Titer Testing Guide: What Immunity Tests Measure, Thresholds, and How to Order

Educational guide · Reviewed June 2026 · By the Laboratories.org editorial team

A titer test is a blood test that measures your level of IgG antibodies to a specific disease, confirming whether prior vaccination or infection has left you immune. Nursing students, healthcare workers, and immigration applicants typically need titer results for Hepatitis B, MMR, and Varicella before starting clinical rotations or adjustment-of-status exams.

What is a titer test?

A titer test — also called an immunity test or serology test — is a blood test that measures the presence and concentration of specific antibodies in your bloodstream. The word "titer" refers to the measured level of antibodies detected. These tests reveal whether your immune system retains protection from a past vaccination or infection.

The role of IgG antibodies

The immune system produces several classes of antibodies. For immunity testing, the relevant class is IgG (Immunoglobulin G) — the most abundant and long-lasting antibody type. After exposure to a pathogen or vaccine, the immune system generates IgG antibodies targeted to that specific antigen. These IgG antibodies persist over time and serve as the body's "memory" for that pathogen.

Do not confuse IgG with IgM. IgM antibodies appear early in an active infection and indicate recent or current illness, not long-term immunity. Immunity titer tests always measure IgG, not IgM — ordering the wrong class produces meaningless results for immunity verification purposes.

Qualitative vs. quantitative titers

A quantitative titer gives the actual numerical antibody level. For example, a Hepatitis B surface antibody result might read "24.5 mIU/mL" (immune) versus "1.2 mIU/mL" (non-immune). Nursing programs, clinical training sites, and USCIS immigration exams typically require quantitative titers with the laboratory printout showing the numerical value. Getting a qualitative result when a school requires quantitative will mean the test must be redone at additional cost.

How the blood draw works

A standard venous blood draw (phlebotomy) is performed — the same as any routine blood test. No fasting is required for most titer tests. The serum is analyzed at a CLIA-certified laboratory using an ELISA (enzyme-linked immunosorbent assay), which measures how much antibody binds to a target antigen. Results are typically available within 1–5 business days, depending on the laboratory and panel ordered.

Common titers: Hep B, MMR, Varicella

Three titer panels are required by virtually every nursing, medical, PA, dental, and allied health program in the United States: Hepatitis B surface antibody, MMR (measles, mumps, rubella), and Varicella. Each tests for a different type of immunity and has its own threshold and nuances.

Hepatitis B surface antibody (HBsAb / anti-HBs)

This test detects the antibody that confers protection against the hepatitis B virus. The immune threshold is an anti-HBs level of ≥ 10 mIU/mL — the internationally recognized standard for protective immunity.

Critical ordering distinction: Schools and employers need the antibody (HBsAb or anti-HBs) test, not the hepatitis B surface antigen (HBsAg). The antigen test checks whether you are currently infected — it does not measure immunity. Ordering the wrong test is one of the most common mistakes students make.

If non-immune after a complete primary vaccine series, the CDC and Hepatitis B Foundation recommend completing a second vaccine series, preferably with a different vaccine brand (such as Heplisav-B 2-dose or PreHevbrio 3-dose). Non-responders to the first series have a 30–50% chance of responding to the second series. A small percentage of people (approximately 5–15%) do not mount a measurable antibody response to any number of vaccine doses and are classified as permanent non-responders.

MMR (Measles, Mumps, and Rubella) titers

The MMR titer tests for IgG antibodies to each of the three diseases separately — measles (rubeola), mumps (parotitis), and rubella (German measles). Results are typically reported as an index value.

Important caveat for measles: The IgG blood test for measles can produce false negatives — meaning a person is actually immune but their antibody level is not detectable. For this reason, the CDC and Immunization Action Coalition (IAC) state that documentation of two doses of MMR given on or after the first birthday, at least 28 days apart, supersedes (takes precedence over) a negative serology result. A person with two documented MMR doses does not need to be revaccinated based on a negative titer alone.

Varicella (Chickenpox) titer

This test measures IgG antibodies to the varicella-zoster virus (VZV), which causes chickenpox. A typical commercial ELISA reports results as an index value.

