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Today, we have M.D Tse-Ling Fong's comment on the issue about hepatitis disease, hope that a new light in your interest of the above.
Medical Author: Tse-Ling Fong, M.D.
Medical Editor: Leslie J. Schoenfield, M.D., Ph.D.
Dr. Fong is the Medical Director of the USC Liver Transplant Program and Associate Professor of Medicine at the USC Keck School of Medicine. He obtained his medical degree from the University of Southern California and completed his residency in Internal Medicine at Los Angeles County-USC Medical Center. He completed a Hepatology fellowship at the USC Liver Unit under the tutelage of Dr. Allan Redeker and Dr. Telfer Reynolds. He also completed a fellowship in Gastroenterology at Los Angeles County-USC Medical Center.
Dr Fong was a Clinical Associate with the Liver Diseases Section at the National Institutes of Health. He is board certified in Internal Medicine and the subspecialty of Gastroenterology. He was a full-time faculty at the USC Liver Unit at Rancho Los Amigos Medical Center and Assistant Professor of Medicine at USC School of Medicine from 1991-1996. He was Associate Director of Hepatology and Associate Medical Director of Liver Transplant at Cedars-Sinai Medical Center between 1996 and 2001.
Dr. Fong has over 40 peer-reviewed publications in the area of viral hepatitis, liver transplantation and other areas of liver diseases. He is a fellow of the American College of Physicians and members of the American Association for the Study of Liver Disease and Western Society for Clinical Investigation.
Here the summary of M.D Tse-Ling Fong's comment
01) What is the scope of the hepatitis C problem?
02) What is the nature (biology) of the hepatitis C virus (HCV)?
03) How does liver damage occur in hepatitis C infection?
04) What are the symptoms of hepatitis C infection?
05) What is the usual progression of chronic infection with hepatitis C virus?
06) Who is at high risk and should be tested for hepatitis C infection?
01) What is the scope of the hepatitis C problem?
The hepatitis C virus (HCV) is one of the most significant health problems affecting the liver. More than 4 million Americans (1.3% of the U.S. population) and 170 million individuals in the world (3% worldwide) are infected with hepatitis C virus. The prevalence (number of cases in a population at a specific time) of hepatitis C virus infections varies in different parts of the world. For example, the prevalence of hepatitis C virus in Scandinavia is less than 0.5% of the population, whereas the prevalence in Egypt is over 20%. In the U.S. and Western Europe, the complications of hepatitis C virus chronic hepatitis and cirrhosis are the most common reasons for liver transplantation.
One of the major problems with hepatitis C virus infections is that 85% of individuals initially infected with this virus will become chronically infected, usually for decades. The other 15% of hepatitis C virus infected individuals simply have an acute infection; that is, one that resolves spontaneously in a few weeks or months. The propensity of hepatitis C virus to cause chronic infection is explained by the extraordinary ability of this virus (in contrast to most other viruses, including hepatitis A) to avoid destruction by the body's immune defense system. (The immune system includes antibodies and specialized white blood cells, called lymphocytes).
Once established, chronic hepatitis C virus infection causes an inflammation of the liver called chronic hepatitis. This condition can progress to scarring of the liver, called fibrosis, or more advanced scarring, called cirrhosis. Some patients with cirrhosis will go on to develop liver failure or the complications of cirrhosis, including liver cancer.
In the U.S., the number of new cases of hepatitis C has declined over the last 10 years from a peak of some 200,000 annually to about 28,000 in 1999. This striking reduction is the result of a drop in the number of cases of acute hepatitis C among intravenous drug users. Perhaps this decrease among the drug users is due to changes in their practices brought on by their awareness of HIV infection. Furthermore, sensitive blood tests for the detection of hepatitis C virus became available to screen the blood supply and individuals at high risk for hepatitis C virus.
Indeed, with blood being routinely screened for hepatitis C virus, the risk of a single unit of blood transmitting hepatitis C today is less than 1 in 100,000. Still, because of the many individuals who became infected 10 to 20 years ago, the number of deaths (or the need for liver transplantation) due to the complications of chronic hepatitis C virus liver disease is expected to triple within the next decade or two. On the other hand, in recent years, our understanding of the hepatitis C virus and its management has increased substantially.
02) What is the nature (biology) of the hepatitis C virus (HCV)?
