Thyroid Lab Work (Nursing)

00:01 Let's take a look at specific lab work that will indicate how your thyroid gland is functioning.

00:08 Now timing matters for this for thyroid lab tests and you understanding why this matters will help you get more accurate and consistent results for your clients.

00:17 TSH (thyroid stimulating hormone) has the most significant daily variation. It follows a circadian rhythm, so it's highest in the late evening and early morning hours and it's lowest in the afternoon.

00:31 Now to understand why, imagine your body's hormone system like an orchestra. Different instruments, the hormones play their parts at different times to create a full symphony of your daily biological rhythms.

00:44 So the most accurate and consistent time to test TSH is early in the morning.

00:49 Ideally, you want it drawn between 8 a.m.

00:51 and 10 a.m.. Remember this timing is important because of three things. It helps ensure results are comparable between different tests over time.

01:00 Most reference ranges for TSH are based on morning draws, and third, the morning level tends to be more stable and representative of the baseline thyroid function.

01:11 Now, T3 and T4 show less dramatic daily variations in TSH, but they're still best measured in the morning for consistency.

01:19 However, there's one other important timing consideration with T3 and T4 testing, it's about the client's medication.

01:27 If the client takes thyroid medication like levothyroxine, the timing of the blood draw is relative to the last dose because this can significantly affect the results. That's because the thyroid medication can cause a temporary spike in thyroid hormone levels.

01:42 So think of it like taking a temperature reading right after drinking hot coffee, you wouldn't get an accurate reading of your true body temperature.

01:50 The same is true with medication and your lab work.

01:54 So for the most accurate results when you're on thyroid medication, you want to make sure that the blood draw is scheduled before taking the morning dose of the thyroid medication.

02:04 So if a client can't get a draw early in the morning, it's better to postpone the medication until after the blood draw rather than take it at a different time of the day.

02:14 Now that we have established that timing is really important for thyroid lab work. Let's take a look at the typical normal lab values for thyroid function tests.

02:24 Remember, these ranges can vary between different laboratories in the same method.

02:28 So these are just relative reference examples.

02:32 So always refer to the specific reference ranges provided by the testing laboratory. Let's start with TSH or thyroid stimulating hormone. We have the normal range for you on the screen.

02:45 Remember this varies by slightly by lab.

02:48 Now this is the most accurate test for initial thyroid screening.

02:52 It's inversely related to thyroid hormone levels.

02:55 So expect that a TSH level would be drawn.

02:58 TSH is often considered the most important screening test, but I want to point out that additional testing will be necessary.

03:06 You're going to also look at T4 levels, so keep this in mind.

03:09 I just wanted to give you some type of reference that what could a high TSH and a low TSH mean? Well, theoretically high TSH would likely suggest hypothyroidism.

03:22 That's because the thyroid hormone is not.

03:25 The thyroid is not making enough hormone.

03:28 So when TSH is high, this could generally suggest hypothyroidism, because that hypothalamus and anterior pituitary are putting out the hormones to stimulate that thyroid to make more hormones, and it's just not able to do that.

03:44 Keep in mind you're going to have to do additional testing.

03:47 As another general rule, low TSH suggests hypothyroidism.

03:52 Remember, it just suggests that you'll need more testing.

03:55 That would mean that the thyroid is making so much thyroid hormone.

03:59 The hypothalamus is like, whoa, let's back off on the on the hormones that will stimulate the thyroid to make more thyroid hormone.

04:08 That's why there would be less thyroid stimulating hormone available on their lab work. So we can also use TSH to monitor thyroid replacement therapy. So clients who are on replacement therapy will have routine TSH levels drawn because remember, it's the most sensitive early indicator of the thyroid dysfunction.

04:28 Now there's a lab work called free T4 or thyroxine.

04:32 We've got the normal range for you.

04:34 An example of it on the screen.

04:36 Now direct measurement of available T4 is what this test will do.

04:40 And it's not affected by protein binding.

04:42 So this is really helpful to know what is going on with the thyroid because it measures active unbound hormone that's available to the tissues.

04:51 Remember once it gets into the peripheral tissues it will convert it to T3 which is much more active. So a free T4 is ordered when TSH is abnormal just to help confirm the diagnosis.

05:03 Remember it's more accurate than total T4 because it's not affected by protein levels. That's why a free T4 is ordered.

05:10 So you can use this T4, the free T4 in diagnosing central hypothyroidism. That's when the TSH may be inappropriately normal.

05:19 So you can also use free T4 to monitor thyroid hormone replacement.

05:23 Is it helping us? Is it at an appropriate level? And you can also use a free T4 to assess how severe the thyroid dysfunction is. Now another lab work is a free T3.

05:35 We've got the normal range for you there on the screen.

05:37 Now remember T3 is the most active form of the thyroid hormone.

05:42 And it can actually be normal in early thyroid disease.

05:46 So remember trends and clinical signs and symptoms are always important when you're interpreting lab work.

05:51 So this free T3 measures the most biologically active thyroid hormone. So there's some important things to remember in specific situations. T3 thyrotoxicosis might occur where T4 might be normal. You might use it in monitoring hyperthyroid patients who are on treatment plans.

06:11 You might also use a free T3 to assess the conversion of T4 to T3 in clients who are sick.

06:18 Now, this is less commonly ordered than TSH and free T4, but we wanted to make sure that we covered it in this series.

06:26 Now total T4. You see the normal range there on the screen, and this one measures both bound and free T4.

06:33 And this one can be affected by protein levels.

06:36 Total T3. You see the normal range.

06:39 It measures again both bound and free T3.

06:43 So this is commonly less commonly used than a free T3.

06:47 So total T4 and total T3 are less commonly used now because they can be kind of misleading because they're both affected by protein levels. But it might be useful in very specific situations.

07:00 It might be useful in assessing binding protein abnormalities might be useful in pregnancy when binding proteins change, or if there's some type of suspected medication interference.

07:11 As we wrap up this discussion, we've created a study guide for you that has clinical pattern recognition based on multiple diagnoses you'll see what you should expect with the TSH and the free T4 levels.

07:24 So thanks for joining us for this video and good luck in your practice.