The symptoms of neonatal hepatitis are similar to another infant liver disease, biliary atresia, in which the bile ducts are destroyed for reasons that are not understood. The infant with biliary atresia is also jaundiced and has an enlarged liver, but is growing well and does not have an enlarged spleen. These symptoms, along with a liver biopsy and blood tests, are needed to distinguish biliary atresia from neonatal hepatitis.

The purpose of screening for viral hepatitis is to identify people infected with the disease as early as possible. This allows for early treatment, which can prevent disease progression, and decreases transmission to others.

A liver biopsy is performed, where a small piece of the liver is taken out of the child with a needle and examined with a microscope. The biopsy will often show that four or five liver cells are combined into a large cell that still functions, but not as well as a normal liver cell. This type of neonatal hepatitis is sometimes called "giant cell hepatitis."

A number of liver function tests (LFTs) are available to test the proper function of the liver. These test for the presence of enzymes in blood that are normally most abundant in liver tissue, metabolites or products. serum proteins, serum albumin, serum globulin,

alanine transaminase, aspartate transaminase, prothrombin time, partial thromboplastin time.

Imaging tests such as transient elastography, ultrasound and magnetic resonance imaging can be used to examine the liver tissue and the bile ducts. Liver biopsy can be performed to examine liver tissue to distinguish between various conditions; tests such as elastography may reduce the need for biopsy in some situations.

The CDC recommends the hepatitis A vaccine for all children beginning at age one, as well as for those who have not been previously immunized and are at high risk for contracting the disease.

For children 12 months of age or older, the vaccination is given as a shot into the muscle in two doses 6–18 months apart and should be started before the age 24 months. The dosing is slightly different for adults depending on the type of the vaccine. If the vaccine is for hepatitis A only, two doses are given 6–18 months apart depending on the manufacturer. If the vaccine is combined hepatitis A and hepatitis B, up to 4 doses may be required.

Chronic liver disease takes several years to develop and the condition may not be recognised unless there is clinical awareness of subtle signs and investigation of abnormal liver function tests.

Testing for chronic liver disease involves blood tests, imaging including ultrasound and a biopsy of the liver. The liver biopsy is a simple procedure done with a fine thin needle under local anaesthesia. The tissue sample is sent to a laboratory where it is examined underneath a microscope.

It is believed that only 5–50% of those infected in the United States and Canada are aware of their status. Testing is recommended for those at high risk, which includes injection drug users, those who have received blood transfusions before 1992, those who have been in jail, those on long term hemodialysis, and those with tattoos. Screening is also recommended in those with elevated liver enzymes, as this is frequently the only sign of chronic hepatitis. Routine screening is not currently recommended in the United States. In 2012, the U.S. Centers for Disease Control and Prevention (CDC) added a recommendation for a single screening test for those born between 1945 and 1965.

Anti-viral medications are available to treat infections such as hepatitis B. Other conditions may be managed by slowing down disease progression, for example:

- By using steroid-based drugs in autoimmune hepatitis.

- Regularly removing a quantity of blood from a vein (venesection) in the iron overload condition, hemochromatosis.

- Wilson’s disease, a condition where copper builds up in the body, can be managed with drugs which bind copper allowing it to be passed from your body in urine.

- In cholestatic liver disease, (where the flow of bile is affected due to cystic fibrosis) a medication called ursodeoxycholic acid (URSO, also referred to as UDCA) may be given.

A1AT deficiency remains undiagnosed in many patients. Patients are usually labeled as having COPD without an underlying cause. It is estimated that about 1% of all COPD patients actually have an A1AT deficiency. Thus, testing should be performed for all patients with COPD, asthma with irreversible airflow obstruction, unexplained liver disease, or necrotizing panniculitis. The initial test performed is serum A1AT level. A low level of A1AT confirms the diagnosis and further assessment with A1AT protein phenotyping and A1AT genotyping should be carried out subsequently. The Alpha-1 Foundation offers free, confidential testing.

