What is the normal range for Hep B Surf Ab Quant?

The standard protective threshold is ≥10 mIU/mL, as defined by the CDC and WHO. Most labs report results below 10 mIU/mL as low or non-immune. The HealthMatters optimal range for this test is 9.9–1000 mIU/mL.

Why does my portal say "patient does not have immunity to hepatitis B virus"?

This is an interpretive comment added by some labs when the anti-HBs level is below 10 mIU/mL. It does not mean you have hepatitis B — it means your antibody level is currently below the protective threshold. Vaccination or a booster dose is typically the next step.

Why would my hep B antibodies be low after vaccination?

Hepatitis B antibody levels naturally decline over time — this is expected and does not mean the vaccine failed. Immune memory is preserved even when circulating antibody falls below 10 mIU/mL. A single booster dose usually restores a protective level. Age, immunosuppression, obesity, and smoking are all associated with lower vaccine responses.

Does a low result mean I have hepatitis B?

No. A low hepatitis B surface antibody result means you lack sufficient protective antibodies — not that you are infected. To check for active or past infection, your doctor would order different tests: hepatitis B surface antigen (HBsAg) to detect active infection, and hepatitis B core antibody (anti-HBc) to detect past exposure.

What is a protective level of hepatitis B surface antibody?

A level of ≥10 mIU/mL is the internationally accepted protective threshold, based on CDC and WHO guidelines. Levels above 100 mIU/mL are considered strongly protective with a longer expected duration before waning.

Hep B Surf Ab Quant Low: What Your Result Means

Serum

Other names: Hep B Surf Ab Quant, Hepatitis B Surface Ab QN, Hepatitis B Surface Antibody Quantitative, Hepatitis B Surf Ab Quant, Hepatitis B Surface Ab Immunity QN, Hep B Surface Ab Quant, HBsAb Quantitative, Anti-HBs Quantitative, Hepatitis B Surface Antibody Immunity Quantitative, Hep B Surf Ab QN, Hepatitis B Surface Ab Quantitative, HBsAb QN, Hep B Surface Ab QN, Anti-HBs, HBsAb, Hep B Surf Ab, Hepatitis B Surface Antibody QN, Hep Bs Ab Quant, Hepatitis B Surface Ab QN Low, Hepatitis B Surf Ab Immunity QN, HBV Surface Antibody Quantitative

Optimal Result: 9.9 - 1000 mIU/ml.

Infectious Disease Profile

From Healthmatters.io Team and reviewed by HM Editorial Team

Written on April 22, 2026 | Last updated Updated on April 22, 2026

Lab Results Explained and Tracked

The Hepatitis B Surface Antibody Quantitative test measures the level of hepatitis B surface antibodies (anti-HBs) in your blood in mIU/mL (milli-International Units per milliliter). It may appear on your lab report as Hep B Surf Ab Quant, Hepatitis B Surface Ab, QN, or Hepatitis B Surface Ab Immunity, QN.

This level tells you whether you have sufficient immunity against hepatitis B virus (HBV), either from vaccination or past infection. A result flagged as low means your antibody level is below the protective threshold of 10 mIU/mL — the standard cutoff used by the CDC, WHO, and most clinical guidelines to define immunity. It does not mean you have hepatitis B; it means your current antibody level is not considered sufficient to protect against infection.

At a Glance

The protective threshold for hepatitis B surface antibody is ≥10 mIU/mL
A result below 10 mIU/mL is considered non-immune — insufficient protection against HBV
The most common cause is waning immunity after vaccination — a normal decline in antibody levels over time
The specific values <3.5 and <3.1 are LabCorp reporting thresholds, not your actual measured values — they mean antibodies were undetectable on that assay
A low result does not mean you currently have hepatitis B — further testing would be needed to determine that
If you are a healthcare worker or at ongoing exposure risk, a level below 10 mIU/mL should be treated as non-immune and addressed promptly
Next steps typically involve hepatitis B vaccination or a booster dose

What does "Hep B Surf Ab Quant Low" mean?

A low result means the quantitative level of anti-HBs antibodies in your blood was below 10 mIU/mL — the level considered protective against hepatitis B infection. The result is reported as low because it falls below the laboratory's reference range.

The most common cause is waning immunity after vaccination — a normal decline in antibody levels over time. This does not necessarily mean you are unprotected: immune memory cells can still mount a rapid response to a booster dose or real exposure even when circulating antibody is low. For clinical purposes, however, a level below 10 mIU/mL is treated as non-immune and vaccination is usually recommended.

