Hepatitis Virus Tests
Hepatitis Virus Tests
Viral hepatitis is any type of liver inflammation caused by a viral infection. The three most common viruses now recognized to cause liver disease are hepatitis A (infectious hepatitis), hepatitis B (serum hepatitis), and hepatitis C (non-A, non-B hepatitis). Several other types of viral hepatitis have been recognized recently, including hepatitis D (delta hepatitis), hepatitis E (epidemic hepatitis), and hepatitis G. A seventh type called transfusion-transmitted virus (TTV), a single-stranded DNA virus, has been implicated in post transfusion hepatitis. Commercial tests are not yet available to screen for HGV, and TTV infections. All blood and blood products donated for transfusion in the United States are screened for hepatitis B and hepatitis C.
|Source: Pagana, K.D. and T.J. Pagana. Mosby's Diagnostic and Laboratory Test Reference. 3rd ed. St. Louis: Mosby, 1997.|
|HBsAg (hepatitis B surface antigen)||2-6 weeks/1-3 months||Indicates active infection.|
|If antigen level persists in blood, patient is considered a carrier.|
|HBsAb (hepatitis B surface antibody)||2-6 weeks/life||Patient is in convalescent stage. Antigen presence denotes immunity to HBV.|
|HBcAb (hepatitis B core antibody)||2 weeks/3-6 months||Indicates past infection.|
|Also present in patients with chronic hepatitis.|
|HBeAg (hepatitis B e-antigen)||3-5 days/2-4 weeks||Its presence correlates with early and active disease and high infectivity in acute HBV infection.|
|HBeAb (hepatitis B e-antibody)||1-4 weeks/4-6 years||Indicates convalescent stage and denotes decreased infectivity.|
The different types of viral hepatitis produce similar symptoms, but they differ in terms of transmission, clinical course, and prognosis. Common symptoms are jaundice, malaise, nausea, and anorexia. It is estimated that approximately 600,000 cases of viral hepatitis occur in the United States each year, about half being caused by hepatitis B virus (HBV). Viral hepatitis infection is diagnosed by identifying specific viral antigens and/or antibodies associated with each type of viral hepatitis. An antigen is a substance, usually a protein, that is foreign to the body. An antibody is a protein manufactured by lymphocytes, a type of white blood cell, to neutralize the antigen. Hepatitis testing is also used to monitor the course of viral hepatitis.
False negative and positive test results may occur in a small number of persons tested. Fibrin deposits, heterophile antibodies, sample carryover, and autoantibodies such as rheumatoid factor have been reported to cause false positive results for some hepatitis tests. Repeat testing of reactive samples eliminates most false positives. False negatives may be caused when antigen or antibody levels are too low to detect, as in the "window phase" of infection. This is defined as the period between initial infection and the appearance of IgG antibodies.
Hepatitis B vaccine is recommended for health care workers who may be exposed to blood or body fluids. Health care workers should be familiar with procedures for post-exposure prophylaxis. Standard (universal) precautions for prevention of exposure to bloodborne pathogens should be followed at all times. Health care staff working in hemodialysis and other high prevalence environments should request education regarding more strict precautions.
There are five major types of viral hepatitis. The diseases, along with the tests available to aid in diagnosis, are described below.
Hepatitis A infection, formerly called infectious hepatitis, is caused by the hepatitis A virus (HAV), a single-stranded RNA virus. It is usually a mild disease, most often spread by food and water contamination with fecal material containing the virus. HAV can also be spread by sexual contact. Virus can be detected in stool samples prior to symptoms and for approximately three months thereafter. However, the virus cannot be isolated from the blood. Two types of antibodies to HAV can be detected. IgM antibody (anti-HAV/IgM), appears approximately three to four weeks after exposure and returns to normal within three to six months. IgG (anti-HAV/IgG) appears approximately two weeks after the IgM begins to increase, remains positive for years, and can often be detected for life. A diagnosis of infection with hepatitis A virus is usually made when symptoms including jaundice occur along with elevated levels of transaminases and a positive test for either IgM or total anti-HVA. Transaminases are enzymes released into the plasma in large amounts in necrotic liver diseases. If anti-HAV/IgG is elevated without anti-HAV/IgM, a convalescent stage of HAV infection or prior infection is presumed. Enzyme immunoassay (EIA) and radioimmunoassay (RIA) are the methods used to measure anti-HAV. Molecular diagnostic assays for the detection of HAV in stools and tissues have been developed but are not available commercially.
