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Hepatitis C Virus
Hepatitis C virus (HCV) remains one of the most consequential bloodborne pathogens encountered in clinical laboratories. Despite the availability of curative antivirals, HCV continues to drive chronic liver disease, hepatocellular carcinoma, and liver-related mortality worldwide. Understanding the pathobiology of the virus, the scope of disease, and the natural history of infection is central to supporting accurate diagnosis and effective public health response.
The Global Burden of HCV
The World Health Organization (WHO) estimates that more than 50 million people are living with chronic Hepatitis C Virus (HCV) infection, with 1 million new cases every year.1 While >95% of individuals with the disease can be cured with direct-acting antiviral (DAA) medications, each year more than 240,000 individuals, globally, die from HCV-related disorders, primarily from cirrhosis and hepatocellular carcinoma.1
The global burden is not evenly distributed. Regions with limited access to screening, safe injection practices, and antiviral therapy bear the highest prevalence and mortality, particularly parts of the Eastern Mediterranean, South‑East Asia, and Africa.2 Even in high‑income countries, underdiagnosis remains a persistent problem, limiting the population‑level impact of curative therapy.3
HCV Biology: a persistent bloodborne virus
HCV is an enveloped virus in the Flaviviridae family. Because of its single-stranded RNA genome, HCV mutates frequently, making it easier for the virus to evade the host immune system—making it more difficult to develop an effective vaccine. Due to HCV’s unique pathobiological characteristics, HCV often persists asymptomatically in most infected individuals, creating a strong tendency toward chronic infection. The high incidence of chronic asymptomatic HCV infection promotes the spread of the virus within the population and presents challenges for timely detection of infection.
Seven genotypes and more than 60 subtypes have been identified. Globally, genotypes 1, 2, and 3 are most commonly encountered, while in the US and Europe, genotype 1 predominates.4 Some genotypes have unique clinical characteristics, which may hold prognostic information, inform patient management decisions, and be useful for tracing sources of HCV epidemics.4 For example, genotype 1 has historically been considered to be the most clinically aggressive, while genotype 3 has been associated with faster liver fibrosis progression.4–6
HCV Transmission
Transmission occurs through exposure to infected blood, most commonly via injection drug use, but also through blood transfusion, perinatal exposure or exposure during childbirth, unsafe medical procedures, and less frequently, sexual contact involving blood exposure.7
In the U.S., the most common route of HCV exposure is through sharing of needles and drug paraphernalia, but globally, transmission of HCV primarily occurs via exposure to infectious blood or body fluids that contain blood – everything from birth to an infected parent to contaminated tattoos and body piercings to inadequate sterilization of medical equipment.1,8 Prior to the 1990s, transmission often occurred during blood transfusions. However, after recognition and understanding of HCV pathobiology and the asymptomatic nature of disease, a serological test was developed in the early 1990s to test donated blood for HCV to reduce transfusion-mediated transmission9. Therefore, patients who received blood transfusions and blood components prior to 1990 were also at an increased risk of HCV infection.9
HCV Infection
Acute infection
Acute HCV infection occurs within the first six months after exposure. Most infected individuals have no symptoms, and if symptoms occur, they are typically non specific, such as fatigue or mild jaundice. Approximately 15–45% of individuals spontaneously clear the virus1 during this phase, without treatment, through effective innate and adaptive immune responses. Clearance is more common in younger individuals and those who mount strong virus specific T cell responses.1,10
Chronic infection
For the remaining 55–85%, HCV establishes chronic infection, defined by persistent viremia beyond six months.10 Chronic HCV is often clinically silent for years or decades, despite ongoing hepatic inflammation and fibrosis. This prolonged asymptomatic phase explains why many diagnoses often originate in the laboratory, rather than through symptom driven testing.
Fibrosis, cirrhosis, and complications
Once chronic infection is established, the virus continuously injures hepatocytes, driving progressive scarring of the liver.
Among individuals with chronic HCV:
- 20–30% develop cirrhosis over 25–30 years11
- Progression is faster in the presence of alcohol use, HIV coinfection, metabolic disease, or older age at infection11,12
After cirrhosis develops, the annual risk of hepatocellular carcinoma is approximately 1–5%, and the risk of hepatic decompensation increases substantially. At this stage, morbidity and mortality rise sharply, even if viral replication is later controlled.13
HCV Disease
Initially, HCV infection causes an acute, often asymptomatic disease, which in most cases, develops into chronic disease.1 The early signs and symptoms of both acute and chronic HCV infection include fatigue, poor appetite, and weight loss—vague symptoms that can easily be attributed to other causes. This lack of defined symptoms throughout disease progression has led the Centers for Disease Control and Prevention (CDC) to label Hepatitis C as a silent epidemic.14 During advanced, chronic liver disease, HCV infection may present with jaundice, causing yellowing of the eyes and skin, accompanied by dark urine and pale, clay-colored stools.15
Most acute HCV infections are asymptomatic, meaning reported cases represent only a fraction of true incidence. Because symptoms can manifest many years after initial infection and symptoms, if present, are often vague and attributed to other diseases. Many people do not realize they have an active HCV infection. Therefore, screening is important so that diagnosis and curative treatments can be started as soon as possible.