Other reasons for a low result include never having been vaccinated, being a vaccine non-responder (a small proportion of people do not develop adequate antibody after a standard vaccine series), or being immunocompromised.

What do Hep B Surf Ab Quant 3.5, 3.1, or values with "<" mean?

If your result shows <3.5 mIU/mL, <3.1 mIU/mL, or a similar value prefixed with "<", this is a LabCorp reporting convention — not an actual measured antibody level. It means hepatitis B surface antibodies were below the lower limit of quantification for the assay. LabCorp uses 3.5 mIU/mL as the detection floor on one assay and 3.1 mIU/mL on another. The "<" symbol means "less than" this limit.

In all of these cases, antibodies were not detected at a quantifiable level — equivalent to a negative or non-immune result, and well below the protective threshold of 10 mIU/mL. The clinical meaning is identical regardless of whether your report shows <3.5, <3.1, or any similar below-limit value.

Understanding the reference range

Result	Interpretation
≥10 mIU/mL	Protective — sufficient immunity against hepatitis B
5–9.9 mIU/mL	Borderline — may warrant repeat testing or a booster dose (often reported as low)
<5 mIU/mL	Non-immune — no meaningful antibody protection detected (often reported as negative or low)
<3.5 or <3.1 mIU/mL	LabCorp below-limit-of-detection reporting — equivalent to non-immune

The 10 mIU/mL threshold is the internationally accepted minimum protective level defined by the CDC and WHO. Some laboratories use 12 mIU/mL as their cutoff — always refer to your specific lab's reference range. The HealthMatters optimal range for this test is set at 9.9–1000 mIU/mL, consistent with clinical guidelines.

What is "Hepatitis B Surface Ab Immunity, QN"?

This is a LabCorp test name variant for the same quantitative anti-HBs test. "Immunity" reflects its purpose — assessing hepatitis B immune status. "QN" means quantitative, indicating the result is a number in mIU/mL rather than just reactive or non-reactive. A low result on this test carries the same clinical meaning as described above.

Why does my portal say "Warning Low" or "Patient does not have immunity to hepatitis B virus"?

It does not mean you have hepatitis B — it means your current antibody level is below the protective threshold. "Warning Low" or "WarningLow Hepatitis B Surf Ab Quant" is a standard lab flag for any result below the reference range. The phrase "patient does not have immunity to hepatitis B virus" is an interpretive comment added by some labs and portals to clarify the significance of a sub-threshold result. Vaccination or a booster dose is typically the next step.

What are the next steps after a low result?

If you have been vaccinated previously: A low result after vaccination usually means antibody levels have declined over time — a normal pattern. A single booster dose is often sufficient to restore a protective level. Your doctor will determine whether a booster or a full re-vaccination series is appropriate based on your vaccination history.

If you have never been vaccinated: A primary hepatitis B vaccine series (three doses over six months) is recommended. Testing after completing the series confirms that a protective level has been achieved.

If you are a vaccine non-responder: A small proportion of people — roughly 5–10% of healthy adults — do not develop adequate antibody after a standard vaccine series. A repeat series is usually tried; those who still do not respond are considered non-responders. This reflects individual immune variation, not a harmful effect of the vaccine. Non-responders in high-risk settings require specific management guidance from their doctor.

If you are a healthcare worker or at ongoing exposure risk: A level below 10 mIU/mL should be treated as non-immune and addressed promptly. The CDC recommends that healthcare workers who do not achieve ≥10 mIU/mL after two full vaccine series be counselled on susceptibility and the need for post-exposure prophylaxis if an exposure occurs.

FAQ about Hepatitis B Surf Ab Quant

What does "Hep B Surf Ab Quant Low" mean?

It means your hepatitis B surface antibody level is below 10 mIU/mL — the threshold considered protective against hepatitis B. In most cases this reflects normal post-vaccination decline, not active infection or illness. It does not mean you have hepatitis B.
What do Hep B Surf Ab Quant 3.5, 3.1, or values with "<" mean?

These are LabCorp reporting conventions indicating hepatitis B surface antibodies were below the assay's lower limit of quantification — 3.5 mIU/mL on one assay, 3.1 mIU/mL on another. The "<" symbol means "less than" this limit. In all cases, antibodies were not detected at a quantifiable level, which is equivalent to a negative or non-immune result.
What is the normal range for Hep B Surf Ab Quant?

The standard protective threshold is ≥10 mIU/mL, as defined by the CDC and WHO. Most labs report results below 10 mIU/mL as low or non-immune. The HealthMatters optimal range for this test is 9.9–1000 mIU/mL.
What is "Hepatitis B Surface Ab Immunity, QN"?

