Thyroid antibodies: what anti-TPO and anti-Tg mean when your TSH is normal

What are thyroid antibodies?

The immune system protects the body from infection by producing antibodies that target foreign invaders. In some people, the immune system makes an error and starts attacking the body's own tissues, a process called autoimmunity. When this happens to the thyroid gland, the result is called autoimmune thyroid disease, and it is one of the most common autoimmune conditions worldwide.

Anti-TPO is an antibody that targets thyroid peroxidase, an enzyme the thyroid gland uses to produce its hormones T3 and T4. Anti-Tg targets thyroglobulin, the protein in which the gland stores its hormones before releasing them into the bloodstream. A raised level of either, or both, indicates that the immune system is mounting an attack on the thyroid gland. The gland may continue working normally for years despite this attack, which is why having raised antibodies does not automatically mean you are ill right now.

The most common form of this condition is Hashimoto thyroiditis, which is characterised by raised anti-TPO and a gradual, often very slow decline in thyroid function. Many people live for years or even decades with raised antibodies and a normal TSH. Others progress to subclinical and then overt hypothyroidism over time. Genetic studies published in PLoS Genetics in 2014 identified specific gene variants that influence the level of thyroid antibodies and the risk of progressing to clinical thyroid disease, confirming the hereditary component of this condition. There is no reliable way to predict for any individual how quickly things will progress, which is precisely why monitoring matters more than assuming an outcome.

Raised anti-TPO with a normal TSH: what does it mean in practice?

This is the scenario that causes the most confusion: a raised anti-TPO but a TSH in the normal range. The short answer is that the thyroid is still working adequately despite an ongoing immune attack. But this does not mean the situation can be dismissed entirely.

A review published in JAMA in 2019 on subclinical hypothyroidism examined evidence on patients with raised antibodies and found that the presence of anti-TPO significantly increases the long-term risk of progression to overt hypothyroidism compared to people with no antibodies. The risk is not certain for any individual, but it is real and measurable at a population level.

A study published in the Journal of Clinical Endocrinology and Metabolism in 2022 followed women who were anti-TPO positive with normal TSH before conception and found that a significant proportion developed thyroid insufficiency during or after pregnancy. This is the main reason why raised antibodies with a normal TSH warrants annual TSH follow-up rather than a single reassuring result and nothing further.

What is the difference between anti-TPO and anti-Tg?

Both are antibodies against the thyroid but they target different proteins. Anti-TPO is more sensitive and specific for Hashimoto thyroiditis and is typically the first test ordered. Anti-Tg may be raised in some cases where anti-TPO is normal and is also clinically important in monitoring patients after total thyroid removal for cancer, where thyroglobulin serves as a tumour marker.

A raised anti-Tg in isolation, without raised anti-TPO, is less specific for Hashimoto and can occasionally be found at low levels in otherwise healthy people. The two results are interpreted together and alongside the clinical picture, not in isolation. One number never tells the whole story.

Reference ranges for these antibodies differ between laboratories depending on the method and instrument used, which is one reason why results from different labs should be interpreted with caution when comparing them over time. Always compare your result to the reference range printed on your own laboratory report.

Symptoms of Hashimoto: when do they appear and how do you recognise them?

In many cases there are no obvious symptoms in the early stages and the antibodies are found by chance on a routine panel. When the gland begins to slow down, the symptoms that appear are the same as those of hypothyroidism generally: unexplained fatigue, weight gain despite no change in diet, feeling unusually cold, dry skin and hair, mental fogginess, constipation and irregular periods in women.

The difficulty is that these symptoms are non-specific and shared by many other conditions. It is not possible to diagnose Hashimoto or hypothyroidism from symptoms alone. Some people attribute their fatigue and weight gain entirely to Hashimoto when TSH is normal, and in that situation other causes also deserve investigation.

If you have raised antibodies and symptoms that bother you, the first step is measuring TSH. If TSH is elevated, treatment may be appropriate. If it is normal, the doctor will look for other explanations for the symptoms and establish a schedule for annual TSH monitoring.

Women and thyroid antibodies: what is the link with pregnancy?

Women are around seven times more likely to develop Hashimoto thyroiditis than men, and the condition is most common during the reproductive years. The presence of anti-TPO in a woman who is pregnant or planning to conceive deserves special attention because it is associated with an increased risk of miscarriage in the first trimester and with postpartum thyroiditis in the months after delivery.

A 2022 study in the Journal of Clinical Endocrinology and Metabolism found that women who were anti-TPO positive with a normal TSH before conception had a notably higher rate of developing thyroid insufficiency during pregnancy or in the postpartum period. This means that even a normal pre-pregnancy TSH does not fully reassure in the presence of raised antibodies. TSH should be checked at the first antenatal visit and monitored through the pregnancy.

