Thyroid Antibodies Test: TPO, Thyroglobulin, and TSI Explained

What Are Thyroid Antibody Tests?

Thyroid antibody tests detect immune proteins that mistakenly target the thyroid gland. In autoimmune thyroid disease, the immune system produces antibodies against thyroid structures, and finding them in blood helps explain why the thyroid is underactive or overactive. The three antibodies most often tested are thyroid peroxidase (TPO) antibodies, thyroglobulin antibodies (TgAb), and thyroid-stimulating immunoglobulin (TSI), sometimes measured as TSH-receptor antibodies (TRAb).

Each test is a simple blood draw, and fasting is usually not required. Antibody tests are almost always ordered alongside TSH, free T4, and often free T3, because antibodies alone cannot show whether hormone levels are currently high, low, or normal. The combination of hormone levels plus antibodies is what identifies the underlying cause.

Which Antibody Is Which

Understanding what each antibody targets makes the results far easier to read:

TPO antibodies are the most commonly ordered because they appear in the majority of Hashimoto cases and in many Graves cases as well. TSI is more specific: it mimics TSH and drives the thyroid to overproduce hormone, which is the hallmark of Graves disease.

Normal Ranges and Positive Results

Reference ranges vary by laboratory and assay, so your result must be read against your own report. In general, antibody results are reported as negative (normal) below the laboratory cutoff or positive (elevated) above it, sometimes with a numeric titer showing how high the level runs.

• Positive TPO antibodies with high TSH and low free T4 commonly point to Hashimoto thyroiditis, the leading cause of an underactive thyroid.
• Positive TPO or TgAb with normal hormone levels may signal early autoimmunity worth monitoring over time.
• Positive TSI with low TSH and high free T4 or T3 commonly points to Graves disease, the leading cause of an overactive thyroid.
• Negative antibodies do not fully rule out autoimmune disease, since some cases are antibody-negative early on.

Low-level positive results occur in a small share of healthy people too, so a positive antibody finding is interpreted with hormone levels, symptoms, and sometimes ultrasound before any conclusions are drawn.

When to Get Tested

Consider antibody testing if you have an abnormal TSH, a visibly enlarged thyroid (goiter), a family history of thyroid or other autoimmune disease, or symptoms such as persistent fatigue, feeling cold, unexplained weight change, tremor, palpitations, or eye irritation and bulging. Antibodies are also commonly checked during fertility evaluation and pregnancy planning, since untreated thyroid autoimmunity can affect pregnancy, and in newborns of mothers with Graves disease history.

After a diagnosis, clinicians may recheck antibodies occasionally to track the autoimmune process, though hormone levels remain the main guide for day-to-day management. This guide is educational information, not medical advice.

Reading Antibodies Together With Hormone Levels

Antibodies tell you about the immune process, while TSH and free T4 tell you what the gland is doing right now. A person can have positive antibodies with perfectly normal hormone levels, and that combination often means monitoring rather than immediate action. Reading the two together is what separates an active hormone problem from a background autoimmune tendency.

A single abnormal value rarely stands alone. Symptoms, the direction of the hormone change, and repeat testing over time all shape what the pattern means.

What Can Affect Antibody Results

Antibody assays vary between laboratories, so cutoffs and numeric titers are not directly comparable across different labs. High-dose biotin supplements can interfere with some thyroid immunoassays and produce misleading results, so list all supplements for the lab and pause biotin before testing if advised. Pregnancy and recent illness can shift immune markers, and antibody levels can fluctuate over time in the same person. A borderline result is often repeated on the same platform before conclusions are drawn.

How to Order Thyroid Antibody Tests

You can get antibody testing through a clinician visit or through direct-access lab testing. With the direct route, you order TPO, thyroglobulin antibody, or TSI tests online, receive a lab order by email, and visit a nearby CLIA-certified collection site for the blood draw. No physician visit or insurance approval is needed. Morning collection is common because TSH follows a daily rhythm, and you should list any thyroid products and biotin-containing supplements for the lab, since high-dose biotin can interfere with some assays.

Results typically arrive in a secure online account within one to three business days. Bring both the antibody results and the accompanying hormone levels to any clinical follow-up, since the two together tell the complete story.

How Much Do Thyroid Antibody Tests Cost?

Through direct-access sellers, a single antibody test such as TPO antibodies typically costs between about $40 and $90. A two-antibody bundle of TPO plus thyroglobulin antibodies commonly runs $70 to $150, and adding TSI or a full thyroid panel with TSH, free T4, and free T3 often brings the total to $120 to $250.

Full thyroid-plus-antibody bundles usually cost less than buying each marker separately, so compare package options if you need the complete picture. Check whether the quoted price includes the collection fee and how results are delivered before ordering.

How Often to Retest

Repeat antibody testing depends on the clinical question. After a new diagnosis, clinicians may recheck antibodies occasionally to track the autoimmune process, though hormone levels remain the main guide for day-to-day management. During pregnancy, antibody status may be checked at specific points because it can affect monitoring. Outside those situations, frequent retesting rarely changes care. Use the same laboratory when comparing results, and bring the accompanying hormone levels to every review so the pattern stays complete.