April 2005
Feature Story
CAP TODAY published an article in November 2000 about Nancy Cornish,
MD, Director of Microbiology, Methodist Hospital and Children’s Hospital,
Omaha, who is working to improve physician test-ordering. She teaches
Methodist’s physicians about lab tests through periodic clinical briefs,
which she writes and distributes. The response of CAP TODAY readers
to Dr. Cornish’s work was so enthusiastic and the requests for copies
of her briefs so numerous that we asked her to share the clinical briefs
she writes as they become available. Here, this month, is her word on
hepatitis C virus infection.
Chronic hepatitis C virus infection is now a disease that can be treated.
The introduction of pegylated interferons in combination with ribavirin
cures HCV infection in over 50 percent of adults. Chronic infection is
defined as the presence of HCV RNA in the blood for more than six months.
Facts about HCV infection include the following:
- Most common chronic bloodborne infection in the U.S.
- Leading cause of cirrhosis in the U.S.
- 10,000 to 20,000 deaths per year, and this number is expected to triple
in the next 10 to 20 years. Compares to colon cancer at 30,000 deaths
per year.
- Associated with an increased risk of liver cancer.
- Most common reason for liver transplant in the U.S.
Health care professionals in primary care, specialty, and public health
settings should routinely question patients about risk factors for HCV
infection. Routine HCV testing is recommended for the following groups:
- Persons who ever injected illegal drugs, including those who injected
once or a few times many years ago.
- Persons who received a blood transfusion or organ transplant before
July 1992.
- Persons who received clotting factor concentrates before 1987.
- Persons who were ever on long-term dialysis.
- Children (after 18 months of age) born to HCV-positive women.
- Health care, emergency medical, and public safety workers after needlesticks,
sharps, or mucosal exposures to HCV-positive blood.
- Persons with evidence of chronic liver disease.
- HIV-positive patients.
It is estimated that the virus can remain viable on unclean surfaces
for up to four days and perhaps longer. Therefore, sharing household items
such as nail clippers, toothbrushes, or razors should be discouraged in
family members or others who share a house with somebody with documented
hepatitis C infection. Because the risk of infection is low, routine testing
for hepatitis is not recommended for individuals living with an infected
person or having sex with an infected steady partner. However, these individuals
should be tested if they request it. Other risk factors that may lead
to blood exposure and to consider when talking to patients are sex with
multiple partners or prostitutes, sexual practices that lead to traumas,
intranasal cocaine use, tattoos, body piercing, and manicures. However,
in many patients infected with hepatitis C, the source of the infection
may never be identified.
Hepatitis C virus is an RNA virus transmitted via blood. It has six major
genotypes and 50 subtypes. Genotype 1 causes 70 percent to 75 percent
of infections in the U.S. and is characterized by a lower rate of response
to treatment (50 percent cure rate). Genotypes 2 and 3 have a much better
response to treatment (80 percent cure rate). It is estimated that 85
percent of adults who are infected with hepatitis C go on to have chronic
infection. Chronic infection is promoted by a high rate of viral mutation,
lack of a vigorous host T-cell response, and replication in hepatocytes
without cytotoxicity.
Approximately 1.8 percent of the U.S. population is infected (approximately
four million people). The highest prevalence is in the 40-year to 60-year
age range. Infection is usually asymptomatic; thus most people are unaware
of their disease. Acute infection, though rarely recognized, has an incubation
period of two to 26 weeks. Viral RNA is detected first, and shortly thereafter
antibodies develop. Only 15 percent of those infected go on to spontaneously
cure their disease. In practice, most people are diagnosed when routine
blood tests reveal abnormal liver chemistries, they donate blood, or a
physician notes risk factors and screens for the disease. Many people
present for the first time with end-stage liver disease. Patients may
present with extra-hepatic manifestations of chronic disease, which include
rheumatoid symptoms, keratoconjunctivitis sicca, lichen planus, glom er
ulo ne phri tis, lymphoma, essential mixed cryoglobulinemia, porphyria
cutanea tarda, and depression.