Hepatitis C virus is one of several viruses that can cause hepatitis, which is inflammation of the liver. It is unrelated to the other common hepatitis viruses (A, B, D, and E). Hepatitis C virus is a member of the Flaviviridae family of viruses. Other members of this family of viruses include those that cause yellow fever and dengue.
Viruses belonging to this family all have ribonucleic acid (RNA) as their genetic material. They are, therefore, referred to as RNA viruses. The RNA of hepatitis C virus is made up of almost 10,000 units called nucleotides that are organized to serve as the virus's genetic blue print for the manufacture of proteins. Thus, the virus contains structural proteins to build its structure, including its coat (envelope), and non-structural proteins (e.g., the enzyme polymerase) to carry out its functions. Understanding the nature (biology) of hepatitis C virus allows scientists to develop therapy that specifically targets the virus's structure or functions.
There are considerable differences in the genetic structure of hepatitis C virus. Accordingly, hepatitis C virus is categorized into six major genetic types (genotypes) and many more subtypes, based on the sequence (order) of nucleotides in the virus. Although the different genotypes are found throughout the world, there is a distinct distribution of genotypes in certain geographic regions. For instance, the most common genotype in the U.S. is genotype 1 (1a and 1b), which accounts for 80% of hepatitis C virus cases in the U.S.
The influence of genotype on the long-term prognosis of hepatitis C virus disease is still unclear. However, what is clear is that patients infected with genotypes 2 or 3 are much more likely to respond to interferon therapy. In contrast, patients infected with genotype 1 (particularly 1b) or genotype 4 do not respond very well to interferon therapy.
In addition, within a single host, there are minor genetic differences in the hepatitis C virus. These minor differences give rise to what are called quasispecies (quasi means resembling each other). Where do the quasispecies come from? Well, one of the non-structural hepatitis C virus proteins mentioned above is the enzyme polymerase. This enzyme is the machine that allows the virus to reproduce its genetic material (RNA) in order to multiply. Now, this RNA polymerase is very prone to making mistakes, resulting in changes (mutations) in the genetic material. The majority of these mutations result in a non-viable (not living) new quasispecies of hepatitis C virus, but sometimes the mutation results in viable quasispecies. With time, the accumulation of these viable mutations results in multiple quasispecies of the virus within the same host.
Why are there so many different varieties of hepatitis C virus anyway? Perhaps the different varieties confer an advantage to the survival of this virus over the years. For example, some of the new species may become more efficient in reproducing themselves (replication). By the same token, however, the genetic variability of hepatitis C virus has made the development of a protective vaccine against all of these genotypes and quasispecies a near impossible task with our present technology. Moreover, this variability probably also explains how this virus results in such a high rate of chronic infection. Thus, the genetic variability may enable the hepatitis C virus to avoid destruction by the host's cellular immune cells or antibodies, and so maintain (perpetuate) the chronic infection.
03) How does liver damage occur in hepatitis C infection?
The basis (mechanism) of liver damage in chronic hepatitis C virus infection is not very well understood. The virus itself probably does not cause liver cell damage directly. Indeed, the level of the virus in the blood does not correlate with the actual liver damage seen on the liver biopsy. Liver damage in chronic hepatitis C virus is probably caused by the interplay between the virus and the body's immune system, which includes cytotoxic (injurious to cells) lymphocytes and specific inflammatory messengers (cytokines).
How is hepatitis C virus spread and how can transmission be prevented?
Hepatitis C is spread (transmitted) most efficiently through the blood. Therefore, hepatitis C virus is transmitted by infected blood or blood products, transplantation of infected solid organs (e.g., liver, kidney, heart), and the sharing of contaminated needles among intravenous drug users. In retrospect, hepatitis C virus was the most common cause of hepatitis that resulted from blood transfusions in the 1980's. At that time, hepatitis C virus had not yet been identified and post-transfusion cases of hepatitis were called non-A non-B hepatitis.
In the early 1980's, the risk of contracting hepatitis C virus from a blood transfusion was as high as 15%. In the mid 1980's, when the practice of using commercial (paid) donors was stopped and blood was screened for the human immunodeficiency virus (HIV), the risk of post-transfusion hepatitis fell to about 5%. This risk was then cut in half when blood was screened with the substitute (surrogate) markers, elevated alanine aminotransferase (ALT, the liver enzyme), and hepatitis B core antibodies. Finally, the isolation of the hepatitis C virus and the development of a screening test for hepatitis C virus dramatically lowered the risk of acquiring hepatitis C virus infection through blood transfusions.
