What laboratory tests do I need to know about?
Separate laboratory tests can diagnose HBV infection and monitor people with chronic hepatitis B.
Hepatitis B is first diagnosed using a blood test that looks for certain antigens (fragments of HBV) and antibodies (produced by the immune system in response to HBV). Initial blood tests to diagnose HBV infection look for one antigen, HBsAg (the hepatitis B surface antigen), and two antibodies, anti-HBs (antibodies to the HBV surface antigen) and anti-HBc (antibodies to the HBV core antigen). Actually, two types of anti-HBc antibodies are produced: immunoglobulin M (IgM) antibodies and IgG antibodies. IgM antibodies are produced early in the course of infection. IgG antibodies are produced later in the course of infection and replace IgM antibodies.
The blood test used to check for HBV infection can be quite confusing, given that a number of different combinations of antigens and antibodies are possible and can mean different things. Here’s a look at the most important test results to know:
| Hepatitis B status | HBsAg | Anti-HBc (total) | Anti-HBc (IgM) | Anti-HBs |
| Never infected with the virus (consider getting the vaccine). | Negative | Negative | Negative | Negative |
| Infection likely took place over the last six months and is still active. | Positive | Positive | Positive | Negative |
| Infection likely took place over the past six months and is in the process of clearing. A false-positive is another possibly (HIV-positive people with this particular test result should have their HBV viral load checked). | Negative | Negative | Positive | Negative |
| Infection likely took place more than six months ago and has been successfully controlled by the immune system. | Negative | Positive | Negative | Positive |
| The vaccine was successfully given to prevent HBV infection. | Negative | Negative | Negative | Positive |
| Chronic HBV infection. | Positive | Positive | Negative | Negative |
Depending on these results, additional diagnostic tests may be necessary. Somebody who has never been infected with HBV or has been vaccinated against the virus does not require any additional testing. Someone who was recently infected with HBV and has acute hepatitis B may want to get another blood test after six months have passed to make sure that the necessary immune response has occurred. People with chronic HBV infection require additional testing to learn more about their hepatitis B.
If you have chronic hepatitis B, your health care provider will usually order additional tests to determine if the infection is active:
If you have chronic hepatitis B, your health care provider will usually order additional tests to determine if the infection is active:
| Additional Tests | |
 | HBeAg and anti-HBe: HBeAg is the hepatitis B envelope antigen, and anti-HBe are the antibodies produced against this antigen. If HBeAg is detectable in a blood sample, this means that the virus is still active in the liver (and can be transmitted to others). If HBeAg is negative and anti-HBe is positive, this generally means that the virus is inactive. However, this is not always the case. Some people with chronic hepatitis—especially those who have been infected with HBV for many years—may have what is known as a “precore” or “core variant” mutated form of HBV. This can cause HBeAg to be negative and anti-HBe to be positive, even though the virus is still active in the liver. |
| HBV viral load: This test measures the actual amount of HBV in a blood sample, which helps determine whether HBV is reproducing in the liver. In a person with detectable HBeAg, an HBV viral load greater than 20,000 international units per milliliter (IU/mL) of blood indicates that the virus is active and has the greatest potential to cause damage to the liver. Similarly, in a person with an HBeAg-negative chronic hepatitis B, an HBV viral load of greater than 2,000 IU/mL indicates that the virus is active and has the potential to cause damage to the liver. Generally speaking, if the HBV viral load is above these numbers, treatment is considered necessary. However, some experts believe that hepatitis B should be treated at any viral load, given that there is a risk of liver cancer developing even when the HBV viral load is low. |
| Liver Function Tests: One of the most important liver enzymes to look for is alanine aminotransferase (ALT), sometimes called SGPT on lab reports. An elevated ALT level indicates that the liver is not functioning properly and that there is a risk of permanent liver damage. During acute hepatitis B infection, ALT levels can be temporarily elevated, but this rarely leads to long-term liver problems. In chronic hepatitis B, ALT levels can be either periodically or consistently increased, indicating a higher risk of long-term liver damage. |
| HBV Genotype: There are actually eight different types, or “genotypes,” of HBV in the world. The differences between the eight genotypes are based on differences in HBV’s genetic structure. HBV genotypes B and C are common in Asia, whereas genotypes A and D occur frequently in Europe. Genotypes F and H are found in Central and South America. In the United States, we see genotypes A, B, C and D. There is still some debate regarding whether it is important to know a patient’s HBV genotype. However, studies have demonstrated that patients with HBV genotypes A or B are likely to have better responses to some treatments than patients with genotypes C or D. In turn, finding out the HBV genotype may have some value when choosing treatments for hepatitis B. |
| Imaging: Magnetic resonance imaging (MRI) and “triple-phase” computed tomography (CT or CAT) scans are becoming more common, less painful tests to look for changes in the liver, most notably liver cancer tumors. Some experts suggest that MRI and triple-phase CT scans are the best way to look for tumors in people who have cirrhosis of the liver. |
| Ultrasound: Like MRI and CT scans, ultrasound can be used to look for liver cancer tumors. Some experts suggest that ultrasound is an effective screening tool in people who do not have cirrhosis of the liver. |
| Alpha-fetoprotein (AFP): This test looks for high levels of AFP, a protein that is produced by cancerous liver cells. AFP is not a very sensitive test; ultrasound is generally preferred over AFP to look for liver cancer tumors. |
| Liver biopsy: Unfortunately, blood tests and imaging do not tell the whole story regarding the health of the liver. In turn, a liver biopsy may be needed to look for evidence of cirrhosis and liver cancer. A liver biopsy is usually performed on an outpatient basis in a hospital. Sometimes, a trained health care provider, such as a hepatologist or a gastroenterologist, can perform a liver biopsy in his or her office. An ultrasound sometimes helps identify the best location to make the biopsy. The patient lies on his or her back or slightly to the left side. The area of the skin where the biopsy will be done is carefully cleaned. Then, a local anesthetic agent is used to numb the skin and tissue below. A specially designed thin needle is inserted through the skin. At this point, the physician will instruct the patient to take a deep breath in and out, and to hold it for about five seconds. The needle is inserted into and out of the liver. This takes only one or two seconds. A slender piece of liver tissue is removed with the needle and is then processed in a laboratory. The entire procedure from start to finish lasts only 15 to 20 minutes. The patient then has to lie still for several hours to avoid the possibility of internal bleeding. There may be some discomfort in the chest or shoulder, but this is almost always temporary. There is still some debate regarding the value of liver biopsies. Some experts argue that they can be useful in figuring out how best to treat hepatitis B, whereas others argue that treatment decisions (including when to start and which medications to use) can usually be made using blood tests. |
Ref. http://www.hepmag.com/articles/2511_18747.shtml
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