What does a Tpo (thyroid peroxidase) value of 40 indicate?

Interpretation of TPO Value of 40

A thyroid peroxidase (TPO) antibody value of 40 is considered within normal range and does not indicate thyroid autoimmunity or increased risk for thyroid dysfunction. 1

Understanding TPO Antibodies

• TPO is a key enzyme in thyroid hormone production and a major autoantigen in autoimmune thyroid diseases 2
• TPO antibodies are markers of autoimmune thyroid disease, with elevated levels indicating potential autoimmune thyroiditis 1
• Normal TPO antibody values typically range up to 100-200 IU/ml, depending on the specific laboratory assay used 3
• A value of 40 falls within the normal range observed in healthy individuals without thyroid disease 4, 2

Clinical Significance of TPO Value of 40

• TPO values below 100 IU/ml are not associated with significantly different TSH levels compared to individuals with negative antibodies 5
• Only TPO antibody levels >500 IU/ml indicate a moderately increased risk for developing hypothyroidism 5
• In control groups and patients with non-thyroidal illness, mean TPO levels are typically around 26-39 units/ml 3
• A TPO value of 40 does not warrant additional thyroid testing based solely on this result 1

When to Consider Further Evaluation

• Further thyroid evaluation would be indicated if:
  • Clinical symptoms of thyroid dysfunction are present 1
  • TSH levels are abnormal 1
  • The patient has other autoimmune conditions that increase risk of thyroid disease 1
  • There is a family history of autoimmune thyroid disease 2

Monitoring Recommendations

• With a TPO value of 40, routine monitoring of thyroid function is not specifically indicated unless other risk factors are present 1
• If the patient has type 1 diabetes or other autoimmune conditions, annual thyroid function testing is recommended regardless of TPO status 1
• Pregnant women or those planning pregnancy with any detectable TPO antibodies may benefit from closer monitoring, even with values in the normal range 2

Important Considerations

• Very low titers of TPO antibodies can be found in virtually all subjects with modern sensitive assays, but values below the assay-dependent cut-off (typically 100-200 IU/ml) are not clinically significant 2
• TPO antibody status should always be interpreted in conjunction with thyroid function tests (TSH, free T4) for a complete clinical picture 1
• The presence of TPO antibodies, even at low levels, may have greater clinical significance in certain high-risk populations such as pregnant women or those with other autoimmune disorders 1, 2