Are Thyroid Peroxidase (TPO) antibodies elevated or decreased in Graves’ disease?

TPO Antibodies in Graves' Disease

TPO antibodies are typically elevated in Graves' disease, found in approximately 57-80% of patients at diagnosis. 1, 2

Prevalence and Clinical Significance

TPO antibodies are commonly present in Graves' disease, though less frequently and at lower levels than in Hashimoto's thyroiditis:

• 74% of Graves' disease patients test positive for anti-TPO antibodies, with concentrations ranging from 11-74,000 U/mL 1
• 80% of untreated Graves' patients demonstrate positive TPO antibodies in clinical studies 2
• 72% of Graves' disease patients show elevated anti-TPO antibody levels when measured by ELISA 3

This contrasts sharply with Hashimoto's thyroiditis, where 99.3% of patients have positive TPO antibodies 1, indicating that while TPO antibodies are common in Graves' disease, they are nearly universal in Hashimoto's.

Temporal Pattern of TPO Antibodies

TPO antibodies in Graves' disease show a gradual increase over time before clinical diagnosis, distinguishing it from Hashimoto's thyroiditis:

• TPO antibodies increase from 31% prevalence 5-7 years before diagnosis to 57% at the time of diagnosis 4
• This progressive pattern differs from Hashimoto's thyroiditis, where TPO antibodies remain stationary at approximately 66% at all time points before and after diagnosis 4

Effect of Treatment on TPO Antibody Levels

Anti-thyroid drug treatment significantly decreases TPO antibody levels in Graves' disease patients:

• TPO antibody levels significantly decrease after methimazole treatment 1
• However, iodine-131 treatment does not significantly affect anti-TPO antibody levels, though it does reduce TRAb levels 3

Clinical Pitfalls and Important Distinctions

The presence of TPO antibodies alone cannot distinguish between Graves' disease and Hashimoto's thyroiditis, as both conditions demonstrate these antibodies:

• TSH receptor antibodies (TRAb) are the distinguishing feature, present in 55-75% of Graves' disease patients at diagnosis but absent in Hashimoto's thyroiditis 4, 3
• In Graves' disease, TRAb shows an increasing prevalence from 2% to 55% in the years leading to diagnosis 4
• Physical examination findings of ophthalmopathy or thyroid bruit are diagnostic of Graves' disease and should prompt early endocrine referral 5

Associated Autoimmune Conditions

Graves' disease patients with elevated TPO antibodies have increased risk of other autoimmune conditions and should be screened accordingly:

• Screening for type 1 diabetes, celiac disease, and adrenal insufficiency is recommended when TPO antibodies are present 6
• Thyroid disorders are among the most common concurrent autoimmune diseases, accounting for 10.5% of cases in patients with other autoimmune conditions 5