Blood is drawn from a vein on the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic, and an elastic band is placed around the upper arm to apply pressure and restrict blood flow through the vein. This causes veins below the band to fill with blood.

A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

For an infant or young child, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. Cotton or a bandage may be applied to the puncture site if there is any continued bleeding.

These tests are performed to detect infection by hepatitis-causing viruses. Hepatitis is an inflammation of the liver. Three common viruses can cause hepatitis -- the viruses are called Hepatitis A, Hepatitis B, and Hepatitis C.

Hepatitis A virus (HAV) is usually spread when something contaminated with infected stool is placed in the mouth. It has an incubation period of 2 to 6 weeks.

Hepatitis B virus (HBV) is most frequently transmitted by blood contact, but can also be transmitted through other body fluids. HBV can cause a severe and unrelenting form of hepatitis ending in liver failure and death. The incidence of HBV is higher among blood transfusion recipients, male homosexuals, dialysis patients, organ transplant patients, and IV drug users. It has a long incubation period (5 weeks to 6 months).

The Hepatitis B virus is made up of an inner core surrounded by an outer capsule. The outer capsule contains a protein called HBsAg (Hep B surface antigen). The inner core contains HBcAg (Hep B core antigen). A third protein called HBeAg is also found within the core. In addition to detecting Hepatitis B virus itself, tests can detect antibodies a patient has made to these antigens. The antibodies are called HBsAb, HBcAb, and HBeAb.

Hepatitis C virus (HCV) is transmitted in a manner similar to Hepatitis B. The incubation period is 2 to 12 weeks after exposure. The symptoms and course of the illness are similar to HBV.

Hepatitis D only causes disease when Hepatitis B is also present. It is not routinely checked on a hepatitis antibody panel.

Serology tests have been developed to detect the presence of antibodies to each of the hepatitis viruses in serum. IgM antibodies appear 3 to 4 weeks after exposure and usually return to normal in about 8 weeks. IgG antibodies appear about 2 weeks after the IgM antibodies start to increase; such antibodies may persist forever.

If the IgM antibody is elevated in the absence of IgG antibody, acute hepatitis is suspected. If IgG antibody is increased, but not IgM antibody, a convalescent or chronic state is likely.

Positive tests may indicate:

• Hepatitis A
• Hepatitis B
• Hepatitis C
• chronic Hepatitis B or Hepatitis B carrier state
• Hepatitis D, when found in conjunction with Hepatitis B

• chronic persistent hepatitis
• delta agent (Hepatitis D)
• nephrotic syndrome

The risks associated with having blood drawn are:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)
• Multiple punctures to locate veins