00:00The TSH blood test is a common blood test clinicians use to monitor the function of your thyroid gland.
00:08So when the TSH is high, what does that mean?
00:13And when it is low, is that good or bad?
00:17TSH stands for thyroid stimulating hormone, and that is exactly what it does.
00:23It stimulates the thyroid gland to produce thyroid hormones.
00:29You would therefore expect that when the TSH is high, there should be more thyroid hormone in the circulation.
00:37But it's not that simple.
00:39The pituitary gland, a small gland beneath the brain, produces TSH.
00:46The job of TSH is to tell your thyroid gland to produce thyroid hormones, primarily T4 and T3.
00:58You can think of the pituitary gland as a thermostat and the thyroid gland as a furnace.
01:05When the body does not have enough thyroid hormone, the thermostat turns up the signal.
01:13The pituitary releases more TSH, telling the thyroid gland to work harder.
01:19When there's too much thyroid hormone, the pituitary turns down the signal, and the TSH falls.
01:28This feedback system explains the most common thyroid test patterns.
01:33Let's begin by taking a look at an underactive thyroid result.
01:40If the thyroid gland becomes damaged and cannot produce enough thyroid hormone, the free T4 falls.
01:50In response, the pituitary gland turns up the thermostat.
01:55It produces more TSH.
01:58So in an underperforming thyroid, we see a high TSH and a low free T4.
02:07This is called primary hypothyroidism because the sickness, the problem, begins in the thyroid gland itself.
02:18Now consider an overactive thyroid gland.
02:22If the thyroid gland produces too much thyroid hormone, the free T3 or T4 rises.
02:31The pituitary realizes that the body already has enough thyroid hormone and turns down the thermostat.
02:37It suppresses the TSH.
02:39So in an overactive thyroid gland, we see a low TSH and a high free T4 or T3.
02:50And this is called primary hyperthyroidism.
02:54But this is where interpreting the thyroid becomes more interesting.
02:59Sometimes the TSH is elevated, but the free T4 remains normal.
03:04And this is called subclinical hypothyroidism.
03:08The word subclinical can be confusing.
03:12It doesn't mean that the result is unimportant or that the patient cannot have symptoms.
03:19It means that the TSH is abnormal while the free T4 remains within the normal range.
03:27This can happen because the pituitary is highly sensitive to even slight changes in the thyroid hormone levels.
03:36It may increase the TSH before the free T4 falls below normal.
03:43Doctors will often repeat a slightly elevated TSH because it may return to normal,
03:49particularly when a temporary illness has taken place.
03:54Treatment depends on several factors, including how high the TSH is, whether it remains elevated,
04:04the person's age and symptoms, TPO antibody results, heart-related risk factors,
04:12and whether the patient is pregnant or planning pregnancy.
04:16A persistent TSH above approximately 10 milli-international units per liter is taken more seriously and is commonly treated.
04:28However, for results below 10, your doctor will look at the complete picture and decide whether to treat you or
04:37not.
04:38There is one more important pattern that many patients and occasionally even clinicians can miss.
04:47What happens when the thyroid gland is healthy, but the pituitary gland is not sending an adequate signal?
04:56This is called central hypothyroidism.
05:01In central hypothyroidism, the free T4 is low, but the TSH may be low, normal, or occasionally slightly elevated.
05:13The thermostat is not responding to the weak heat in the furnace.
05:20The TSH is not responding appropriately to the low thyroid hormone level.
05:27As we can see, a normal TSH does not always rule out hypothyroidism,
05:32particularly when pituitary disease is suspected.
05:37In that situation, the free T4 becomes especially important.
05:42The opposite pattern, that's a high thyroid hormone with a TSH that is not suppressed, can also occur.
05:52Because of the various causes of this scenario, your doctor might recommend that you see a thyroid specialist.
06:00The simplest way to remember all this is,
06:04TSH tells you how loudly the pituitary gland is calling for thyroid hormone.
06:10Free T4 tells you how much thyroid hormone is actually being produced by the thyroid gland.
06:17That is why it is best not to read your TSH by itself.
06:22To understand what your thyroid results are truly saying,
06:27look at the TSH and free T4 together,
06:30and pay attention to the whole clinical picture.
06:35I hope you found this useful.
06:37If you did, like, share this video with your friends and family.
06:42Leave your comments in the box below.
06:44You can support this channel by subscribing.
06:47Until the next video, stay healthy and stay safe.
Comments