Hepatitis A IgG Test

Most people assume they're protected against hepatitis A. Maybe they were vaccinated as a child, or maybe they figure they would have gotten sick by now if they were vulnerable. But assumptions aren't immunity. In the United States, only about 24.2% of adults over age 20 had detectable antibodies against hepatitis A between 2007 and 2012, meaning roughly three out of four adults may have no protection at all.

This test answers a simple but surprisingly useful question: does your body have the antibodies needed to fight off hepatitis A if you're exposed? A positive result means you're protected, either from a past infection or a successful vaccination. A negative result means you're vulnerable, and the fix is straightforward: get vaccinated.

What This Test Tells You

Hepatitis A IgG (immunoglobulin G, the long-lasting type of antibody) is a protein made by specialized immune cells in your bone marrow and lymph tissue. After your body encounters the hepatitis A virus, whether through natural infection or vaccination, these antibodies appear in your blood and stay there for life. They're your body's permanent memory of the threat, ready to neutralize the virus if it shows up again.

Unlike many blood tests where you're looking for a number in an ideal range, this one works more like a yes-or-no switch. Either you have protective antibodies or you don't. The threshold for protection is generally considered to be 10 mIU/mL (milli-international units per milliliter, a standardized way of measuring antibody concentration). Above that line, you're considered immune. Below it, you're susceptible.

One thing this test cannot do is tell you how you became immune. A positive result looks the same whether your antibodies came from a childhood vaccine or from an infection you never knew you had. If you were naturally infected, your antibody levels will typically be 10 to 100 times higher than what vaccination produces, but both provide lasting protection.

Why Immunity Matters

Hepatitis A is a viral infection that targets the liver. It spreads through contaminated food, water, or close contact with an infected person. Unlike hepatitis B and C, it doesn't become chronic, but an acute infection can be miserable: weeks of fatigue, nausea, jaundice (yellowing of the skin and eyes), and abdominal pain. In some people, particularly those with pre-existing liver disease, it can be dangerous.

A matched study of 110 deaths and 414 controls from U.S. outbreaks between 2016 and 2019 identified who is most at risk when acute hepatitis A does strike. People with non-viral liver disease were about 5 times as likely to die. Those with a history of hepatitis B were roughly 2.4 times as likely, and people with diabetes or cardiovascular disease faced about double the mortality risk.

Who Is Still Unprotected

Immunity patterns follow age and geography in ways that might surprise you. Older adults in the U.S. are more likely to be immune because hepatitis A circulated more widely decades ago. Younger adults, especially those born between 1980 and the early 2000s, often fall into a gap: too young to have been exposed naturally, but born before universal childhood vaccination became routine in 2006.

NHANES data from 1999 to 2012 showed the lowest immunity rates, around 16% to 17.6%, among U.S. adults aged 30 to 49. A study in California found that Asian/Pacific Islanders and Hispanic adults had substantially higher immunity rates (68.2% and 63%, respectively) compared to 28.1% for White adults, reflecting different patterns of childhood exposure and travel to higher-prevalence regions.

People living with HIV face a distinct vulnerability. National survey data suggest that roughly 39% of adults with HIV may be susceptible to hepatitis A, and if they do acquire the infection, they are at increased risk for more severe disease and prolonged viral shedding.

Interpreting Your Result

The standard protective threshold is 10 mIU/mL by most commercial assays. Some researchers have proposed slightly different cutpoints, ranging from 10 to 33 mIU/mL depending on the assay used. One study found that different test platforms can give inconsistent qualitative interpretations (positive vs. negative) when antibody levels fall in the 15 to 30 mIU/mL zone. Below 10 to 15 mIU/mL, all major assays agree: you need vaccination.

The exact lower limit of antibody needed to prevent infection has not been definitively established, and it may be quite low. Immune globulin given as a preventive measure provides roughly 80% to 90% protection with very small detectable antibody levels. Because no absolute protective level has been pinpointed, most labs use their assay's detection limit as the practical threshold.

Tracking Your Trend

Unlike most biomarkers, hepatitis A IgG does not require serial monitoring. Once your immune system produces these antibodies, they persist for decades and usually for life. Long-term studies show that more than 97% of vaccinated adults remain positive for at least 20 years, and mathematical modeling predicts that 95% or more will still have detectable antibodies at 30 years, with 90% or more at 40 years.

That said, there are a few situations where rechecking makes sense. If you were vaccinated while immunocompromised (for example, after an organ transplant or during chemotherapy), your initial response may have been weaker and antibody levels can fade faster. In one study, seroconversion rates after complete vaccination ranged from 0% to 97% in transplant recipients, compared to 94% to 100% in healthy controls. If you fall into this category, a single follow-up test a few months after completing your vaccine series confirms whether you responded adequately.

For most healthy adults who test positive once, a single result is sufficient. You do not need annual retesting. The stability of this antibody over time makes it one of the few lab values where a single measurement tells you everything you need to know.

When Results Can Be Misleading

The biggest source of unreliable results is assay variability near the protective threshold. If your antibody level falls between 15 and 30 mIU/mL, different test platforms may classify the same sample as positive or negative. If you get a borderline or equivocal result, retesting with the same assay or a different platform can clarify your status.

High-dose biotin supplements (the kind sometimes marketed for hair and nail health) can interfere with certain test platforms that use a specific chemistry called streptavidin-biotin binding. In one study, biotin concentrations at or above 1,200 ng/mL produced 100% false-positive results for total hepatitis A antibody on affected assays. If you take biotin supplements, mention this to your lab or stop supplementation for at least 72 hours before testing.

Standard commercial assays may also lack the sensitivity to detect the low antibody levels that some vaccinated people maintain. A negative result after vaccination does not always mean you've lost protection entirely; your immune memory cells may still mount a rapid defense if exposed. But from a practical standpoint, if the test says negative, the safest course is to get revaccinated.