As protein electrophoresis does not completely distinguish between A1AT and other minor proteins at the alpha-1 position (agarose gel), antitrypsin can be more directly and specifically measured using a nephelometric or immunoturbidimetric method. Thus, protein electrophoresis is useful for screening and identifying individuals likely to have a deficiency. A1AT is further analyzed by isoelectric focusing (IEF) in the pH range 4.5-5.5, where the protein migrates in a gel according to its isoelectric point or charge in a pH gradient.

Normal A1AT is termed M, as it migrates toward the center of such an IEF gel. Other variants are less functional and are termed A-L and N-Z, dependent on whether they run proximal or distal to the M band. The presence of deviant bands on IEF can signify the presence of alpha-1 antitrypsin deficiency. Since the number of identified mutations has exceeded the number of letters in the alphabet, subscripts have been added to most recent discoveries in this area, as in the Pittsburgh mutation described above. As every person has two copies of the A1AT gene, a heterozygote with two different copies of the gene may have two different bands showing on electrofocusing, although a heterozygote with one null mutant that abolishes expression of the gene will only show one band. In blood test results, the IEF results are notated as, e.g., PiMM, where Pi stands for protease inhibitor and "MM" is the banding pattern of that person.

Other detection methods include use of enzyme-linked-immuno-sorbent-assays in vitro and radial immunodiffusion.

Alpha 1-antitrypsin levels in the blood depend on the genotype. Some mutant forms fail to fold properly and are, thus, targeted for destruction in the proteasome, whereas others have a tendency to polymerize, thereafter being retained in the endoplasmic reticulum. The serum levels of some of the common genotypes are:

- PiMM: 100% (normal)

- PiMS: 80% of normal serum level of A1AT

- PiSS: 60% of normal serum level of A1AT

- PiMZ: 60% of normal serum level of A1AT

- PiSZ: 40% of normal serum level of A1AT

- PiZZ: 10-15% (severe alpha-1 antitrypsin deficiency)

The diagnosis is made in a patient with history of significant alcohol intake who develops worsening liver function tests, including elevated bilirubin and aminotransferases. The ratio of aspartate aminotransferase to alanine aminotransferase is usually 2 or more. In most cases, the liver enzymes do not exceed 500. The changes on liver biopsy are important in confirming a clinical diagnosis.

Ultrasound is routinely used in the evaluation of cirrhosis. It may show a small and nodular liver in advanced cirrhosis along with increased echogenicity with irregular appearing areas. Other liver findings suggestive of cirrhosis in imaging are an enlarged caudate lobe, widening of the fissures and enlargement of the spleen. An enlarged spleen (splenomegaly), which normally measures less than 11–12 cm in adults, is suggestive of cirrhosis with portal hypertension, in the right clinical context. Ultrasound may also screen for hepatocellular carcinoma, portal hypertension, and Budd-Chiari syndrome (by assessing flow in the hepatic vein).

Cirrhosis is diagnosed with a variety of elastography techniques. Because a cirrhotic liver is generally stiffer than a healthy one, imaging the liver's stiffness can give diagnostic information about the location and severity of cirrhosis. Techniques used include transient elastography, acoustic radiation force impulse imaging, supersonic shear imaging and magnetic resonance elastography. Compared to a biopsy, elastography can sample a much larger area and is painless. It shows a reasonable correlation with the severity of cirrhosis.

Other tests performed in particular circumstances include abdominal CT and liver/bile duct MRI (MRCP).

There are a number of diagnostic tests for , including HCV antibody enzyme immunoassay or ELISA, recombinant immunoblot assay, and quantitative HCV RNA polymerase chain reaction (PCR). HCV RNA can be detected by PCR typically one to two weeks after infection, while antibodies can take substantially longer to form and thus be detected.

Chronic is defined as infection with the virus persisting for more than six months based on the presence of its RNA. Chronic infections are typically asymptomatic during the first few decades, and thus are most commonly discovered following the investigation of elevated liver enzyme levels or during a routine screening of high-risk individuals. Testing is not able to distinguish between acute and chronic infections. Diagnosis in the infant is difficult as maternal antibodies may persist for up to 18 months.

While Gilbert's syndrome is considered harmless, it is clinically important because it may give rise to a concern about a blood or liver condition, which could be more dangerous. However, these conditions have additional indicators:

- Hemolysis can be excluded by a full blood count, haptoglobin, lactate dehydrogenase levels, and the absence of reticulocytosis (elevated reticulocytes in the blood would usually be observed in haemolytic anaemia).

