Thyroid . Patient guide
Thyroglobulin Antibodies (TgAb) Blood Test
Also known as: Anti-thyroglobulin, Anti-Tg
What is TgAb
Thyroglobulin antibodies are the second autoantibody used to confirm autoimmune thyroid disease alongside TPO antibodies. They are particularly useful when TPO antibodies are negative but autoimmune disease is still clinically suspected, and they have an additional role in monitoring after thyroid cancer treatment.
This biomarker entry is being clinically reviewed by our team. The factual content draws on UK guidance (NICE, NHS, Royal Colleges and the relevant speciality society where cited).
Reference range
Reported in IU/mL. Final reports always carry the issuing laboratory's range, which is what your clinician will interpret against.
| Group | Range | Note |
|---|---|---|
| Negative | under 115 | IU/mL; threshold varies between UK labs |
| Weakly positive | 115 to 500 | |
| Strongly positive | over 500 |
What it is
Thyroglobulin is the precursor protein the thyroid uses to make T4 and T3. In autoimmune thyroid disease the immune system can produce antibodies against this protein as well as against the TPO enzyme. Around 60 to 80 percent of patients with Hashimoto's thyroiditis have positive TgAb, and around 30 to 50 percent of patients with Graves' disease. A small proportion of healthy individuals (especially women over 50) carry low-titre TgAb without ever developing thyroid disease.
Why a clinician would order it
TgAb is requested when TPO antibodies are negative but autoimmune thyroid disease is still suspected (the two antibodies are complementary, not redundant), in differentiated thyroid cancer follow-up (where TgAb interferes with thyroglobulin tumour-marker measurement), and as part of a comprehensive thyroid antibody screen in patients with multiple autoimmune conditions, hair loss with normal thyroid function, or recurrent miscarriage where thyroid autoimmunity is a relevant risk factor.
If your level is outside the range
Symptoms of low TgAb
- No symptoms attributable to absent TgAb
What low can indicate. Autoimmune thyroid disease is unlikely if both TPO and TgAb are negative. A negative TgAb alone does not exclude autoimmunity since TPO antibodies are positive in some TgAb-negative cases.
Symptoms of high TgAb
- Symptoms relate to thyroid dysfunction if present: fatigue, hair shedding, weight change, cold or heat intolerance, mood changes. As with TPO antibodies, many patients with raised TgAb have normal thyroid function for years before clinical disease develops.
What high can indicate. Hashimoto's thyroiditis (the commonest cause, typically alongside positive TPO antibodies), Graves' disease, postpartum thyroiditis, differentiated thyroid cancer (where TgAb must be measured alongside thyroglobulin because it interferes with the cancer marker assay), or low-titre positivity in healthy individuals.
Testing tips
No fasting required. Antibody levels do not fluctuate significantly day-to-day so timing is flexible. Most useful interpreted alongside TPO antibodies and TSH; isolated TgAb positivity is less specific than positive TPO. In post-thyroidectomy cancer follow-up, TgAb must be measured every time thyroglobulin is measured because it can falsely lower the tumour marker result.
Where you can get this tested
Thyroglobulin Antibodies is included in the following WMG Health panels. Same-day appointments at our Harley Street clinic, with results clinician-reviewed.
Want a specific combination of markers we do not have a panel for? Build a custom panel and our clinicians will design one for you.
Looking to book a test?
Comprehensive private thyroid blood test
TSH, Free T4, Free T3 + TPO antibodies. NICE-aligned interpretation by GMC-registered doctors.
Symptoms often investigated with Thyroglobulin Antibodies
Thyroglobulin Antibodies is commonly tested when patients present with the following symptoms. If any of these resonate with you, the linked guides explain what to look for and which test pathway is appropriate.
Sources
UK guidance our clinicians use when interpreting this marker.
This page is general patient information, not personal medical advice. A GMC-registered clinician will review your results and tailor any interpretation to you. See our Editorial Policy for how we write and review content.
Common questions about TgAb
What is a normal TgAb range?
Negative: under 115 (IU/mL; threshold varies between UK labs). Weakly positive: 115 to 500. Strongly positive: over 500. Always interpret your own results against the laboratory range printed on your report, since assay-specific reference ranges vary.
What does a low TgAb result mean?
Autoimmune thyroid disease is unlikely if both TPO and TgAb are negative. A negative TgAb alone does not exclude autoimmunity since TPO antibodies are positive in some TgAb-negative cases.
What does a high TgAb result mean?
Hashimoto's thyroiditis (the commonest cause, typically alongside positive TPO antibodies), Graves' disease, postpartum thyroiditis, differentiated thyroid cancer (where TgAb must be measured alongside thyroglobulin because it interferes with the cancer marker assay), or low-titre positivity in healthy individuals.
Do I need to fast or prepare for the TgAb blood test?
No fasting required. Antibody levels do not fluctuate significantly day-to-day so timing is flexible. Most useful interpreted alongside TPO antibodies and TSH; isolated TgAb positivity is less specific than positive TPO. In post-thyroidectomy cancer follow-up, TgAb must be measured every time thyroglobulin is measured because it can falsely lower the tumour marker result.
Can I order a TgAb blood test privately in London?
Yes. WMG Health offers TgAb as part of bespoke panels and several pre-built panels at our 134 Harley Street clinic. Results are clinician-reviewed by a GMC-registered doctor within 4 hours for the most common assays. All panels are custom-built around your specific question; bookings via /contact/ or 020 3239 3378.