From the Guidelines
The patient's lab results indicate the presence of autoimmune thyroid disease, as evidenced by elevated thyroid peroxidase antibodies, and further evaluation is necessary to assess thyroid function and potential IgG4-related disease, as recommended by recent guidelines 1. The lab results show several abnormal findings, including elevated Immunoglobulin G subclass 4 at 163.8 mg/dL, which is outside the reference range of 4.0-86.0 mg/dL, and thyroid peroxidase antibodies at 25 IU/mL, exceeding the reference range of <9 IU/mL.
- The elevated thyroid peroxidase antibodies suggest autoimmune thyroid disease, which is the most common autoimmune disorder associated with diabetes, occurring in 17–30% of individuals with type 1 diabetes 1.
- Free T3 is within the normal range at 3.6 pg/mL, indicating that thyroid function is currently maintained despite the autoimmune process.
- Thyroglobulin antibodies are normal at <1 IU/mL. Key considerations include:
- Assessing for additional autoimmune conditions soon after the diagnosis of type 1 diabetes and if symptoms develop, as recommended by the 2023 standards of care in diabetes 1.
- Recognizing that thyroid autoantibodies, particularly anti-thyroid peroxidase antibodies, are predictive of thyroid dysfunction, most commonly hypothyroidism 1.
- Understanding that thyroid function tests may be misleading if performed at the time of diagnosis due to the effects of previous hyperglycemia, ketosis, or ketoacidosis, and should be repeated after a period of metabolic stability and achievement of glycemic targets 1. Therefore, further evaluation is recommended, including complete thyroid function tests (TSH, T4), clinical assessment for symptoms of hypothyroidism, and potentially additional testing to evaluate for IgG4-related disease if clinically indicated by symptoms such as enlarged organs, lymphadenopathy, or unexplained fibrosis, prioritizing the patient's morbidity, mortality, and quality of life 1.
From the Research
Thyroid Peroxidase Antibodies and Thyroid Function
- Thyroid peroxidase antibodies (TPO-Abs) are associated with autoimmune thyroid disease, particularly Hashimoto's thyroiditis 2, 3, 4
- The presence of TPO-Abs can lead to thyroid dysfunction, including hypothyroidism and thyrotoxicosis 2
- TPO-Abs are also prevalent in healthy individuals, and their presence has been linked to an increased risk of mortality, particularly in men 5
Laboratory Testing for Thyroid Disorders
- Laboratory tests, including TSH, free thyroxine, free triiodothyronine, thyroglobulin, and TPO-Abs, are essential for diagnosing and managing thyroid disorders 3
- The interpretation of these tests requires consideration of the clinical context, including the presence of autoimmune disorders and the use of certain medications 3
Hashimoto's Thyroiditis and Cognitive Function
- Hashimoto's thyroiditis has been linked to cognitive impairment and decreased quality of life, even in patients on long-term levothyroxine replacement therapy 6
- The presence of TPO-Abs has been correlated with decreased cognitive function and quality of life in patients with Hashimoto's thyroiditis 6