What Is a Titer Test?

A titer test (also called serology or antibody testing) is a blood test that measures the level of antibodies in your blood against a specific disease. A sufficient titer level indicates immunity — meaning your immune system has the antibodies needed to protect you from that disease, either from prior vaccination or natural infection.

When Are Titers Used for Immigration?

For the immigration medical exam, titers can be used to demonstrate immunity to certain vaccine-preventable diseases without requiring revaccination. This is particularly useful when:

• You have lost your vaccination records and cannot obtain them
• You received vaccines in another country and records are unavailable
• You had the natural disease (e.g., chickenpox) and want to confirm immunity
• You are unable to receive certain vaccines due to medical contraindications

Which Titers Does USCIS Accept?

USCIS accepts titer testing as evidence of immunity for the following vaccines:

• Measles (Rubeola) — IgG antibody titer
• Mumps — IgG antibody titer
• Rubella — IgG antibody titer
• Varicella (Chickenpox) — IgG antibody titer
• Hepatitis B — anti-HBs (hepatitis B surface antibody) titer

Interpreting Titer Results

Titer results are reported as either positive (immune/sufficient) or negative (non-immune/insufficient), along with a numerical value. The laboratory provides a reference range indicating the threshold for immunity.

A positive titer means you have sufficient antibodies to demonstrate immunity. No vaccination is required for that disease. A negative or equivocal titer means your antibody level is below the immunity threshold, and vaccination will be required.

What Happens If Titers Are Insufficient?

If a titer result is negative or equivocal (below the immunity threshold), you will need to receive the corresponding vaccine. For multi-dose vaccine series (such as hepatitis B), you may need to begin or complete the series. Your Civil Surgeon will advise on the appropriate vaccination schedule and whether your I-693 can be completed before the series is finished.

Titers vs. Vaccination Records

If you have documented vaccination records, titers are generally not required — your records serve as proof of vaccination. Titers are most useful when records are unavailable or incomplete. Note that for some vaccines (such as influenza and pneumococcal), titers are not accepted as a substitute for vaccination — the vaccine itself is required.

How Titer Results Are Documented on Form I-693

Titer results are documented in Part 5 of Form I-693 (Vaccination Record). Your Civil Surgeon records the titer test performed, the result, and whether immunity was demonstrated. If vaccination was required due to insufficient titers, the vaccination is also documented. The completed form is sealed and submitted to USCIS.