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.

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.

The CDC recommends the routine vaccination of all children under the age of 19 with the hepatitis B vaccine. They also recommend it for those who desire it or are at high risk.

Routine vaccination for hepatitis B starts with the first dose administered as a shot into the muscle before the newborn is discharged from the hospital. An additional two doses should be administered before the child is 18 months.

For babies born to a mother with hepatitis B surface antigen positivity, the first dose is unique – in addition to the vaccine, the hepatitis immune globulin should also be administered, both within 12 hours of birth. These newborns should also be regularly tested for infection for at least the first year of life.

There is also a combination formulation that includes both hepatitis A and B vaccines.

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.

Hepatitis A can be prevented by vaccination, good hygiene, and sanitation.

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.

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.

Although HAV is excreted in the feces towards the end of the incubation period, specific diagnosis is made by the detection of HAV-specific IgM antibodies in the blood. IgM antibody is only present in the blood following an acute hepatitis A infection. It is detectable from 1-2 weeks after the initial infection and persists for up to 14 weeks. The presence of IgG antibodies in the blood means the acute stage of the illness has passed and the person is immune to further infection. IgG antibodies to HAV are also found in the blood following vaccination, and tests for immunity to the virus are based on the detection of this antibody.

During the acute stage of the infection, the liver enzyme alanine transferase (ALT) is present in the blood at levels much higher than is normal. The enzyme comes from the liver cells damaged by the virus.

Hepatovirus A is present in the blood (viremia) and feces of infected people up to 2 weeks before clinical illness develops.

A vaccine based on recombinant viral proteins was developed in the 1990s and tested in a high-risk population (in Nepal) in 2001. The vaccine appeared to be effective and safe, but development was stopped for lack of profitability, since hepatitis E is rare in developed countries. No hepatitis E vaccine is licensed for use in the United States.

Although other HEV vaccine trials have been successful, these vaccines have not yet been produced or made available to susceptible populations. The exception is China; after more than a year of scrutiny and inspection by China's State Food and Drug Administration (SFDA), a hepatitis E vaccine developed by Chinese scientists was available at the end of 2012. The vaccine—called HEV 239 by its developer Xiamen Innovax Biotech—was approved for prevention of hepatitis E in 2012 by the Chinese Ministry of Science and Technology, following a controlled trial on 100,000+ people from Jiangsu Province where none of those vaccinated became infected during a 12-month period, compared to 15 in the group given placebo. The first vaccine batches came out of Innovax' factory in late October 2012, to be sold to Chinese distributors.

Due to the lack of evidence, WHO did not make a recommendation regarding routine use of the HEV 239 vaccine. National authorities may however, decide to use the vaccine based on the local epidemiology.

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 vaccine for hepatitis B protects against hepatitis D virus because of the latter's dependence on the presence of hepatitis B virus for it to replicate.

Latest evidence suggests that Pegylated interferon alpha is effective in reducing the viral load and the effect of the disease during the time the drug is given, but the benefit generally stops if the drug is discontinued. The efficiency of the pegylated interferon treatment does not usually exceed ~20%.

The drug myrcludex B, which inhibits virus entry into hepatocytes, is in clinical trials .

In terms of treatment, ribavirin is not registered for hepatitis E treatment, though off-label experience for treating chronic hepatitis E with this compound exists. The use of low doses of ribavirin over a three-month period has been associated with viral clearance in about two-thirds of chronic cases. Other possible treatments include pegylated interferon or a combination of ribavirin and pegylated interferon. In general, chronic HEV infection is associated with immunosuppressive therapies, but remarkably little is known about how different immunosuppressants affect HEV infection. In individuals with solid-organ transplantation, viral clearance can be achieved by temporal reduction of the level of immunosuppression.

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 most characteristic feature are elevated levels of gamma glutamyl transferase (100–300 IU/L), aspartate transaminase (>1000 IU/L) and sorbitol dehydrogenase, with AST levels > 4000 IU/L indicating a poor prognosis. High levels of unconjugated and total bilirubin, and serum bile acids, can be seen. Moderate to severe acidosis, leukocytosis, polycythaemia, increased creatine kinase and hyperammonemia may be present, and hemolysis can occur at the end stage. The prothrombin time (PT) and partial thromboplastin time (PTT) is often prolonged. Subclinical horses may only show elevated liver enzymes without any other clinical signs. Horses are rarely hypoglycemic, but blood glucose monitoring is ideal to indicate which horses may be benefited by glucose treatment.

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)

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.

There is no specific treatment for neonatal hepatitis. Vitamin supplements are usually prescribed and many infants are given phenobarbital, a drug used to control seizures, but which also stimulates the liver to excrete additional bile. Formulas containing more easily digested fats are also given to the infant.

