MON-456 Abnormal Thyroid Function Tests-To Treat or Not to Treat

Abstract Disclosure: W. Akhter: None. R. Akhter: None. A.J. Zaidi: None. J.L. Gilden: Novartis Pharmaceuticals. IntroductionThyroid disorders are common, affecting more than 10% of people in the US. Apart from understanding normal physiology, it is important to be familiar with possible pitfalls and caveats in the use of thyroid function tests (TFT) tests, so that they can be interpreted accurately. When results are discordant, it is important to consider possible assay interferences and/or the effect of medications. In addition, thyroid function may appear abnormal in the absence of actual dysfunction in pregnancy and in critical illness. Therefore, it is important to consider the clinical context when interpreting TFT.Case PresentationWe present the case of a 41-year-old female who presented to the Endocrine clinic for evaluation and management of abnormal TFT. Patient endorsed symptoms of 25 lb. weight gain, severe fatigue, feeling foggy, joint pains, hair loss and constipation, which started after childbirth. Thyroid exam was normal. Thyroid ultrasound was normal. Both father and sister have Hashimoto’s thyroiditis. As a nurse, she self-diagnosed herself with postpartum thyroiditis with low TSH 0.058 uIU/mL (Normal = 0.550-4.780 uIU/mL), low Free T4 0.8 ng/dL (Normal= 0.89-1.76 ng/dL) and normal Free T3 3.65 pg/mL (Normal = 2.30-4.20 pg/mL). She convinced her primary care provider to prescribe levothyroxine 50 mcg daily but had little improvement in symptoms. Laboratory values 3 months later, when the patient presented to the endocrine clinic: TSH =0.137 uIU/mL, normal Free T4 =1.26 ng/dL and Free T3 2.98 pg/mL. with positive thyroid peroxidase antibodies, >2000. Repeat labs two months later showed normal TSH 0.880 uIU/mL, Free T4 1.17 ng/dL and Free T3 3.28 pg/mL Peroxidase antibodies >1500 while still taking the same dose of Levothyroxine 50 mcg daily, with symptomatic improvement. ConclusionNormal changes in thyroid physiology during pregnancy and the postpartum period make TFT interpretation very challenging. Owing to the structural similarity between Hcg and TSH, high Hcg levels during pregnancy stimulate TSH receptors, resulting in thyroid gland enlargement, increased thyroid hormone production and decreased TSH levels. After pregnancy when Hcg levels fall, free thyroid hormones decrease and TSH increases. Women who have a history of autoimmune thyroid disease or other forms of autoimmunity may develop postpartum thyroiditis, the incidence of which is approximately 5.4%. Postpartum thyroiditis follows a triphasic pattern and usually starts with transient hyperthyroidism followed by transient hypothyroidism and eventually a euthyroid state. Most cases of postpartum thyroiditis do not require treatment. However, some patients do not follow this classical pattern. Therefore, it is important to recognize that changes of TFT can occur in the postpartum state. In addition, not all symptoms of fatigue and weight gain can be attributed to hypothyroidism. Presentation: Monday, July 14, 2025