All blood donors are currently screened with the following panel; hepatitis C antibodies, hepatitis B surface antigen, hepatitis B core antibodies, elevated alanine aminotransferase, HIV antibodies, and syphilis. As a result, the risk of contracting hepatitis C virus from a single unit of blood is less than 1:100,000. This risk will be even lower one day when tests that measure minute quantities of hepatitis C viral nucleic acids are universally adopted for blood screening.
Today, hepatitis C virus is most commonly transmitted by intravenous drug abuse, which accounts for about 60% of new cases. Moreover, 50 to 60% of new intravenous drug users are infected within the first 6 months of use, and nearly 90% are infected by one year. Other types of illegal drug usage, such as snorting cocaine, have also been associated with an increased risk of acquiring an hepatitis C virus infection.
Hepatitis C virus can be sexually transmitted, but not very efficiently. Hepatitis C virus has been isolated in the semen, vaginal fluid, and saliva. Nevertheless, the risk of transmission of hepatitis C virus from an infected individual to a non-infected spouse or partner without the use of condoms over a lifetime is only about 1 to 4%. The Centers for Disease Control (CDC) and Prevention has not recommended using a barrier technique (for example, condoms) for hepatitis C virus infected individuals in a long-term monogamous relationship. On the other hand, individuals with multiple sexual partners should definitely use condoms. Furthermore, the practice of safe sex is key in preventing the transmission of other sexually transmitted diseases, such as HIV and hepatitis B.
Food, water, breast-feeding, sneezing, coughing, hugging, casual contact, or sharing eating utensils or drinking glasses have not been shown to spread hepatitis C. What's more, hepatitis C is not transmissible by kissing, unless an open wound is involved. However, to further recognize that hepatitis C is transmitted through blood, the sharing of razors and toothbrushes should be avoided.
Interestingly, the CDC has not found a definite association between tattoos and the transmission of hepatitis C virus. It is critical, nevertheless, that appropriate precautions be taken in applying tattoos, including the artist wearing gloves and using disposable equipment. In contrast to hepatitis B, the transmission of hepatitis C from the mother to the newborn around the time of delivery is unusual.
Hepatitis C virus infection can also be acquired through occupational exposures. Thus, health care workers in contact with contaminated bloods, fluids, and needles are at an increased risk for hepatitis C virus. The risk of acquiring hepatitis C virus from a needle stick involving an individual who has detectable virus in the blood is as high as 5% and about 2% on the average. The risk is higher if a hollow bore needle makes the needle stick since the potential for a greater amount of blood is higher with this type of needle. In the medical setting, patients receiving hemodialysis and medical providers in renal dialysis units have a higher frequency of hepatitis C virus infection than people in the general population.
What else can be done to prevent hepatitis C? Immune serum globulin, given after an exposure to hepatitis C virus, would not be expected to protect a susceptible individual from acquiring an hepatitis C virus infection. Moreover, no vaccine is currently available for hepatitis C virus. It should be noted, however, that hepatitis A and B vaccinations are recommended for patients who have hepatitis C virus liver disease. As already mentioned, intravenous drug abuse remains the most common mode of transmission of hepatitis C. Ideally, users should stop using drugs and enter a rehabilitation program. However, active users of drugs should not reuse or share needles, syringes, water, and other materials.
04) What are the symptoms of hepatitis C infection?
At the beginning of an hepatitis C virus infection, only about 25% of patients exhibit the characteristic symptoms of acute (rapid onset) hepatitis. These symptoms include fatigue, muscular aches, poor appetite, and low-grade fever. Rarely, yellowing of the skin and/or eyes (jaundice) also occurs. However, most patients (about 75%) experience minimal or no symptoms at the onset of hepatitis C virus.
As the hepatitis becomes chronic, most individuals remain asymptomatic (without symptoms). Indeed, many persons with chronic hepatitis C are diagnosed while undergoing routine blood work for unrelated purposes. Infected individuals may exhibit no symptoms despite progressive liver inflammation, necrosis (death of liver cells), and fibrosis (scarring). Other patients may experience chronic or intermittent fatigue and a diminished sense of well-being as a result of advancing disease. On the other hand, fatigue has been described in some individuals with relatively mild disease.
