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Investigation of Thyroid Disease Two Hormones ‐ T3 & T4 T4‐Only thyroidal source Thyroid Physiology T3‐20% from thyroid secretion 80% from T4 in other tissues > 99% protein – bound hormones FT4‐0.05% FT3‐0.5% Reverse T3 Thyroid Regulation Stimulation by TSH Negative feed‐back. TSH under TRH control Thyroid Hormone Estimation (1)T3, T4, FT3, FT4 & TSH. Radio‐immunoassay ELISA Chemiluminiscence (2)Binding ratio (Resin uptake) (3)TBG level Why Free hormone levels? Metabolically active forms Not affected by binding protein disorders. TBG excess ‐ Estrogen therapy, pregnancy, hepatitis, congenital. Low TBG ‐ Androgen therapy, chronic liver disease. Thyroid Stimulating Hormone Single best test for thyroid disease. When T3 & T4 are high‐TSH is low. When t3 & T4 are low ‐ TSH is high Use of TSH level ‐ Diagnosis & follow ‐ up of thyroid dysfunction. TRH Stimulation Test. Best Assays To Order TSH FT4 T3 if T3 toxicosis is suspected. TFT Patterns T3 T4 TSH Diagnosis Low low high Primary hypothyroidism Low low low Pituitary hypothyroidism High high low Hyperthyroidism High high high TSH secreting tumour Resistance to Thyroid hormones Antithyroid Antibodies Inhibiting antibodies: TMA or TPO antibody Anti‐thyroglobulin antibody In Hashimotos Thyroiditis ‐ TMA + ve in 95% TGA + ve in 55% TPO + ve ‐ future hypothyroidism Stimulating Antibodies Thyroid Stimulating Immunoglobulins Positive in Graves disease Measured by c‐AMP production by Graves serum In thyroid cells Useful in predicting neo ‐ natal thyrotoxicosis Thyroglobulin Found in colloid Site of T3 & T4 synthesis. High TG – Hyperthyroidism Thyroiditis Smoking Low TG‐Athyreosis Use of TG estimation – Follow ‐ up of thyroid cancers Radioactive Iodine Uptake Thyroid gland concentrates Iodine Normal – 25 % after 24 hours Use ‐ in thyrotoxicosis only ‐ High in Graves disease,toxic MNG, toxic solitary nodule. Low in factitious thyrotoxicosis, sub ‐ acute & post ‐ partum thyroiditis Iodine induced thyrotoxicosis Thyroid Scan I 123 or Technitium ‐ 99m Use ‐ to assess function in thyroid nodules Hot ‐ hyperfunctioning Cold – non ‐ functioning 20 % malignant Ultrasonography 1. Diagnostic‐For thyroid nodules Benign‐anechoic,floating debris+‐ or hyperechoic with eggshell calcification Malignant ‐ Hypoechoic Irregular margins Microcalcification 2. Follow‐up Fine Needle Aspiration Cytology Safe OP procedure. 90 – 95 % accurate Useful in solitary nodule Dominant nodule in MNG Thyroiditis ? US guided Calcitonin From para ‐ follicular C cells ? physiological role High in Medullary carcinoma, MEN II Use‐in families with MTC, MEN II For early diagnosis & Follow ‐ up Genetic studies