Because testing for the presence of hepatitis C is complicated and false-positive
and false-negative results occur, an algorithm for the use of laboratory
tests to diagnose patients with hepatitis C has been developed by the
Centers for Disease Control and Prevention. This algorithm (Related article:
Reflex hepatitis C testing protocol)
is designed to be cost-effective and produce accurate results. The tests
available for diagnosis of hepatitis C are as follows:
HCV antibody screening test (EIA)
Advantages of this test:
- Reproducible, inexpensive, FDA-approved for use.
- Suitable for screening at-risk populations and those with clinical
liver disease.
- Negative results are sufficient to exclude diagnosis of chronic HCV
infection in immunocompetent patients.
Disadvantages of this test:
- Positive results of screening tests must be confirmed by more specific
tests.
- False-negatives may occur in hemodialysis and immunodeficient patients.
- Negative results may occur in acute infections as antibodies may take
up to six weeks to develop after onset of symptoms of acute hepatitis.
HCV antibody confirmation Recombinant Immuno Blot Assay, or RIBA
Advantages of this test:
- FDA-approved for confirmatory testing of positive antibody screening
test.
- High specificity in detection of antibodies.
- Can be performed on same serum submitted for initial antibody screening
test.
Disadvantages of this test:
- Positive result does not distinguish between past infection or chronic
disease.
- Extra test which may not be needed in patient with high likelihood
of having disease.
- Needed to confirm positive results in infected persons who have spontaneous
cure of disease and those with probable false-positive results in the
antibody screening assay.
HCV RNA quantitative PCR (viral load)
This test detects viral RNA. The lower limit of detection is 200 IU/mL
(500 RNAcopies per mL). Results are reported as IU/mL.
Advantages of this test:
- Can be used as supplemental test in patient suspected of having chronic
disease with a positive antibody screening test.
- Can be used for diagnosis of acute infection and in immunodeficient
patients suspected of having disease with a negative antibody screen
test.
- Used to monitor therapy in patients with chronic disease.
Disadvantages of this test:
- HCV RNA can be transiently negative in persons with acute infection
but they can still go on to develop chronic infection.
- HCV RNA can be intermittently positive in patients with chronic infection.
- Use as supplemental test is valid only when the test is positive,
that is, patient has detectable viral load.
- Special handling of serum sample collected for testing is
necessary for accurate results; if specimen is not collected or transported
properly, false-negative results may be reported.
- False-positive results can occur through contamination.
HCV genotype
This test categorizes type of viral RNA present (performed via PCR and
subsequent nucleic acid sequencing).
Advantages of this test:
- Essential test to perform once to evaluate patient before
start of therapy.
- Results determine what dose and type of medication and length of treatment
will be used.
- May help identify source of infection.
- Assess likelihood of response to therapy.
Disadvantages of this test:
- Results may not be obtainable in patients with low viral loads (less
than 1,000 RNA copies per mL) or in cases where there are mixed genotypes
causing infection.
- Special handling of serum sample collected is necessary for
accurate results; if specimen is not collected or transported properly,
false-negative results may be reported.
HCV RNA qualitative PCR
This test detects viral RNA. It has a lower limit of detection of 50
IU/mL (100 RNA copies per mL). Results are reported as negative or positive
for HCV RNA.
Advantages of this test:
- Most sensitive PCR test available.
- Used clinically at end of treatment and at end of followup, to assess
treatment response.
- Used as confirmation of initial negative quantitative PCR test.
Disadvantages of this test:
- Special handling of serum sample collected is necessary for
accurate results; if specimen is not collected or transported properly,
may have false-negative results.
Other tests
Liver function tests and liver biopsies are not sensitive or specific
enough to be used for screening. They may be the initial test that triggers
testing for hepatitis C, and they are used as adjunct tests by specialists
in treatment of hepatitis C who are caring for patients with the disease.
Flow chart
The HCV antibody screen that we offer gives us the ability to separate
probable false-positive reactions from true-positive reactions by means
of a signal-to-cutoff ratio.