With the subsequent development of cirrhosis of the liver (more advanced scarring), hepatitis C virus patients can have muscle wasting, generalized weakness, and easy bruising. Later symptoms, which are due to the complications of cirrhosis, include fluid retention, which leads to edema (swelling of the lower extremities) or ascites (fluid in the abdominal cavity), internal bleeding (usually from dilated esophageal veins called varices), and mental confusion or sleepiness (due to hepatic encephalopathy). Another complication of hepatitis C virus cirrhosis is cancer of the liver (hepatocellular carcinoma or hepatoma), which can cause abdominal pain, weight loss, and fever.
What conditions outside the liver are associated with hepatitis C?
Several extra-hepatic (outside of the liver) conditions are associated with chronic hepatitis C. These conditions are not very common and their occurrence does not correlate with the severity of the underlying liver disease. The most widely described associated condition is cryoglobulinemia. This condition is due to the presence of abnormal antibodies (called cryoglobulins) that come from hepatitis C virus stimulation of lymphocytes (white blood cells). These antibodies can deposit in small blood vessels, thereby causing inflammation of the vessels (vasculitis) in tissues throughout the body. For example, the skin, joints, and kidneys (glomerulonephritis) may be involved.
Patients with cryoglobulinemia can have quite a variety of symptoms. These symptoms may include weakness, joint pain or swelling (arthralgia or arthritis), a raised, purple skin rash (palpable purpura) usually in the lower portion of the legs, swelling of the legs and feet due to loss of protein in the urine from the kidney involvement, and nerve pain (neuropathy). In addition, these patients may develop Raynaud's phenomenon, in which the fingers and toes turn color (white, then purple, then red) and become painful in cold temperatures.
The diagnosis of cryoglobulinemia is made by doing a special test in the laboratory to detect the cryoglobulins in the blood. In this test, the cryoglobulins are identified when the blood sample is exposed to the cold (cryo means cold). In addition, a finding of typical inflammation of small blood vessels in certain tissue biopsies (e.g., the skin or kidney) supports the diagnosis of cryoglobulinemia. All of the symptoms of cryoglobulinemia often resolve with successful treatment of the hepatitis C virus infection.
B-cell non-Hodgkin's lymphoma, a cancer of the lymph tissue, has also been associated with chronic hepatitis C virus. The cause is thought to be the excessive stimulation by the hepatitis C virus of B-lymphocytes, which results in the abnormal reproduction of the lymphocytes. Interestingly, the disappearance (remission) of an hepatitis C virus-associated low-grade (not very active) non-Hodgkin's lymphoma has been reported with interferon therapy. Most individuals with hepatitis C virus-associated high-grade non-Hodgkin's lymphoma, however, will require the usual anti-cancer therapies.
Two skin conditions, lichen planus and porphyria cutanea tarda, have been associated with chronic hepatitis C virus. It is important to know that both of these skin conditions can resolve with successful interferon therapy for the hepatitis C virus. In addition, up to 25% of hepatitis C virus patients have autoimmune antibodies (against one's own proteins), such as anti-nuclear antibody, anti-smooth muscle antibodies, and rheumatoid factor.
05) What is the usual progression of chronic infection with hepatitis C virus?
Our understanding of the natural progression (history) of hepatitis C infection is still evolving. About 15% of patients with acute hepatitis C virus infection spontaneously recover (clear the virus). Eighty five percent, however, develop chronic liver disease. How many of these patients progress to cirrhosis of the liver? Is there a way to predict who will develop cirrhosis? And then, how many will develop liver failure, including the complications of cirrhosis, or liver cancer? Once a person has cirrhosis, how long is he/she expected to live? These are very pertinent questions for which there are no clear-cut answers, only reasonable estimates.
There are several ways to examine the natural history of chronic hepatitis C infection; retrospective (looking back in time), prospective (looking forward), or combined retrospective/prospective studies. A retrospective study involves identifying patients with established chronic hepatitis C infection and correlating their current stage of liver disease to the duration of their infection. Several such investigations have suggested that after acquiring hepatitis C virus, it takes about 10 to14 years for biopsy evidence of chronic hepatitis to appear, about 20 years to develop cirrhosis, and about 28 years to develop liver cancer.