Important limitation: commercial VZV IgG ELISAs are reliable for detecting immunity from wild-type (natural) infection but are not sensitive enough to reliably detect seroconversion after vaccination alone. The CDC notes that routine post-vaccination serologic testing is not recommended because of this limitation. Documentation of a 2-dose varicella vaccine series is considered sufficient proof of vaccination without requiring a confirmatory titer.

For healthcare workers, being born before 1980 is considered general-population evidence of immunity, but this is not sufficient for clinical settings — the risk of spreading varicella to immunocompromised patients is too high. Provider-documented history of chickenpox (in a medical chart) counts as acceptable evidence; self-reported history does not.

What your results mean

A positive titer result indicates that the body has detectable IgG antibodies above the established protective threshold for that disease — considered laboratory evidence of immunity from either prior vaccination or natural infection. The following table summarizes all common titer tests at a glance.

An equivocal or indeterminate result falls in a borderline range. Per IAC and CDC guidance, equivocal results should be treated as non-immune — the person should receive the appropriate vaccine or booster series and re-test after waiting the proper interval.

The booster-and-retest process

When a titer comes back negative or equivocal, the standard protocol is to receive the vaccine, wait for immunity to develop, and then re-test. Skipping or shortening the waiting period is the single most common cause of false non-immune re-test results.

1. Receive the appropriate vaccine or booster for the disease with the non-immune result (see disease-specific guidance in the Common Titers section above).
2. Wait 6–8 weeks after the final vaccine dose before re-testing. Testing too soon produces a false non-immune result because vaccine antigens may still be circulating and can interfere with or mask the developing antibody response.
3. Re-test (repeat titer). If the result is now positive, the process is complete and documentation can be submitted to the school, employer, or immigration civil surgeon.
4. If still non-immune after a complete series plus booster: The person may be a vaccine non-responder. For schools and clinical sites, documentation of vaccination attempts is typically sufficient — keep all records showing the full series and subsequent non-immune titer results.
5. Hepatitis B non-responders specifically: After a second complete vaccine series (ideally with a different brand), if the anti-HBs level remains below 10 mIU/mL, the person should be tested for active HBsAg infection and receive individualized counseling about occupational exposure risk.

Who needs titers?

Titer testing is required in several well-defined situations. The core requirement is almost always proof of immunity to Hepatitis B, measles, mumps, rubella, and varicella.

Nursing, medical, and allied health students

Virtually all U.S. nursing, medical, PA, NP, dental, pharmacy, and allied health programs require proof of immunity before students can begin clinical rotations. Hospitals, clinics, and other clinical training sites set the ultimate requirements — schools must comply with what their partner sites mandate. Required titers almost universally include Hepatitis B surface antibody, MMR (as a panel), and Varicella. Some programs also require a Hepatitis A titer or documentation. Schools typically require quantitative titers with numerical values, not qualitative results.

Healthcare workers

Hospitals, long-term care facilities, outpatient clinics, and other healthcare employers require new-hire employees to document immunity. OSHA's Bloodborne Pathogen Standard requires employers to offer Hepatitis B vaccination to at-risk workers and provide post-vaccination antibody testing as indicated. Workers who decline must sign a formal declination form. The CDC recommends that healthcare personnel demonstrate evidence of immunity to measles, mumps, rubella, and varicella — either via documented two-dose vaccine series or positive titer. Annual TB testing is no longer recommended for healthcare workers unless there is a known exposure or documented ongoing transmission at the facility.

Immigration (Form I-693)

U.S. Citizenship and Immigration Services Form I-693 — the Report of Immigration Medical Examination and Vaccination Record — requires applicants for adjustment of status to show proof of age-appropriate vaccinations or immunity. A USCIS-designated civil surgeon performs the exam. Laboratory evidence of immunity (titer) is an acceptable substitute for vaccination records for measles, mumps, rubella, Hepatitis A, Hepatitis B, Varicella, and Polio (titers must cover all three poliovirus types). Tests must use FDA-approved or CLIA-certified kits. Self-reported vaccine history without written documentation is not acceptable.