Neonatal hepatitis caused by the hepatitis A virus also usually resolves itself within six months, but cases that are the result of infection with the hepatitis B or hepatitis C viruses most likely will result in chronic liver disease. Infants who develop cirrhosis ultimately will need a liver transplant.

The most common cause of hepatitis is viral. Although they are classified under the disease hepatitis, these viruses are not all related.

"Hepatitis B" is caused by hepatitis B virus, a hepadnavirus that can cause both acute and chronic hepatitis. Chronic hepatitis develops in the 15% of adults who are unable to eliminate the virus after an initial infection. Identified methods of transmission include blood (blood transfusion, now rare), unsanitary tattoos, sexually (through sexual intercourse or through contact with blood or bodily fluids), or via mother to child by breast feeding (minimal evidence of transplacental crossing). However, in about half of cases the source of infection cannot be determined. Blood contact can occur by sharing syringes in intravenous drug use, shaving accessories such as razor blades, or touching wounds on infected persons. Needle-exchange programmes have been created in many countries as a form of prevention.

Patients with chronic hepatitis B have antibodies against hepatitis B, but these antibodies are not enough to clear the infection of the affected liver cells. The continued production of virus combined with antibodies is a likely cause of the immune complex disease seen in these patients. A vaccine is available that will prevent infection from hepatitis B for life. Hepatitis B infections result in 500,000 to 1,200,000 deaths per year worldwide due to the complications of chronic hepatitis, cirrhosis, and hepatocellular carcinoma. Hepatitis B is endemic in a number of (mainly South-East Asian) countries, making cirrhosis and hepatocellular carcinoma big killers. There are six treatment options approved by the U.S. Food and Drug Administration (FDA) available for persons with a chronic hepatitis B infection: alpha-interferon, pegylated interferon, adefovir, entecavir, telbivudine, and lamivudine. About 65% of persons on treatment achieve a sustained response.

The routes of transmission of hepatitis D are similar to those for hepatitis B. Infection is largely restricted to persons at high risk of hepatitis B infection, particularly injecting drug users and persons receiving clotting factor concentrates. Worldwide more than 15 million people are co-infected. HDV is rare in most developed countries, and is mostly associated with intravenous drug use. However, HDV is much more common in the immediate Mediterranean region, sub-Saharan Africa, the Middle East, and the northern part of South America. In all, about 20 million people may be infected with HDV.

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.

Blood for blood transfusion is screened for many bloodborne diseases. Additionally, a technique that uses a combination of riboflavin and UV light to inhibit the replication of these pathogens by altering their nucleic acids can be used to treat blood components prior to their transfusion, and can reduce the risk of disease transmission.

A technology using the synthetic psoralen, amotosalen HCl, and UVA light (320–400 nm) has been implemented in European blood centers for the treatment of platelet and plasma components to prevent transmission of bloodborne diseases caused by bacteria, viruses and protozoa.

There has been no specific drug therapy developed for hepatitis, with the exception of hepatitis C. Patients are advised to rest in the early stages of the illness, and to eat small, high-calorie, high-protein meals in order to battle anorexia. Larger meals are more easily tolerated in the morning, for patients often experience nausea later in the day. Although high-protein meals are recommended, protein intake should be reduced if signs of precoma — lethargy, confusion, and mental changes — develop.

In acute viral hepatitis, hospitalization is usually required only for patients with severe symptoms (severe nausea, vomiting, change in mental status, and PT greater than 3 seconds above normal) or complications. If the patient experiences continuous vomiting and is unable to maintain oral intake, parenteral nutrition may be required.

In order to relieve nausea and also prevent vomiting, antiemetics (diphenhydramine or prochlorperazine) may be given 30 minutes before meals. However, phenothiazines have a cholestatic effect and should be avoided. The resin cholestyramine may be given only for severe pruritus.

This remains a challenge in clinical practice due to a lack of reliable markers. Many other conditions lead to similar clinical as well as pathological pictures. To diagnose hepatotoxicity, a causal relationship between the use of the toxin or drug and subsequent liver damage has to be established, but might be difficult, especially when idiosyncratic reaction is suspected. Simultaneous use of multiple drugs may add to the complexity. As in acetaminophen toxicity, well established, dose-dependent, pharmacological hepatotoxicity is easier to spot. Several clinical scales such as CIOMS/RUCAM scale and Maria and Victorino criteria have been proposed to establish causal relationship between offending drug and liver damage. CIOMS/RUCAM scale involves a scoring system that categorizes the suspicion into "definite or highly probable" (score > 8), “probable” (score 6-8), “possible” (score 3-5), “unlikely” (score 1-2) and “excluded” (score ≤ 0). In clinical practice, physicians put more emphasis on the presence or absence of similarity between the biochemical profile of the patient and known biochemical profile of the suspected toxicity (e.g., cholestatic damage in amoxycillin-clauvonic acid ).

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.