A LabCorp test name for the same quantitative hepatitis B surface antibody test. "Immunity" reflects its purpose — assessing hepatitis B immune status. "QN" means quantitative, so the result is a number in mIU/mL rather than just positive or negative.
Why does my portal say "patient does not have immunity to hepatitis B virus"?

This is an interpretive comment added by some labs when the anti-HBs level is below 10 mIU/mL. It does not mean you have hepatitis B — it means your antibody level is currently below the protective threshold. Vaccination or a booster dose is typically the next step.
Why would my hep B antibodies be low after vaccination?

Hepatitis B antibody levels naturally decline over time — this is expected and does not mean the vaccine failed. Immune memory is preserved even when circulating antibody falls below 10 mIU/mL. A single booster dose usually restores a protective level. Age, immunosuppression, obesity, and smoking are all associated with lower vaccine responses.
Does a low result mean I have hepatitis B?

No. A low hepatitis B surface antibody result means you lack sufficient protective antibodies — not that you are infected. To check for active or past infection, your doctor would order different tests: hepatitis B surface antigen (HBsAg) to detect active infection, and hepatitis B core antibody (anti-HBc) to detect past exposure.
What is a protective level of hepatitis B surface antibody?

A level of ≥10 mIU/mL is the internationally accepted protective threshold, based on CDC and WHO guidelines. Levels above 100 mIU/mL are considered strongly protective with a longer expected duration before waning.

Lab Results Explained and Tracked

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What does it mean if your Hepatitis B Surf Ab Quant result is too high?

A high or protective Hepatitis B Surface Antibody Quantitative result (≥10 mIU/mL) means you have sufficient immunity against hepatitis B virus — either from vaccination or recovery from past infection. Most guidelines consider any value ≥10 mIU/mL to be protective, and no action is typically needed. Antibody levels naturally decline over time, so periodic retesting may be appropriate in certain high-risk settings.

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What does it mean if your Hepatitis B Surf Ab Quant result is too low?

A low Hepatitis B Surface Antibody Quantitative result means your anti-HBs level is below 10 mIU/mL — the protective threshold for hepatitis B immunity. This indicates your current antibody level is not sufficient to protect against infection.

In most cases, this reflects normal post-vaccination decline. It does not mean you currently have hepatitis B. A booster dose often restores immunity in people who were previously vaccinated. If you are a healthcare worker or at ongoing exposure risk, address this result promptly with your doctor.

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Hep B Surf Ab Quant Low: What Your Result Means

At a Glance

What does "Hep B Surf Ab Quant Low" mean?

What do Hep B Surf Ab Quant 3.5, 3.1, or values with "<" mean?

Understanding the reference range

What is "Hepatitis B Surface Ab Immunity, QN"?

Why does my portal say "Warning Low" or "Patient does not have immunity to hepatitis B virus"?

What are the next steps after a low result?

FAQ about Hepatitis B Surf Ab Quant

What does "Hep B Surf Ab Quant Low" mean?

What do Hep B Surf Ab Quant 3.5, 3.1, or values with "<" mean?

What is the normal range for Hep B Surf Ab Quant?

What is "Hepatitis B Surface Ab Immunity, QN"?

Why does my portal say "patient does not have immunity to hepatitis B virus"?

Why would my hep B antibodies be low after vaccination?

Does a low result mean I have hepatitis B?

What is a protective level of hepatitis B surface antibody?

All Your Lab Results. One Simple Dashboard.

What does it mean if your Hepatitis B Surf Ab Quant result is too high?

Related Health Conditions

All Your Lab Results. One Simple Dashboard.

Import, Track, and Share Your Lab Results Easily

Import, Track, and Share Your Lab Results

What does it mean if your Hepatitis B Surf Ab Quant result is too low?

Related Biomarkers

Article Review & Sources

Bring All Your Lab Results Together — In One Place

Gather Your Lab History — and Finally Make Sense of It

Finally, Your Lab Results Organized and Clear

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What's included in a Healthmatters membership

Import Lab Results from Any Source

See Your Health Timeline

Understand What Your Results Mean

Enter Your Lab Reports Yourself — Always Free Enter Your Lab Reports — Always Free

Visualize Your Results

Export Your Complete Lab History in a Single File Export Your Complete Lab History

Comprehensive Data Entry Service for Your Reports Data Entry Service for Your Reports

Securely Share With Anyone You Trust

Let Your Lab Results Tell the Full Story

Once your results are in one place, see the bigger picture — track trends over time, compare data side by side, export your full history, and share securely with anyone you trust.

Bring all your results together to compare, track progress, export your history, and share securely.

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