracetamol), HAV-IgM/HBc-IgM/anti-HBc/HCV-RNA, fibrinogen, autoantibodies and immunoglobulins, NH3, CK/amylase, AFP, CMV/EBV/HSV/adenovirus microvirus serology, blood gas analysis/lactate/pyruvate, 24-hour urine copper and penicillamine provocation test, urine organic acids, ophthalmologic examination and liver biopsy; infantile hepatitis is currently one of the most common types of liver disease in pediatric clinics, with intrauterine or perinatal infections and endocrine metabolic abnormalities being the most common, so for liver disease in children under 6 months of age, we refer to infantile hepatitis syndrome in cases.