Anti-TPO antibodies are present in: September 2007

Ans. C: Hashimotos thyroiditis Laboratory investigation of hypothyroidism: In the presence of suggestive symptoms and physical findings, a serum TSH test is needed for the diagnosis of primary hypothyroidism, and it serves to assess the functional status of the thyroid. - This is a sensitive test of thyroid function; levels are invariably raised in hypothyroidism due to Hashimoto's thyroiditis and in primary hypothyroidism of any cause. - The TSH level is also elevated in subclinical hypothyroidism and is usually the initial laboratory abnormality detected as the pituitary gland attempts to increase thyroid hormone production from the failing thyroid gland. The total T4 or free T4 usually remain within reference ranges in subclinical hypothyroidism. - The TSH level may also be elevated in the recovery phase of euthyroid sick syndrome. Medications that suppress TSH production include steroids, dopamine, dobutamine, and octreotide. A free T4 is usually needed to correctly interpret the TSH in some clinical settings. A low total T4 or free T4 level in the presence of an elevated TSH level fuher confirms the diagnosis of primary hypothyroidism. When a total T4 study, rather than a free T4 study, is performed, a T3 resin uptake helps to correct the total T4 and T3 values for protein binding, especially thyroid hormone-binding globulin (TBG) abnormalities, but the FT4 is typically the test of choice. T3 levels are most often maintained within reference ranges (even in the very late stages of hypothyroidism), and T3 measurement has little value in the diagnosis of hypothyroidism. The presence of thyroid autoantibodies, typically anti-TPO (anti thyroid peroxidase) and also anti-Tg (anti-thyroglobulin) antibodies, delineates the cause of hypothyroidism as Hashimoto's thyroiditis or its variant. However, 10-15% of patients with Hashimoto's thyroiditis may be antibody negative.