Types

• Thyroxine (T4) is a hormone synthesized and secreted by the thyroid gland. In circulation 99.95 % of T4 is reversibly bound to transport protein, primarily Thyroxine binding Globulin (TBG) and to a lesser extent albumin and thyroxin binding pre albumin (TBPA). The remaining T4 is not bound to transport proteins but it is free in the circula...

Description

• 0.7 -1.8 ng/dl

When to get Tested

• When there is s/s of Hyperthyroidism (Increased heart rate, Anxiety, weight loss, difficulty sleeping, tremors in the hands, weakness, and menstrual irregularity)

Elevated Level

Graves disease

• Toxic multinodular goiter
• Toxic adenoma

Transient hyperthyroidism

• Subacute thyroiditis
• Hashimoto’s thyroiditis

Rarely

• Hyperthyroid secondary to pituitary disease
• Thyroid cancer

Decreased Level

Primary hypothyroidism

• Hashimoto’s thyroiditis
• Idiopathic myxedema
• Previous treatment of hyperthyroidism
• Sub-acute thyroiditis
• Prior neck radiotherapy
• Iodine deficiency or excess
• Congenital
• Medications- Lithium, Sulfonamides , Phenylbutazone , Amiodarone ,Thiourea

Secondary hypothyroidism

• Pituitary dysfunction

Tertiary hypothyroidism

• Hypothalamic disease- Very rare
• Tissue resistance to thyroid hormone