There are problems with retrospective studies, however. For example, retrospective studies are inclined (biased) to select chronic hepatitis C patients who have symptoms, which is the reason the patients sought medical attention. Accordingly, information about the actual duration of infection in these patients may be inaccurate, that is, underestimated. Furthermore, retrospective studies do not tell what proportion of patients with chronic hepatitis C virus will develop cirrhosis, liver failure, or HCC.
In a prospective study, an entire group of hepatitis C patients are followed from the time they first become infected. These studies have necessarily involved patients who received contaminated blood, since in these individuals, the time of acquisition of hepatitis C virus can be accurately determined. However, the follow-up in most of these studies is relatively short. Furthermore, since some of these patients are being treated with antiviral therapy, the natural progression of the disease may be modified by the treatment. Anyway, these prospective studies suggest that about 10 to 25% of patients develop cirrhosis within a 10 to 15 year follow-up. Moreover, only about 10% of patients develop symptoms related to their liver disease.
Retrospective/prospective studies involve identifying a group of patients who were exposed to hepatitis C virus many years ago, accounting for almost all of these patients, and then following them prospectively. The advantage of these studies is that there is a head start to the follow-up as compared to a prospective study. These retrospective studies confirm that the natural progression of chronic hepatitis C virus is quite slow and in general, complications develop over decades, not years.
Again, these retrospective/prospective studies have involved patients who were exposed to contaminated blood or blood products (such as immunoglobulin). On average, these studies have looked at patients who were exposed over twenty years ago. In two studies involving women who acquired chronic hepatitis C virus after receiving contaminated immunoglobulin over 20 years ago, less than 3% of the patients developed cirrhosis. The vast majority of patients had only mild inflammation and no fibrosis (scarring) of the liver. About one third of patients had aminotransferase (liver enzyme) levels over 100 U/L (2 to 3 times normal) and one third had normal liver tests. However, one quarter of the patients reported fatigue.
According to these retrospective/prospective studies, once cirrhosis is established, the risk of developing liver failure, that is, the complications of cirrhosis, is about 10% per year. These complications include bleeding from varices (dilated veins, usually in the esophagus), ascites (fluid in the abdomen), encephalopathy (confusion), and jaundice. The risk of developing liver cancer in a cirrhotic patient with hepatitis C virus is 1.4% per year. However, patients who have cirrhosis without complications (compensated cirrhosis) have an 80% likelihood of surviving 10 years. On the other hand, patients who have cirrhosis with complications (referred to either as decompensated cirrhosis or liver failure) have a much lower likelihood of survival, less than 50% at 5 years.
It is unclear which factors promote the progression of chronic liver disease in hepatitis C virus infection. Earlier studies suggested that individuals infected with genotype 1b may develop more serious disease, but these findings could not be substantiated. Moreover, as previously mentioned, the level of virus in the blood does not correlate with disease severity. What is clear, however, is that the regular use of alcohol, even in moderation, is detrimental in hepatitis C virus chronic liver disease.
06) Who is at high risk and should be tested for hepatitis C infection?
The Centers for Disease Control and Prevention recommend that certain people who are at high risk for hepatitis C infection should undergo testing for hepatitis C virus. These include individuals who:
Have been notified that they received a blood transfusion from a donor who later tested positive for hepatitis C
Injected illegal drugs, even if they experimented only a few times many years ago
Received a blood transfusion or solid organ transplant before July, 1992
Received a blood product for clotting problems that was produced before 1987
Have ever been on long term kidney dialysis (filtering blood to treat kidney failure)
Have evidence of liver disease (e.g., persistently abnormal ALT levels)
Guidelines for hepatitis C virus testing are less clear in certain other people who may also be at increased risk of acquiring hepatitis C virus. These include individuals who:
Are recipients of transplanted tissue (e.g., cornea, skin, heart, kidney)
Used intranasal cocaine and other non-injecting illegal drugs
Have had tattoos and/or body piercing
Have had multiple sex partners or a history of sexually transmitted disease
*Are long term steady sex partners of an hepatitis C virus positive person*
*The National Institutes of Health Consensus Development Conference recommends that these persons be tested.
What are the diagnostic tests for hepatitis C virus and how are they used to diagnose hepatitis C virus infection?
A number of diagnostic tests are currently available for hepatitis C virus. They are categorized below according to the function of the specific tests.
What about screening tests?