- Positive screens that have a low signal-to-cutoff ratio (<3.8) will
be automatically reflexed to a RIBA confirmatory test before reporting
the antibody screen. If the RIBA is negative, the screen will be reported,
the patient will be considered not infected with hepatitis C, and the
screen will be considered to be a false-positive.
- If the RIBA is positive, which should happen rarely with a low signal-to-cutoff
ratio, the physician will be called and blood obtained for a hepatitis
C virus quantitative PCR and, if positive, reflex to genotype if possible
and clinically appropriate.
- If the PCR quantitative test is positive, the genotype will be done
and the patient considered to have active infection with hepatitis
C and recommended for evaluation by a specialist in hepatitis C disease.
- If the PCR is negative, then the patient may be one of the 15 percent
who has spontaneous cure of the disease, in which case he or she will
be positive for hepatitis C antibodies but negative for active disease
by the PCR results (no viral RNA detected). A comment will be in the
report that a single negative PCR result does not rule out active infection,
and a second PCR (qualitative test) is recommended within a month.
- However, if the HCV antibody screen has a high signal-to-cutoff ratio
(> to 3.8), this indicates the patient has a greater than
95 percent chance of truly being infected. The physician will be called
and blood obtained for the supplemental tests. The supplemental test
to confirm the antibody screen in this case will be a hepatitis C virus
quantitative PCR.
- If this is positive, the specimen will automatically have a genotype
done and the patient will be considered to have active infection with
hepatitis C and recommended for evaluation by a specialist in hepatitis
C disease.
- If the PCR quantitative is negative, the specimen will automatically
be reflexed to a RIBA confirmatory test. If negative, the screen result
would be reported and the patient considered not infected with hepatitis
C (false-positive antibody screen). If the RIBA is positive, then the
patient is positive for hepatitis C antibodies and a single negative
PCR result does not rule out active infection. The recommendation is
a second PCR (qualitative) in a month to confirm spontaneous cure.
Children
Infection in children is not as common as in adults, with a prevalence
of 0.2 percent in children under 12 years of age and 0.4 percent in children
12 to 19 years of age. Almost half of the children infected spontaneously
cure their disease. Of those chronically infected, less than 10 percent
go on to have chronic hepatitis and less than five percent progress to
cirrhosis.
Infants born to hepatitis C infected mothers have passively acquired
maternal antibody for up to 18 months after birth and, therefore, should
only be screened using an HCV antibody screening test after 18 months
of age. If earlier diagnosis is required, a qualitative PCR can be performed
at one to two months of age; however, a positive result doesn’t mean the
child will be chronically infected and false-positive results occur.
There are no FDA-licensed therapies for children younger than 18 years
of age. However, therapy may be indicated in select cases. Consultation
with a pediatric specialist with experience in treating HCV infections
in children is warranted.
Counseling of patients with HCV infection
All people with HCV infection should be considered infectious and informed
of the possibility of transmission to others, and they should refrain
from donating blood, organs, tissues, or semen. They should not share
toothbrushes, nail clippers, or razors. They should be counseled to avoid
hepatotoxic agents such as medications and alcohol. If they are susceptible,
they should be vaccinated against hepatitis A and B viruses.
References
- Guidelines for laboratory testing and result reporting of antibody
to hepatitis C virus. MMWR,
Feb. 7, 2003, vol. 52, no. RR-3. (Free CME credit at end of report.)
- National Institutes of Health, Consensus Statement of Management of
Hepatitis C: 2002, vol. 19, no. 3, June 10-12.
- American Academy of Pediatrics, Red Book, 26th ed., 2003.
Online references
- National Institutes of Health Web site;
www.health.nih.gov . Search under hepatitis C.
- CDC Web site; www.cdc.gov.
Search under hepatitis C. Online free CME credit can be obtained at
www2a.cdc.gov/ce/availableactivities.asp.
Toll-free number for additional clinical help is 1-888-4HEPCDC.
|
|
|