Hepatitis B infections, formerly known as serum hepatitis, are caused by the hepatitis B virus (HBV), a double stranded DNA virus. The disease can be mild or severe, and it can be acute (of limited duration) or chronic (ongoing). It is usually spread by sexual contact with another infected person, or through contact with infected blood. It is also transmitted from mother to child at birth (vertical transmission).
The incubation period for HBV is longer than for HAV (six to 25 weeks versus two to six weeks). The disease ranges from mild (asymptomatic) to severe and lasts for one to six months. Mortality from HBV infection is 1-2%. Approximately 10% of adults and 25% of children with acute HBV infection will develop chronic disease. About 90% of infants who are infected at birth will develop chronic hepatitis or become carriers. Chronic hepatitis may last from 1-20 years and varies greatly in severity. It is usually followed by an asymptomatic phase which lasts for many years called the chronic carrier state. Chronic carriers are capable of transmitting the virus to others. Chronic HBV infection results in cirrhosis of the liver in about 2%, and hepatic carcinoma in about 40% of cases.
HBV, also called the Dane particle, is composed of an inner protein core surrounded by an outer protein capsule. The outer capsule contains the hepatitis B surface antigen (HBsAg), formerly called the Australia antigen, that is excreted by infected hepatocytes into the bloodstream. The inner core contains HBV core antigen (HBcAg), and HBV e-antigen (HBeAg). Antibodies to these antigens are called anti-HBs, anti-HBc, and anti-HBe. The diagnostic utility of tests for HBV infection is described below:
- Hepatitis B surface antigen (HBsAg). This is the first test for HBV to become abnormal. HBsAg is detected before the onset of clinical symptoms, peaks during the first week of symptoms, and usually disappears by the time the accompanying jaundice (yellowing of the skin and other tissues) begins to subside (three months). In a very small number of cases, HBsAg may disappear from the blood sooner, causing a negative test result before the presence of antibodies can be detected. HBsAg is commonly detected by a double antibody sandwich immunoassay. The presence of HBsAg indicates infection with HBV. The test will be positive in the acute, chronic, or carrier state. A positive test for both HBsAg and anti-HBs/IgM indicates an active HBV infection. A person is considered to be a chronic carrier if HBsAg persists in the blood for six or more months. Carriers test negative for anti-HBs, but test positive for total anti-HBc.
- Hepatitis B surface antibody (anti-HBs). This appears approximately one month after the disappearance of the HBsAg, signaling the end of the acute infection period. Anti-HBs is the antibody that demonstrates immunity after administration of the hepatitis B vaccine. Its presence also indicates immunity to subsequent infection. Failure to detect anti-HBs in a person who is positive for HBsAg signals the development of chronic hepatitis or a carrier state. Tests for anti-HBs use particles coated with HBsAg to bind antibodies in the plasma. The antibodies are detected using an enzyme labeled or radiolabeled anti-human immunoglobulin.
- Hepatitis B DNA (HBV DNA) can be measured in the serum of persons in both the acute and chronic phases. This is accomplished through sensitive DNA hybridization techniques. The viral DNA is amplified using the polymerase chain reaction (PCR), and the amplicon products are detected using an enzymeconjugated probe. This test measures the amount of virus in the blood and is used to monitor persons receiving antiviral therapy.
- Hepatitis B core antibody (anti-HBc). There are two tests, anti-HBc/IgM and total anti-HBc. The former detects only the IgM antibody to the core antigen and the latter detects both IgG and IgM antibodies to the core antigen. The IgM component is the first antibody produced in HBV infection. It appears just before acute hepatitis develops and remains elevated for six to 18 months. After this time the IgM anti-HBc will be undetectable. Anti-HBc (owing to the IgM component) will be the only hepatitis test that is positive during the "window phase" of infection. This is the period when HBsAg levels are too low to detect, and IgG antibodies have not yet developed. The IgG component appears shortly after the IgM. Although the level slowly declines, it remains detectable for years and often for life. Therefore, total anti-HBc is a marker that detects both current and prior infection. Total anti-HBc is positive in chronic HBV infection. Anti-HBc/IgM is typically negative in chronic infection. Testing for anti-HBc/IgM and total anti-HBc is similar to that for anti-HBs, except that the antigen used is HBc.