- Viral hepatitis can be excluded by negative blood samples for antigens specific to the different hepatitis viruses.

- Cholestasis can be excluded by normal levels of bile acids in plasma, the absence of lactate dehydrogenase, low levels of conjugated bilirubin, and ultrasound scan of the bile ducts.

- More severe types of glucuronyl transferase disorders such as Crigler–Najjar syndrome (types I and II) are much more severe, with 0–10% UGT1A1 activity, with sufferers at risk of brain damage in infancy (type I) and teenage years (type II).

- Dubin–Johnson syndrome and Rotor syndrome are rarer autosomal recessive disorders characterized by an increase of conjugated bilirubin.

- In GS, unless another disease of the liver is also present, the liver enzymes ALT/SGPT and AST/SGOT, as well as albumin, are within normal ranges.

Effective treatment of the disease has been confined to liver transplants. Success has also been reported with an antioxidant chelation cocktail, though its effectiveness cannot be confirmed. Based on the alloimmune cause hypothesis, a new treatment involving high-dose immunoglobulin to pregnant mothers who have had a previous pregnancy with a confirmed neonatal hemochromatosis outcome, has provided very encouraging results.

In the early stages, patients with ALD exhibits subtle and often no abnormal physical findings. It is usually not until development of advanced liver disease that stigmata of chronic liver disease become apparent. Early ALD is usually discovered during routine health examinations when liver enzyme levels are found to be elevated. These usually reflect alcoholic hepatic steatosis. Microvesicular and macrovesicular steatosis with inflammation are seen in liver biopsy specimens. These histologic features of ALD are indistinguishable from those of nonalcoholic fatty liver disease. Steatosis usually resolves after discontinuation of alcohol use. Continuation of alcohol use will result in a higher risk of progression of liver disease and cirrhosis. In patients with acute alcoholic hepatitis, clinical manifestations include fever, jaundice, hepatomegaly, and possible hepatic decompensation with hepatic encephalopathy, variceal bleeding, and ascites accumulation.Tender hepatomegaly may be present, but abdominal pain is unusual. Occasionally, the patient may be asymptomatic.

In people with alcoholic hepatitis, the serum aspartate aminotransferase (AST) to alanine aminotransferase (ALT) ratio is greater than 2:1.AST and ALT levels are almost always less than 500. The elevated AST to ALT ratio is due to deficiency of pyridoxal-6-phosphate, which is required in the ALT enzyme synthetic pathway. Furthermore, alcohol metabolite–induced injury of hepatic mitochondria results in AST isoenzyme release. Other laboratory findings include red blood cell macrocytosis (mean corpuscular volume > 100) and elevations of serum γ-glutamyl transferase, alkaline phosphatase, and bilirubin levels. Folate level is reduced in alcoholic patients due to decreased intestinal absorption, increased bone marrow requirement for folate in the presence of alcohol, and increased urinary loss.The magnitude of leukocytosis reflects severity of liver injury. Histologic features include Mallory bodies, giant mitochondria, hepatocyte necrosis, and neutrophil infiltration at the perivenular area. Mallory bodies, which are also present in other liver diseases, are condensations of cytokeratin components in the hepatocyte cytoplasm and do not contribute to liver injury.Up to 70% of patients with moderate to severe alcoholic hepatitis already have cirrhosis identifiable on biopsy examination at the time of diagnosis.

The gold standard for diagnosis of cirrhosis is a liver biopsy, through a percutaneous, transjugular, laparoscopic, or fine-needle approach. A biopsy is not necessary if the clinical, laboratory, and radiologic data suggests cirrhosis. Furthermore, there is a small but significant risk of complications from liver biopsy, and cirrhosis itself predisposes for complications caused by liver biopsy. The best predictors of cirrhosis are ascites, platelet count <160,000/mm3, spider angiomata, and a Bonacini cirrhosis discriminant score greater than 7.

Four subtypes are recognised, but the clinical utility of distinguishing subtypes is limited.

