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Back to Infections Lab Tests
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How is it used?
There are several tests used to detect the presence of hepatitis B
antibodies. Antibodies are produced by the body to offer protection
from antigens (foreign proteins).
The hepatitis B surface antibody (anti-HBs) is the most common test.
Its presence indicates previous exposure to HBV, but the virus is no
longer present and the person cannot pass on the virus to others. The
antibody also protects the body from future HBV infection. In addition
to exposure to HBV, the antibodies can also be acquired from
successful vaccination. This test is done following the completion of
vaccination against the disease or following an active infection.
Hepatitis B surface antigen (HBsAg) is a protein antigen produced by
HBV. This antigen is the earliest indicator of acute hepatitis B and
frequently identifies infected people before symptoms appear. In some
people (particularly those infected as children or those with a weak
immune system, such as those with AIDS), chronic infection with HBV
occurs.
Sometimes, HBV goes into “hiding” in the liver and other cells and
does not produce new viruses that can infect others, or produces them
in such low amounts that they cannot be found in the blood. People who
have this form are said to be carriers. In other cases, the body
continues to make viruses that can further infect the liver and can be
spread to other people. In both these cases, HBeAg will be positive.
The next test is helpful for distinguishing these two states.
Hepatitis B e-antigen (HBeAg) is a viral protein associated with HBV
infections. Unlike the surface antigen, the e-antigen is found in the
blood only when there are viruses also present. When the virus goes
into “hiding,” the e-antigen will no longer be present in the blood.
HBeAg is often used as a marker of ability to spread the virus to
other people (infectivity). Measurement of e-antigen may also be used
to monitor the effectiveness of HBV treatment; successful treatment
will usually eliminate HBeAg from the blood and lead to development of
antibodies against e-antigen (anti-HBe). There are some types
(strains) of HBV that do not make e-antigen; these are especially
common in the Middle East and Asia. In areas where these strains of
HBV are common, testing for HBeAg is not very useful.
Anti-hepatitis B core antigen (anti-HBc) is an antibody to the
hepatitis B core antigen. The core antigen is found on virus particles
but disappears early in the course of infection. This antibody is
produced during and after an acute HBV infection and is usually found
in chronic HBV carriers as well as those who have cleared the virus,
and usually persists for life.
HBV DNA is a more sensitive test than HBeAg for detecting viruses in
the blood stream. It is usually used in conjunction with – rather than
instead of – the regular serologic tests. It may be used to monitor
antiviral therapy in patients with chronic HBV infections.
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When is it ordered?
These tests are used to determine whether the vaccine has produced the
desired level of immunity as well as to diagnose and follow the course
of an infection.
In a patient with acute hepatitis, IgM anti-HBc and HBsAg are usually
ordered together to detect recent infection by HBV. In persons with
chronic hepatitis, or with elevated ALT or AST, HBsAg and anti-HBc are
usually done to see if the liver damage is due to HBV. If so, HBsAg
and HBeAg are usually measured on a regular basis (every 6 months to a
year), since in some people HBeAg (and, less commonly, HBsAg) will go
away on their own. In those who are being treated for chronic HBV,
HBeAg and HBV DNA can be used to determine whether the treatment is
successful. If a person is given the HBV vaccine, anti-HBs is used to
see if it successful; if levels of the antibody are over 10 IU/mL, the
person is probably protected for life from infection by HBV.
All donated blood is tested for the presence of the HBsAg before being
distributed.
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What does the test result mean?
Hepatitis B surface antibody (anti-HBs): a positive result indicates
immunity to hepatitis B from the vaccination or recovery from an
infection.
Hepatitis B surface antigen (HBsAg): A negative result indicates that
a person has recovered from acute hepatitis and has rid themselves of
the virus. A positive (or reactive) result indicates an active
infection but does not indicate whether the virus can be passed to
others.
Hepatitis B e-antigen (HBeAg): A positive (or reactive) result
indicates the presence of virus that can be passed to others. A
negative result usually means the virus cannot be spread to others,
except in parts of the world where infection with strains that cannot
make this protein are common.
Anti-hepatitis B core antigen (anti-HBc): If it is present with a
positive anti-HBs, it usually indicates recovery from an infection and
the person is not a carrier. In acute infection, the first type of
antibody to HBc to appear is an IgM antibody. Testing for this type of
antibody can prove whether a person has recently been infected by HBV
(where IgM anti-HBc would be positive) or for some time (where IgM
anti-HBc would be negative).
HBV DNA: A positive (or reactive) result indicates the presence of
virus that can be passed to others. A negative result usually means
the virus cannot be spread to others, especially if tests that can
pick up as few as 1,000 viruses (copies) in one mL of blood are used.
PLEASE NOTE: Numerically reported test results are interpreted
according to the test's reference range, which may vary by the
patient's age, sex, as well as the instrumentation or kit used to
perform the test. To learn more about reference ranges, please see the
article, Reference Ranges and What They Mean. To learn the reference
range for your test, consult your doctor or laboratorian.
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Is there anything else I should know?
While the tests described above are specific for HBV, other liver
function tests such as AST, ALT, and gamma-glutamyl transferase (GGT)
may be used to monitor the progress of the disease. In some cases, a
liver biopsy may be performed for confirmation.
Glucose, plasma, serum
Glucose levels in serum and plasma are used to diagnose and monitor
therapy in diabetes. Three main tests are used for the diagnosis of
diabetes according to the American Diabetic Association:
- Fasting plasma glucose
- Random plasma glucose test
- Two hours post-glucose load.
Methodology
Immunoassay, high performance liquid chromatography.
Reference levels
Fasting blood glucose
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Symptoms of diabetes plus a fasting
plasma glucose level of 126 mg/dL on two occasions after an 8 hour fast.
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If the measurement is between 110 and 126
this is impaired fasting glucose.
A glucose tolerance test should be performed.
It is reserved for patients without symptoms in which
fasting glucose test is nondiagnostic. It should be
done after an overnight fast. Results are valid only when the patient
is not under stress and physical activity is unrestricted and daily
carbohydrate intake is more than 150g/dL.
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Between 140 mg/dL to 200 mg/dL fasting glucose level denotes
impaired glucose tolerance. Whilst this condition is asymptomatic it carries
an increased risk of large vessel disease.
Random blood glucose
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A random plasma glucose of 200 mg /dL or
greater denotes diabetes.
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