If you are planning a pregnancy and have raised anti-TPO, raise this with your doctor before conception. It does not mean pregnancy is unsafe or that problems are inevitable, but it does mean that close TSH monitoring throughout the pregnancy is necessary rather than optional.

Is there any treatment that reduces the antibodies themselves?

No reliably proven medical treatment eliminates anti-TPO or reduces it permanently. A systematic review published in the journal Nutrients in 2023 examined the evidence for nutritional interventions in Hashimoto thyroiditis and found that dietary modifications such as reducing gluten and certain supplements including selenium showed modest antibody reductions in some studies, but the evidence is not strong enough to recommend these universally for all patients.

The main goal of management is monitoring TSH and treating it with levothyroxine when it rises above normal. Levothyroxine does not treat Hashimoto itself and does not lower the antibodies, but it compensates for the hormonal deficit, improves symptoms and protects the body from the consequences of hypothyroidism.

Marketing claims about supplements and herbal products that promise to correct thyroid autoimmunity are widely circulated in the region. Be cautious about any product claiming to fix Hashimoto. Some preparations contain iodine in amounts that can actually accelerate thyroid decline in people with autoimmune thyroid disease. Discuss any supplement with your doctor before starting.

Follow-up: how often and which tests?

If anti-TPO is raised with a normal TSH, most guidelines recommend measuring TSH once a year. There is no need to retest the antibodies themselves frequently because a change in their level does not usually change the treatment decision. What matters is tracking TSH.

If TSH begins rising above the normal range, this signals that the gland is gradually losing capacity. Free T4 is added at this point to assess whether the gland can still compensate for the demand. Some doctors start treatment when TSH exceeds 10, others when it is between 4 and 10 alongside clear symptoms. The decision is individualised and takes into account age, symptoms, cardiovascular risk and plans for pregnancy.

Some laboratories in the region do not perform these assays to standardised protocols and results may vary. If your anti-TPO is raised but TSH is consistently normal and you have no symptoms, it is worth repeating the antibody test at a well-equipped accredited laboratory before drawing firm conclusions.

Hashimoto thyroiditis in the regional context

In several countries in the Levant and wider Arab region, Hashimoto is sometimes diagnosed based on thyroid enlargement or symptoms alone without adequate laboratory testing. A correct diagnosis requires at minimum a TSH and anti-TPO measurement, with free T4 added if TSH is abnormal. A clinical impression alone, while sometimes accurate, lacks the precision needed to guide management decisions. The same applies to ultrasound findings of thyroid heterogeneity, which may support but cannot confirm the diagnosis without the blood tests.

Many patients in the region ask about the gluten and Hashimoto connection. Evidence does show an association between coeliac disease and Hashimoto thyroiditis, and some patients report symptom improvement after eliminating gluten. However, recommending a gluten-free diet to every Hashimoto patient without a confirmed coeliac diagnosis is not supported by sufficient evidence, and a gluten-free diet has nutritional implications and costs of its own. If you want to explore this, test for coeliac disease first before committing to the diet.

Hashimoto thyroiditis does not mean the thyroid will inevitably fail or that lifelong medication is certain. Many people live for decades with raised antibodies and a stable TSH. What varies between individuals is the speed of progression, and this is exactly what regular monitoring captures. The goal is not to fear the diagnosis but to understand it, track it intelligently, and intervene only when the evidence and your symptoms call for it. A person whose TSH stays normal for years is not untreated for a disease: they are under appropriate surveillance for a condition that has not yet required treatment.

Sources

• Medici M, Porcu E, Pistis G et al: Identification of novel genetic loci associated with thyroid peroxidase antibodies and clinical thyroid disease, PLoS genetics, 2014
• Biondi B, Cappola AR, Cooper DS et al: Subclinical Hypothyroidism: A Review, JAMA, 2019
• Collet TH, Bauer DC, Cappola AR et al: Thyroid antibody status, subclinical hypothyroidism, and the risk of coronary heart disease, The Journal of clinical endocrinology and metabolism, 2014
• Gill S, Cheed V, Morton VAH et al: Evaluating the Progression to Hypothyroidism in Preconception Euthyroid Thyroid Peroxidase Antibody-Positive Women, The Journal of clinical endocrinology and metabolism, 2022
• Gaitonde DY, Rowley KD, Sweeney LB et al: Hypothyroidism: an update, American family physician, 2012
• Osowiecka K, Myszkowska-Ryciak J: The Influence of Nutritional Intervention in the Treatment of Hashimoto Thyroiditis, a Systematic Review, Nutrients, 2023