Screening tests are done to determine the presence of antibodies to hepatitis C virus in the blood. The enzyme immunosorbent assay (EIA) is the conventional, initial screening test to diagnose hepatitis C infection. The EIA measures specific antibodies to small pieces of the hepatitis C virus proteins (antigens). This test, therefore, is referred to as the anti-hepatitis C virus antibody test. Patients who have elevated liver enzymes (ALT/AST) and/or any of the risk factors for hepatitis C virus can be diagnosed to have hepatitis C virus with a greater than 95% certainty when the EIA is positive.
On the other hand, certain patients whose immune systems are impaired (suppressed) may not have detectable anti-hepatitis C virus antibodies even if they are actually infected with hepatitis C virus. Such immunosuppressed patients include those who are on renal dialysis, suffer from cancer and are receiving chemotherapy (drugs to kill cancer cells), or have active HIV infection. These patients cannot produce enough anti-hepatitis C virus antibodies necessary to generate a positive EIA test.
When there is a low likelihood (risk) of hepatitis C infection, individuals who test positive for hepatitis C by EIA should undergo confirmatory testing using a specialized assay that likewise tests for antibodies against the hepatitis C virus proteins. This assay is called the Recombinant Immunoblot Assay (RIBA).
Both the EIA and RIBA tests, however, do not distinguish among acute, chronic, and resolved hepatitis C virus infections because the anti-hepatitis C virus antibodies are in the blood in all three of these situations. Although EIA and RIBA are tests that measure antibodies against hepatitis C virus, these antibodies do not confer protection to the patient against acquiring hepatitis C virus. Rather, they only indicate exposure of the patient to the virus.
What are molecular tests for hepatitis C virus?
As previously described, hepatitis C virus is an RNA virus. The code of the genetic material, hepatitis C virus RNA, is unique to this virus. Several types of tests (assays) are available to measure the hepatitis C virus RNA in a person's blood. These tests are referred to as molecular tests because they examine the virus at the molecular level. The two most common systems for measuring hepatitis C virus RNA are the reverse transcription polymerase chain reaction (RT-PCR) assay and the branched chain DNA (bDNA) assay. Recently, a third type of assay, called transcription-mediated amplification (TMA), has been released.
First of all, it is important to put in perspective the relative amount of virus in an individual infected with hepatitis C virus as compared to some other types of chronic viral infection. The average number of virus particles/milliliter of blood in an individual with chronic hepatitis C virus is hundreds of thousands to several million. In contrast, someone with active hepatitis B infection has several hundred million to billions of copies (virus particles) per milliliter of blood. The relatively low concentration of the hepatitis C virus in the blood is one of the reasons it took so long for scientists to characterize the hepatitis C virus.
RT-PCR is a very powerful tool for detecting relatively low amounts of genetic material (RNA or DNA). The basis of this technique is the amplification of a target piece of nucleic acid several million times so that this target becomes measurable. Due to the extreme sensitivity of this technique, however, the slightest contamination can lead to a false positive result. On the other hand, RNA is relatively unstable (degrades easily), so that blood and tissue samples need to be handled with special precautions. If not, this instability would lead to a false negative result, that is, a negative result in someone who has hepatitis C virus.
In the early 1990's, each laboratory had its own in-house technique for the RT-PCR assay and the reliability of these assays was quite variable. Even as of now, the FDA has not approved any of the RT-PCR assays. However, most laboratories currently use one of the several available diagnostic kits that are automated and designed to reduce the likelihood of contamination. There are two types of RT-PCR, qualitative and quantitative. Qualitative hepatitis C virus RT-PCR provides the greatest sensitivity, meaning that it can measure as few as 100 copies (viral particles) of hepatitis C virus/ml of serum. As the name implies, however, qualitative RT-PCR provides only a positive (presence of hepatitis C virus) or negative (absence of hepatitis C virus) result.
By contrast, quantitative RT-PCR measures the amount of virus. These tests, however, are only accurate within a certain range of viremia (circulating virus in the blood). This means that quantitative assays are not as sensitive as qualitative assays and can only detect as few as 500 copies/ml. Moreover, these assays are less accurate at extremely high viral levels (over 2 million copies/ml). In the past year, there has been an attempt to standardize these various quantitative assays so that the levels of virus that are measured by different assays can be compared. As a matter of fact, results of quantitative RT-PCR are now reported in standard International Units/ml (IU/ml).