- Hepatitis B e-antigen (HBeAg). This test is used as an index of infection, rather than for diagnostic purposes. The presence of this antigen correlates with early and active disease, as well as with high infectivity in patients with acute HBV infection. When HBeAg levels persist in the blood, the development of chronic HBV infection is suspected. This test is also used to determine if antiviral therapy has been effective. Measurement of HBeAg is similar to HBsAg except that the antibody used is anti-HBe.
- Hepatitis B e-antibody (anti-HBe). This antibody rises after anti-HBc and correlates with the disappearance of HBeAg. Therefore, the presence of anti-HBe and disappearance of HBeAg signal recovery and indicate a reduced risk of infectivity in patients who have previously been HBeAg positive. Chronic hepatitis B and carriers can be positive for either HBeAg or anti-HBe, but are less infectious when anti-HBe is present. Anti-HBe can persist for years, but usually disappears earlier than anti-HBs or anti-HBc. Measurement is similar to anti-HBs except that HBeAg is used instead of HBsAg.
Hepatitis C, previously known as non-A, non-B hepatitis, is caused by the hepatitis C virus (HCV), a single-stranded RNA virus. Transmission is mainly via contact with blood through contaminated needles, tattoos, and other parenteral means. The incidence of HCV infection by sexual transmission or close contact is much less than for HBV. Vertical transmission occurs in about 5% of cases. The course of acute disease is variable but generally is mild and often asymptomatic. HCV is more likely than HBV to lead to chronic liver disease, possible liver failure, and the eventual need for a liver transplant. Chronic carrier states develop in more than 80% of patients, and chronic liver disease with cirrhosis develops in approximately 20%. Persons with HCV are also at risk for hepatic carcinoma.
Hepatitis C is detected by demonstrating the presence of anti-HCV in the blood (HCV serology). The test is a sandwich-type enzyme immunoassay and detects the IgG antibody to HCV. The addition of this test to those for HbsAg and anti-HBc has greatly reduced the incidence of post-transfusion hepatitis. Since false positive results do occur with this test, a positive finding is confirmed by a more specific test, the recombinant immunoblot assay (RIBA) which also measures anti-HCV. New tests are available to measure HCV RNA in the blood. These viral load tests make use of the reverse transcription-polymerase chain reaction (RT-PCR) and are helpful in measuring the effect of interferon and other antiviral treatments.
Hepatitis D, previously called delta hepatitis, is caused by the hepatitis D virus (HDV). This is a single stranded RNA virus that requires coinfection with HBV in order to enter the hepatocyte. The disease occurs only in those who have HBV surface antigen in the blood from a past or simultaneously occurring infection. Transmission is mainly through intravenous drug use via contaminated needles, and in persons who have received multiple transfusions, but experts believe that transmission may also occur through sexual contact. Infection usually causes severe (fulminant) hepatitis and has a mortality rate of approximately 30%. It is diagnosed by demonstrating IgG antibodies to HDV in plasma of persons with documented HBV infection. Although not available commercially, research methods for IgM anti-HDV and HDV RNA have been developed.
Hepatitis E, once called epidemic hepatitis, is caused by hepatitis E virus (HEV), a single stranded RNA virus. It is also called enteric non-A, non-B hepatitis. Infection with HBE is transmitted when water or food becomes contaminated with feces containing the virus. Although not frequent in the United States, epidemic outbreaks have occurred in many other countries worldwide. The incubation time and course of the disease is similar to hepatitis A. Hepatitis E is usually a self-limiting disease, and chronic infection is infrequent. However, it is associated with a high mortality rate (about 20%) when contracted during pregnancy. Infection with HEV is diagnosed by demonstrating antibodies to the virus in the plasma of an infected person.
Hepatitis virus tests require a blood sample. It is not necessary for the patient to withhold food or fluids before any of these tests, unless requested to do so by the physician. A nurse or phlebotomist usually collects the blood by venipuncture following standard precautions for prevention of exposure to bloodborne pathogens.
Pressure should be applied to the site of venipuncture.
Complications for these tests are minimal for the patient, but may include slight bleeding from the blood-drawing site, fainting or feeling lightheaded after venipuncture, or hematoma (blood accumulating under the puncture site).
