Thyroid Stimulating Hormone (TSH) Lab Values

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Outline

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. 
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Transcript

Hey everyone, Abby here with nursing.com. This lesson we’ll talk about TSH, or thyroid stimulating hormone, it’s normal values, and when it would be increased or decreased. That’s right, we’ll be talking about the negative feedback loop. Let’s get started. Thyroid stimulating hormone or TSH is released from the anterior pituitary gland in response to low levels of thyroid hormone. TSH is the intermediary hormone that stimulates the thyroid gland to release the thyroid hormones. Do you recall the hormone negative feedback loop system? Let’s cover it briefly. TRH is produced by the hypothalamus. TRH is thyrotropin releasing hormone. It stimulates the anterior pituitary gland to produce TSH. The lab value for this lesson. TSH stimulates our thyroid gland to produce T3 and T4. The thyroid hormones once T3 and T4 are detected in the system through circulation in the hypothalamus, the release of TRH is inhibited. 

 

This inhibits the release from the anterior pituitary gland of TSH, because we’re good. We’ve got plenty of the T3 and T4. So we can really say that TSH and T3, T4 have an inverse relationship. We’ll look at this a little bit more closely when we talk about the lab value itself times when this lab is taken is to diagnose either hyper or hypothyroidism. It also indicates the functionality of our anterior pituitary, since it is what secretes the thyroid stimulating hormone. It’s also measured to look at and monitor thyroid replacement therapy. Normal values are between two and 10 milli units per liter. And it’s drawn into a plasma separator tube, a green top like this one when the increase of TSH is noted, that tells us the presence of hypothyroidism. It can also mean a thyroidectomy. If you don’t have a thyroid, can you produce T3 or T4? 

 

No. And if those are low, what did we just talk about? The TSH is gonna be high, right? So any thyroid dysfunction or abnormality inflammation, all of those types of issues with the thyroid, if it’s low, we’re going to see an increase in the TSH. Large doses of iodine will also increase TSH values as will a tumor that’s producing too much TSH. When lab values are decreased for TSH it means that there is usually hypersecretion of the thyroid hormones like T3, T4. It can also mean that the anterior pituitary isn’t functioning well, therefore it’s not secreting. The TSH linchpins for this lesson are that the thyroid stimulating hormone indicates glandular function of both the thyroid, as well as the anterior pituitary gland because of the negative feedback loop. It also helps us to monitor treatment for hyper and hypothyroidism. Normal values are between two and 10 millions per liter. 

 

And when it’s increased, that’s a lack of thyroid hormone. So just remember if the TSH is increased, the lower the thyroid hormone lab value will be T3 and T4. And the opposite is true as well. So when the TSH is low, it means that we’ve got plenty of thyroid hormone because through the feedback loop, we know that the TRH is not being produced and therefore it’s not producing from the anterior pituitary gland, the TSH, because we got plenty of the thyroid hormone. Always remember that negative feedback loop system. Now you all did great on this lesson. We love you guys know, go out and be your best self today, and is always happy nursing.

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