1. positive ANA and SMA, elevated immunoglobulin G (classic form, responds well to low dose steroids);

2. positive LKM-1 (typically female children and teenagers; disease can be severe), LKM-2 or LKM-3;

3. positive antibodies against soluble liver antigen (this group behaves like group 1) (anti-SLA, anti-LP)

4. no autoantibodies detected (~20%) (of debatable validity/importance)

Most patients presenting with jaundice will have various predictable patterns of liver panel abnormalities, though significant variation does exist. The typical liver panel will include blood levels of enzymes found primarily from the liver, such as the aminotransferases (ALT, AST), and alkaline phosphatase (ALP); bilirubin (which causes the jaundice); and protein levels, specifically, total protein and albumin. Other primary lab tests for liver function include gamma glutamyl transpeptidase (GGT) and prothrombin time (PT).

Some bone and heart disorders can lead to an increase in ALP and the aminotransferases, so the first step in differentiating these from liver problems is to compare the levels of GGT, which will only be elevated in liver-specific conditions. The second step is distinguishing from biliary (cholestatic) or liver (hepatic) causes of jaundice and altered laboratory results. The former typically indicates a surgical response, while the latter typically leans toward a medical response. ALP and GGT levels will typically rise with one pattern while aspartate aminotransferase (AST) and alanine aminotransferase (ALT) rise in a separate pattern. If the ALP (10–45 IU/L) and GGT (18–85) levels rise proportionately about as high as the AST (12–38 IU/L) and ALT (10–45 IU/L) levels, this indicates a cholestatic problem. On the other hand, if the AST and ALT rise is significantly higher than the ALP and GGT rise, this indicates an hepatic problem. Finally, distinguishing between hepatic causes of jaundice, comparing levels of AST and ALT can prove useful. AST levels will typically be higher than ALT. This remains the case in most hepatic disorders except for hepatitis (viral or hepatotoxic). Alcoholic liver damage may see fairly normal ALT levels, with AST 10x higher than ALT. On the other hand, if ALT is higher than AST, this is indicative of hepatitis. Levels of ALT and AST are not well correlated to the extent of liver damage, although rapid drops in these levels from very high levels can indicate severe necrosis. Low levels of albumin tend to indicate a chronic condition, while it is normal in hepatitis and cholestasis.

Lab results for liver panels are frequently compared by the magnitude of their differences, not the pure number, as well as by their ratios. The AST:ALT ratio can be a good indicator of whether the disorder is alcoholic liver damage (above 10), some other form of liver damage (above 1), or hepatitis (less than 1). Bilirubin levels greater than 10x normal could indicate neoplastic or intrahepatic cholestasis. Levels lower than this tend to indicate hepatocellular causes. AST levels greater than 15x tends to indicate acute hepatocellular damage. Less than this tend to indicate obstructive causes. ALP levels greater than 5x normal tend to indicate obstruction, while levels greater than 10x normal can indicate drug (toxic) induced cholestatic hepatitis or Cytomegalovirus. Both of these conditions can also have ALT and AST greater than 20× normal. GGT levels greater than 10x normal typically indicate cholestasis. Levels 5–10× tend to indicate viral hepatitis. Levels less than 5× normal tend to indicate drug toxicity. Acute hepatitis will typically have ALT and AST levels rising 20–30× normal (above 1000), and may remain significantly elevated for several weeks. Acetaminophen toxicity can result in ALT and AST levels greater than 50x normal.

Many herbal and antioxidant remedies have been advocated for chronic liver disease but the evidence is not conclusive. Some support may be found in the orthodox medical use of two of these: N-acetyl cysteine (NAC), is the treatment of choice for acetaminophen overdose; both NAC and milk-thistle (Silybum marianum) or its derivative silibinin are used in liver poisoning from certain mushrooms, notably amanita phalloides, although the use of milk-thistle is controversial. Some common herbs are known or suspected to be harmful to the liver, including black cohosh, ma huang, chaparral, comfrey, germander, greater celandine, kava, mistletoe, pennyroyal, skull cap and valerian.

The diagnosis of autoimmune hepatitis is best achieved with a combination of clinical, laboratory, and histological findings after excluding other etiological factors (e.g. viral, hereditary, metabolic, cholestatic, and drug-induced diseases).