Testing for hepatitis infection requires a panel of tests. A typical screening panel for acute hepatitis consists of tests for anti-HAV/IgM, HBsAg, and anti-HBc/IgM. A positive test for total antibodies to HAV or HBV may indicate current infection, prior infection, or vaccination for hepatitis B. Therefore, when positive, these tests are evaluated in conjunction with other tests, the patient's history, and clinical findings. Normal results are as follows:
- hepatitis A antibody (IgM or total): negative
- hepatitis B core antibody (IgM or total): negative
- hepatitis B e antibody: negative
- hepatitis B e-antigen: negative
- hepatitis B surface antigen: negative
- hepatitis C antibody: negative
- hepatitis D antibody: negative
- hepatitis E antibody: negative
A single positive total anti-HAV test may indicate hepatitis A infection or previous exposure to the virus because these antibodies persist so long in the bloodstream. A positive test for anti-HAV/IgM or evidence of a rising total anti-HAV titer confirms hepatitis A. A negative anti-HAV test rules out hepatitis A.
A positive test for HbsAg indicates acute or chronic hepatitis B infection or a carrier state. High levels of HBsAg that continue for three or more months after onset of acute infection suggest development of chronic hepatitis or carrier status. A positive test for total anti-HBc indicates current infection or previous exposure. A negative test for HbsAg and total anti-HBc rules out hepatitis. A positive test for anti-HBc/IgM indicates acute infection and may be the only HBV marker that is positive during the window phase of infection. Anti-HBc/IgM is not positive in the chronic phase of infection. Detection of anti-HBs signals late convalescence or recovery from infection. This antibody remains in the blood to provide immunity to reinfection. A positive test for HBeAg indicates acute infection and a high state of infectivity. Disappearance of HBeAg and appearance of anti-HBe indicates recovery from HBV infection.
Anti-HBc develops after exposure to hepatitis C.
Anti-HDV develops after exposure to hepatitis D.
Anti-HEV develops after exposure to hepatitis E.
Health care team roles
Hepatitis tests are ordered and interpreted by a physician. A phlebotomist, or sometimes a nurse, collects the blood, and a clinical laboratory scientist, CLS(NCA)/medical technologist, MT(ASCP) or clinical laboratory technician CLT(NCA)/medical laboratory technician MLT(ASCP) performs the testing.
Antibody— A protein manufactured by lymphocytes that binds to a specific antigen.
Antigen— A protein that is foreign to the body, not part of "self."
Lymphocyte— A type of white blood cell involved in the immune response.
Hepatitis A— Commonly called infectious hepatitis, caused by the hepatitis A virus (HAV). Most often spread by food and water contamination.
Hepatits B— Commonly known as serum hepatitis, it is caused by the hepatitis B virus (HBV). The disease can be mild or severe, and it can occur as an acute or chronic disease. Frequently spread by sexual contact with another infected person, contact with infected blood, intravenous drug use, or from mother to child at birth.
Hepatitis C— Hepatitis caused by the hepatitis C virus (HCV). Usually a milder form of the disease initially, but carries a greater chance to lead to chronic liver disease, possible liver failure, and the eventual need for transplant. Chronic carrier state is also a risk.
Ansari, M. Qasim. Immunologic Assessment of Infectious Diseases. In The Handbook of Clinical Pathology, 2nd ed. Chicago: American Society of Clinical Pathologists, 2000.
Chernecky, Cynthia, and Barbara Berger. Laboratory Tests and Diagnostic Procedures. Philadelphia: W. B. Saunders Company, 2001.
Henry, J.B., ed. Clinical Diagnosis and Management by Laboratory Methods, 20th ed. Philadelphia: W. B. Saunders Company, 2001.
Hodinka, Richard L. "Laboratory Diagnosis of Viral Hepatitis." In Viral Hepatitis: Diagnosis, Therapy, and Prevention. Totowa, NJ: Humana Press, 1999.
Pagana, Kathleen Deska. Mosby's Manual of Diagnostic and Laboratory Tests. St. Louis: Mosby, Inc., 1999.
Abbott Diagnostics, Div. Abbott Laboratories, North Chicago, IL 60064. 〈http://abbottdiagnostics.com/systems_tests/hepatitis/index.htm〉
Centers for Disease Control. "Hepatitis." April 22, 2001. Updated April 18, 2001. 〈http://www.cdc.gov/ncidod/diseases/hepatitis〉.
HealthWeb. April 22, 2001. Copyright 1995/2001. 〈http://www.healthweb.org〉.