For every reported acute case, the CDC estimates that nearly 14 additional infections go undetected,16 reinforcing the lab’s role in identifying HCV infection through screening and reflex testing strategies.
Laboratory Diagnosis
Getting tested is the best way to know if you have HCV—early detection can lead to early treatment, which can lead to cure in 95% of patients. With the advent of rapid tests and point-of-care tests to detect the presence of HCV antibodies using a simple blood draw, testing availability has improved accessibility to HCV screening and diagnosis. The CDC recommended that adults, regardless of risk factors, are tested at least once in their lifetime.17 Individuals with risk factors—including those with HIV, prior drug use, transplant recipients, and children of HCV-positive mothers—should receive testing at regular intervals. Those with ongoing risk factors should be routinely tested at a higher frequency. Further, the CDC states that anyone who asks for a test, regardless of risk factors, should receive it in an ongoing effort to destigmatize the disease.17
Detection and diagnosis of HCV infection typically follow a diagnostic algorithm. The initial testing is a serologic test, often detecting total antibodies (IgM and IgG) developed in response to HCV infection. Those with non-reactive results are generally considered negative for HCV. Patients with reactive anti-HCV antibody results are considered presumptive positive for HCV infection and the sample is reflexed to a quantitative viral load test, often a real-time reverse transcriptase PCR, to confirm diagnosis of active HCV infection. Confirmation of serological reactive results with a viral load test is critical to distinguish between current and past HCV infection. Those with a detectable viral load are confirmed to have an active HCV infection, and the viral load results establish a baseline for treatment monitoring.
Most testing today continues to follow the HCV testing algorithm. However, in high-risk patients or those with recent HCV exposure who have not yet developed an antibody response, qualitative molecular tests, some that are available at the point-of-care, are often used as the initial test for diagnosis. The use of multiple testing strategies and increasing accessibility of HCV testing in the population is vital to reach the goal of HCV elimination.18
Along with HCV-specific testing, other laboratory tests are often ordered and can provide additional context to interpretation of HCV test results. These may include liver enzyme function tests (e.g., AST and ALT), complete blood count, renal function tests, and other infectious disease testing, such as HBV, HAV, and HIV.
Treatment
While there is no vaccine for Hepatitis C, there are medications that can treat—and even cure—infection.
In patients with detectable viral load and active HCV infection, Direct Acting Antivirals (DAAs) are prescribed. DAAs target essential viral replication processes, thereby inhibiting viral replication. DAA treatments work in 95% of HCV patients and often result in complete cure of HCV infection. There are many medications approved to treat HCV. Some of the original DAAs were genotype-specific, requiring testing to confirm the genotype to prescribe the appropriate DAA, along with other relevant medical history.1,7,19 HCV genotype testing is available in some clinical laboratories to determine the genotype present and aid in DAA-therapy decisions. However, newer DAAs available can treat multiple genotypes, some being “pan-genotype,” reducing the need for genotype testing and decreasing the time from diagnosis and initiation of active treatment.
How advancing clinical capabilities can help in the laboratory (and beyond)
HCV remains a disease where laboratory detection defines the clinical pathway. Most infected individuals feel fine and show normal liver enzyme levels, but the disease is silently progressing. Serologic screening, confirmatory RNA testing, and appropriate interpretation of results directly influence whether infection is identified early or missed.
From a public health perspective, laboratories also anchor surveillance systems. Reported cases feed national estimates of disease burden and shape elimination strategies. From a patient perspective, a single accurate result can divert decades of liver injury.
Bottom line
Hepatitis C is no longer an untreatable disease, but it remains a widely prevalent, frequently under-diagnosed infection with severe life altering consequences. When the stakes are this high, diagnostic testing has to be trustworthy. With sensitive, precise, and accurate testing, laboratorians and care teams can be confident in the diagnoses they support
Silence is the virus’s greatest advantage. The lab is often the first—and only—place where that silence is broken.