Branched chain DNA (bDNA) is the other quantitative technique. It is based on the amplification of the detection signal rather than of the nucleic acid itself. As a result, this test is less prone to contamination and is more accurate when measuring higher levels of the virus as compared to RT-PCR. However, the bDNA assay is not as sensitive as the RT-PCR and is unable to measure levels of virus below 200,000 copies/ml.
Finally, transcription mediated amplification (TMA) is a qualitative technique that is distinct from PCR. This test can measure as few as 2 to 5 copies of virus/ml.
What is the role of the qualitative molecular tests?
Qualitative RT-PCR is a useful test in determining whether or not a patient has circulating virus in the blood (viremia). Hence, it can be used to confirm that a reactive (positive) anti-hepatitis C virus result reflects active hepatitis C virus infection. However, confirmatory testing is usually not necessary in someone who tested reactive (positive) for anti-hepatitis C virus and also has risk factors and abnormal liver tests. In this situation, the RT-PCR most certainly would be positive. On the other hand, an individual who is anti-hepatitis C virus reactive and has risk factors but normal liver tests should undergo confirmatory testing with RT-PCR. This person may have cleared the viral infection some time ago, leaving the anti-hepatitis C virus as a marker of past exposure.
Qualitative hepatitis C virus RNA testing should also be done in individuals who may have been recently exposed to hepatitis C. Hepatitis C virus RNA is more sensitive (that is, will detect more cases) than the conventional anti-hepatitis C virus (EIA) testing in this setting. The reason for this greater sensitivity is that it may take a person as many as six to eight weeks after exposure to hepatitis C virus to develop the antibodies, whereas hepatitis C virus RNA becomes detectable five to ten days after exposure. Finally, qualitative hepatitis C virus RNA testing may be helpful to assess the patient's virologic response at certain time points during antiviral therapy (see treatment of hepatitis C virus below).
How are the results of the hepatitis C virus tests interpreted?
The table provides guidelines for interpreting the results of testing for anti-hepatitis C virus by EIA and RIBA and for hepatitis C virus RNA by qualitative RT-PCR or TMA.
Anti-HCV (EIA) Anti-HCV (RIBA) HCV RNA
(Qualitative RT-
PCR or TMA) Interpretation
Non-reactive Non-reactive Undetectable No present or past infection
Reactive Non-reactive Undetectable False positive EIA; no present or past infection
Reactive Undeterminate Undetectable In the absence of risk factors, probable false positive EIA
Reactive Positive Undetectable Probable past exposure with clearance of infection. Qualitative RNA testing should be repeated to exclude fluctuating low levels of viremia
Reactive Positive Detectable Ongoing infection
Non-reactive Non-reactive Detectable Acute HCV infection or chronic HCV infection in an immunocompromised person unable to make adequate antibodies
What is the role of quantitative hepatitis C virus RNA testing?
It should be noted that a single quantitative measurement of the level of hepatitis C virus in the blood (viral load) does not correlate with the severity of hepatitis C virus liver disease. Moreover, the viral load fluctuates in a given infected individual, although the variation is usually insignificant, that is, less than a log-fold (ten times) difference. So, there is no practical value in quantitatively measuring viral loads in patients who are not undergoing treatment.
Quantitative hepatitis C virus RNA measurements are pertinent, however, in patients who are being considered for antiviral therapy or who are being monitored during therapy. For example, patients with hepatitis C virus RNA initial levels of greater than 2 millioncopies/ml(>800,000IU/ml) are less likely to have a sustained response to conventional interferon alone or to combined interferon and ribavirin therapy. What is more, patients who experience less than a 100-fold (2-log) drop in the viral load after 12 weeks of pegylated interferon therapy are also unlikely to have a sustained response.
What tests identify the virus genotypes?
PCR assays of nucleic acids are available to determine the hepatitis C virus genotype. In some instances, the purpose of obtaining genotype information is to tailor the duration of antiviral therapy. Thus, patients with genotype 2 or 3 can be treated with a six-month course of Rebetron combination therapy (see treatment of hepatitis C virus below) instead of the conventional twelve-month course for patients infected with genotype 1. Furthermore, patients infected with genotype 2 or 3 are more likely to respond to interferon therapy than those with genotype 1. Thus, knowledge of the genotype may be useful in predicting the likelihood of a favorable response to interferon therapy.
in the US. It is the sixth leading cause of death.