Thyroid Stimulating Hormone (TSH) Lab Values

Objective:

Determine the significance and clinical use of Thyroid Stimulating Hormone in clinical practice

Lab Test Name:

Thyroid Stimulating Hormone

Description:

Thyroid Stimulating Hormone (TSH) is released from the anterior pituitary in response to low levels of thyroid hormone.

TSH stimulates the thyroid gland to release thyroid hormones

• Triiodothyronine (T3)
• Thyroxine (T4)
• T3 and T4 have an inverse relationship with TSH

Indications:

Aids to diagnose:

• Hyperthyroidism
• Hypothyroidism
• Anterior pituitary function

Monitor:

• Thyroid replacement therapy

Normal Therapeutic Values:

Normal –

2-10 mU/L

Collection:

• Plasma separator tube

What would cause increased levels?

TSH levels increase in the following conditions:

• Hypothyroidism
• Thyroidectomy
• Thyroid dysfunction
• Thyroiditis
• Thyroid Agenesis
• Large doses of iodine
• Pituitary TSH-secreting tumor

What would cause decreased levels?

Recall the inverse relationship between TSH and T3/T4 labs, and how the negative feedback loop works with these hormones.

TSH levels decrease in the following conditions:

• Anterior pituitary hypofunction- If the pituitary isn't secreting TSH, the level will be low.
• Hyperthyroidism- If there is a large amount of thyroid hormone circulating, the feedback system relays the info upstream and less TSH is released.