Thyroid Studies (DM)

Thyroglobuin

Stored thyroid hormone

Thyroxine / T4

Thyroid Prohoromone

Triiodothyronine / T3

Active thyroid hormone

Steps of Thyroid Hormone Pathway

Step 1: TRH released by hypothalamus

Step 2: TSH released by anterior pituitary

Step 3: T4 and T3 are released from thyroid into circulatory system and target tissues

Step 4a: T4/T3 in circulatory system causes decreased release of TRH

Step 4b: T4 is converted into T3 in peripheral tissues

What is the relationship between T3/4 and TRH

Inverse (Low levels of T3/4 cause increase of TRH)

Basic Thyroid Studies

Thyroid Stimulating Hormone (TSH)

Free T4

Occasionally free T3

Advanced Thyroid Studies

Thyroglobulin

Antithyroglobulin Antibody

Antithyroid Peroxidase Antibody (Anti-TPO

Indication for TSH Level

Diagnosing hypothyroidism and hyperthyroidism

Differentiating primary thyroid disease from secondary and tertiary causes

Monitoring effectiveness of medication for primary hypo or hyperthyroidism

What is often used for assessing thyroid function

TSH

When is TSH not used to assess thyroid function?

Pituitary / hypothalamus disease is known

Hospitalized

What medication increases TSH level

Lithium

What medications decreases TSH level

Dopamine Agonist

High Dose Steroids

What medicationis falsely elevates TSH

Biotin

How does pregnancy affect TSH

Decrease in the first trimester

What conditions cause elevated TSH

Primary hypothyroidism

TSH secreting tumor

Euthyroid Sick Syndrome

Normal TSH

0.4 - 4.2

What conditions can lower TSH

Secondary hypothyroidism

Tertiary hypothyroidism

Primary hyperthyroidism

Supression from thyroid medication

Biotin

Euthyroid Sick Syndrome

What binds to circulating thyroid hormone

Thyroxine-Binding Globulin (TB G)

How does pregnancy affect T3/4

Increases TBG

False increase total T4 but normal Free T4

What medication decreases T3/T4

Lithium

What medication falsly elevated T3/T4

Biotin

What conditions increase T3/T4

Hyperthryoidism

Acute Thyroiditis

Toxic Multinodular Goiter

Biotin

Normal Total T4

57-148

Normal Serun T4

0.7 - 2

Normal Total T3

1.3- 3.28

Normal Free T3

260-480

What conditions decrease T3/T4

Hypothyroid state

Pituitary insufficiency

Hypothalamic failure

Euthyroid sick syndrome

Primary Hypothyroidism

Failure of the thyroid to produce T3 and T4

Most common cause of Primary Hypothyroidism

Hashimoto’s Thyroditis

Antibodies to TPO and thyroglobulin is an indicator for

Hashimoto’s Thyroditis

Secondary Hypothyroidis

Failure of the pituitary gland to secrete TSH when appropriately stimulated by the hypothalamus

Tertiary Hypothyroidism

Failure of the pituitary gland to secrete TSH when appropriately stimulated by the hypothalamus

What is the work-up of hypothyroidism

1. TSH

2. If TSH is elevated or suspect = Serum Free T4

A high TSH with Low Free T4 indicates

Primary hypothyroidism

A high TSH with normal free T4 indicates

Subclinical Hypotyroidsm

A low to normal TSH with low Free T4 or T3 indicates

Central (Secondary/Tertiary) Hypothyroidism

Central Hypothyroidism

A condition of hypothyroidism where the failure is not in the thyroid gland

If TSH and Free T4 indicate Central Hypothyroidism, what test should be ordered next

Pitutary Function (FSH, LH , Prolactin, IGF-1, Serum 8am Cortisol)

Most Common Cause of Hyperthyroidism

Grave’s Disease

Grave’s Diease

Autoimmune disorder - causes stimulation of TSH receptor AB

Causes increased thyroid gland growth

Increases thyroid hormone production and release

Causes of Hyperthyroidism

Grave’s Disease

Toxic multi-nodular goiter

Toxic adenoma

Acute thyroiditis (ex: post-viral, postpartum)

Pituitary adenoma

What is the work-up for Hyperthyroidism?

1. TSH

2. If low, order Free T4 and T3

A low TSH with high T3/T4 indicates

Overy hyperthyroidism

A low TSH, high free T3, and normal free T4 indicates

T3 Thyrotoxicosis

A low TSH, high free T4, and normal T3 indicates

T4 Thyrotoxicosis

A low TSH with normal T3/T4 indicates

Subclinical hyperthyroidism

A normal to high TSH with high T3/T4 indicates

Pituitary Adenoma

Euthyroid Sick Syndrome

A condition that is Secondary to a nonthyroidal acute illness

Patho of Euthyroid Sick Syndrome

cytokines decrease activity of enzyme responsible for converting T4 to T3 in periphery

A normal TSH, normal T4, and low T3 indicates

Initial Euthyroid Sick Syndrome

A low TSH and low T3/T4 indicates

Severe Euthyroid Sick Syndrome

When should euthyroid sick syndrome be rechecked

4 weeks after recovery from illness

Use for Thyroglobulin

monitor patients with differentiated thyroid cancer for persistent or recurrent disease AFTER initial surgical therapy

Use of Antithyroglobulin Antibody

used when suspect an autoimmune thyroid disease (w/ Anti-TPO antibody)

ordered with thyroglobulin in patients with treated thyroid cancer

If Antithyroglobulin Antibodies are present, what changes in the treatment of thyroid cancer

Thyroglobulin cannot be used to track

Causes of Antithyroglobulin Antibody Elevation

Hashimoto’s thyroiditis

Grave's disease

Thyroid carcinoma

Other autoimmune conditions

10-20% of healthy individuals

Use of TPO Antibody

ordered with thyroglobulin antibody to increase sensitivity of test when assessing patients with subclinical disease to determine likelihood of becoming overt disease