WHO SHOULD BE TESTED FOR THYROID DYSFUNCTION? Groups with an increased likelihood of thyroid dysfunction Previous thyroid disease or surgery Goitre Associated autoimmune disease(s) Diabetes mellitus Previous postpartum thyroid dysfunction Down's syndrome Irradiation of head and neck Radical laryngeal/pharyngeal surgery Recent Cushing's syndrome Drug therapy Amiodarone Lithium Biological agents Interferon a Interferon b Interleukin 2 Therapeutic use of antibodies Pituitary surgery or irradiation Severe head injury Very low birth weight premature infants

THYROID TESTS BIOCHEMICAL/HORMONAL TESTS DYNAMIC TESTS RADIONUCLEID TESTS IMMUNOLOGIC TESTS IMAGING METHABOLIC TESTS,PERIFERAL INDICES FNA

BIOCHEMICAL TESTS TSH T4,T3 T3RU FREE T4 INDEX (FTI) FREE T4,FREE T3 Tg OTHERS rT3,iodothyroins,Triac,Tetrac,compound W,Urine Iodine

PHYSIOLOGIC CONTROL OF THYROID HORMONE PRODUCTION

TSH  TSH Almost always =  Thyroid hormones Rarely central hyperthyroidism Thyroid hormone resistance  TSH Central hypothyroidism Thyrotoxicosis (clinical or subclinical) SES

The relationship between serum TSH and free T4 concentration is shown for normal subjects (N) and in the typical abnormalities of thyroid function: A, primary hypothyroidism ; B, central or pituitary-dependent hypothyroidism; C, thyrotoxicosis due to autonomy or abnormal stimulation of the gland; D, TSH-dependent thyrotoxicosis or thyroid hormone resistance. Note that linear changes in the concentration of T4 correspond to logarithmic changes in serum TSH.

T3RU It is an index of TBG If TBG  T3RU  If TBG  T3RU  T3RU * TOTAL T4 = FREE T4 INDEX

TBG Resin T4 Euthyroid

TBG Resin Hyperthyroid T4  T3RU  TSH 

Tg Indications : Suspicious thyrotoxicosis factitia Follow up of thyroid malignancy

RADIONUCLEID TESTS RAIU THYROID SCAN Tc99 I 123 I 131

Factors That Increase Uptake Increased hormone synthesis Hyperthyroidism Response to glandular hormone depletion Recovery from thyroid suppression Recovery from subacute thyroiditis Antithyroid agents Excessive hormone losses Nephrotic syndrome Chronic diarrheal states Soybean ingestion Normal hormone synthesis Iodine deficiency Dietary insufficiency Excessive loss (dehalogenase defect, pregnancy) Hormone biosynthetic defects

Factors That Decrease Uptake Decreased hormone synthesis Primary hypofunction Primary hypothyroidism Antithyroid agents Hormone biosynthetic defects Hashimoto's disease Subacute thyroiditis Secondary hypofunction Exogenous thyroid hormones Not reflecting decreased hormone synthesis Increased availability of iodine Diet or drugs Cardiac or renal insufficiency Increased hormone release

This is what a thyroid scan looks like with graves disease

MNG

Large cold nodule

IMMUNOLOGIC TESTS Anti TPO Anti Tg Anti TSHR

ULTRASOUND

CT Scan

Total T4 Total T3 T3Ru Hyperthyroidism  TBG   Hypothyroidism  TBG  

 Primary Hypothyroidism  Central Hypothyroidism TSH TSH  T4 T4  T3 T3 

TSH NL TSH NL T4 T4  T3 T3  * TBG effect

TSH TSH  T4 T4  T3 T3  Thyrotoxicosis Thyrotoxicosis Hyperthyroidism Hyperthyroidism RAIU

TSH TSHNL T4 T4  T3 T3  * Central Hypothyroidism * TBG Binding disorder * TBG 

TSH TSH  T4 NL T3 NL * Sub Clinical Hyperthyroidism (SH) * Drugs

TSH TSH  T4 NL T3 NL * Sub Clinical Hypothyroidism (SCH) * Non adherence to levothyroxine

FNA Fine-needle aspiration (FNA) biopsy of the thyroid gland is now an established, accurate diagnostic test that is routinely used as the first step in the evaluation of nodular thyroid disease.