A number of specific antibodies found in the blood (antinuclear antibody (ANA), anti-smooth muscle antibody (SMA), anti-liver kidney microsomal antibodies (LKM-1, LKM-2, LKM-3), anti soluble liver antigen (SLA), liver–pancreas antigen (LP), and anti-mitochondrial antibody (AMA)) are of use, as is finding an increased Immunoglobulin G level. However, the diagnosis of autoimmune hepatitis always requires a liver biopsy.

Expert opinion has been summarized by the International Autoimmune Hepatitis Group, which has published criteria which utilize clinical and laboratory data that can be used to help determine if a patient has autoimmune hepatitis.

A calculator based on those criteria is available online.

Overlapping presentation with primary biliary cirrhosis and primary sclerosing cholangitis has been observed.

The condition is sometimes confused with juvenile hemochromatosis, which is a hereditary hemochromatosis caused by mutations of a gene called hemojuvelin. While the symptoms and outcomes for these two diseases are similar, the causes appear to be different.

A number of different tests are available to determine the degree of cirrhosis present. Transient elastography (FibroScan) is the test of choice, but it is expensive. Aspartate aminotransferase to platelet ratio index may be used when cost is an issue.

At present this can only be made definitively by liver biopsy or post mortem examination. Given the isolation of a causative virus it should soon be possible to diagnose this by serology, polymerase chain reaction or viral culture. On necropsy, the liver will be small, flaccid, and "dish-rag" in appearance. It has a mottled and bile stained surface. On microscopy there is marked centrilobular to midzonal hepatocellular necrosis and a mild to moderate mononuclear infiltrate. Mild to moderate bile duct proliferation may also be present. On radiology, the liver may be shrunken and difficult to visualize on ultrasound. Ascites may be present.

The tests, called assays, for detection of virus infection involve serum or blood tests that detect either viral antigens (proteins produced by the virus) or antibodies produced by the host. Interpretation of these assays is complex.

The surface antigen (HBsAg) is most frequently used to screen for the presence of this infection. It is the first detectable viral antigen to appear during infection. However, early in an infection, this antigen may not be present and it may be undetectable later in the infection as it is being cleared by the host. The infectious virion contains an inner "core particle" enclosing viral genome. The icosahedral core particle is made of 180 or 240 copies of the core protein, alternatively known as core antigen, or HBcAg. During this 'window' in which the host remains infected but is successfully clearing the virus, IgM antibodies specific to the core antigen ("anti-HBc IgM") may be the only serological evidence of disease. Therefore, most diagnostic panels contain HBsAg and total anti-HBc (both IgM and IgG).

Shortly after the appearance of the HBsAg, another antigen called e antigen (HBeAg) will appear. Traditionally, the presence of HBeAg in a host's serum is associated with much higher rates of viral replication and enhanced infectivity; however, variants of the virus do not produce the 'e' antigen, so this rule does not always hold true. During the natural course of an infection, the HBeAg may be cleared, and antibodies to the 'e' antigen ("anti-HBe") will arise immediately afterwards. This conversion is usually associated with a dramatic decline in viral replication.

If the host is able to clear the infection, eventually the HBsAg will become undetectable and will be followed by IgG antibodies to the surface antigen and core antigen ("anti-HBs" and "anti HBc IgG"). The time between the removal of the HBsAg and the appearance of anti-HBs is called the window period. A person negative for HBsAg but positive for anti-HBs either has cleared an infection or has been vaccinated previously.

Individuals who remain HBsAg positive for at least six months are considered to be carriers. Carriers of the virus may have chronic hepatitis B, which would be reflected by elevated serum alanine aminotransferase (ALT) levels and inflammation of the liver, if they are in the immune clearance phase of chronic infection. Carriers who have seroconverted to HBeAg negative status, in particular those who acquired the infection as adults, have very little viral multiplication and hence may be at little risk of long-term complications or of transmitting infection to others.

PCR tests have been developed to detect and measure the amount of HBV DNA, called the viral load, in clinical specimens. These tests are used to assess a person's infection status and to monitor treatment. Individuals with high viral loads, characteristically have ground glass hepatocytes on biopsy.