Other contexts

Certain occupations outside healthcare may also require titers: veterinary staff, childcare workers, laboratory personnel, military personnel, first responders, and staff at correctional facilities or homeless shelters. International travel-medicine requirements may also trigger titer testing for specific destinations.

Titers vs. vaccination records

Both documented vaccination records and a positive titer can serve as acceptable evidence of immunity in most contexts. But many schools, hospitals, and clinical sites specifically require titers, or accept titers in lieu of records, for several practical reasons.

• Records are lost or unavailable. Adults born in other countries, those who changed providers, or those whose childhood records were lost cannot produce historical vaccination cards. A titer establishes current immunity without needing those records — particularly important for immigrants or international students.
• Vaccination does not always mean immunity. A small percentage of vaccinated people are primary non-responders — they received the shots but never mounted a detectable immune response. Some individuals' vaccine-induced immunity wanes over years. A titer directly measures the result of vaccination (the antibody level) rather than the act of vaccination itself.
• Healthcare settings have higher standards. Healthcare workers interact with immunocompromised, elderly, newborn, and other high-risk patients. OSHA, The Joint Commission, and hospital accreditation bodies expect documented proof of immunity — not just proof of vaccination attempt.

When vaccination records supersede titers: Per the IAC and CDC, documentation of two doses of MMR given on or after the first birthday, separated by at least 28 days, is considered proof of measles immunity and supersedes serologic testing results. In other words, if a person has two documented MMR doses, a negative measles titer does not require revaccination. The same logic applies to varicella: a documented 2-dose varicella vaccine series supersedes a negative serology result.

TB testing context

TB testing is not an antibody titer — it measures the immune system's response to tuberculosis bacteria exposure, not immunity from vaccination. However, it is nearly always required alongside titer panels for healthcare students, healthcare workers, and immigration exams.

Per CDC's 2019 updated guidelines, all U.S. healthcare workers should be screened for TB at baseline (upon hire). Baseline screening includes an individual TB risk assessment, TB symptom evaluation, and a TB test. Annual TB testing is no longer recommended for healthcare workers unless there is a known exposure event or documented ongoing TB transmission at the facility. The CDC and major professional societies prefer the IGRA blood test for BCG-vaccinated individuals to avoid false positives from BCG cross-reactivity.

A positive TB test does not diagnose active TB disease — it indicates the person has been infected with TB bacteria at some point (latent TB infection, LTBI). A positive result triggers follow-up evaluation: chest X-ray and clinical assessment to rule out active TB disease. Most people with LTBI are not contagious and will never develop active TB.

How to order online

Individuals can order titer tests without a doctor's visit through direct-to-consumer laboratory platforms. Both major national lab networks — Labcorp and Quest Diagnostics — offer consumer portals where you can order, visit a local patient service center for a blood draw, and receive results within 1–5 business days.

General process

1. Order online through QuestHealth.com or Labcorp OnDemand (ondemand.labcorp.com). No doctor's appointment needed. Must be age 18 or older to purchase (LabReqs is the only service that also offers titer ordering for those under 18).
2. Physician review: Behind the scenes, an independent contracted physician reviews and approves the test order — included in the purchase price. Quest charges a separate physician service fee of approximately $6.
3. Visit a patient service center with your requisition number and photo ID for a standard blood draw.
4. Results are available within approximately 1–5 business days, accessible through the patient's online account (Labcorp Patient portal or Quest MyQuest). Results can be downloaded and shared with schools, employers, or civil surgeons.

Available panels

• Labcorp OnDemand — Standard Immunity Test (5-in-1): Tests immunity to chickenpox (varicella), measles, mumps, rubella, and Hepatitis B in a single blood draw.
• Quest Health offers individual and combined titer tests including MMR Antibody Test Panel, Chickenpox (Varicella) Antibody Test, basic and expanded Vaccination Status Test Panels, and the QuantiFERON-TB Gold blood test.

A small number of states restrict direct-to-consumer lab ordering. Availability is shown on the platform's website based on your location. Always confirm your school or employer's specific requirements before ordering — some programs require particular lab brands or specific test codes.