TSH Test

What this test actually measures

TSH is not a thyroid hormone. That is the first thing worth knowing about it, and it explains most of what follows.

It is made by your pituitary, a gland at the base of your brain, and it is an instruction rather than a product. The pituitary samples how much thyroid hormone is available, and adjusts TSH to ask the thyroid for more or less.

Which produces the counter-intuitive part people trip over constantly. TSH runs in the opposite direction to thyroid function. A high TSH means the pituitary is shouting for more, which suggests an underactive thyroid. A low TSH means it has gone quiet, which suggests an overactive one.

So a TSH result tells you what your pituitary currently thinks about your thyroid hormone supply. That is genuinely useful information, and it is a report on the negotiation rather than a measurement of the goods.

What it is good at, and the two things it cannot do

Let me give TSH its due first, because it earns its place as a screen. It is sensitive, inexpensive, and it detects overt hypothyroidism and hyperthyroidism reliably. If someone has a genuinely failing or overactive thyroid, TSH finds it. That is why it is the standard first test everywhere.

Now the two limits, both structural rather than accidental.

The first is conversion. TSH responds mainly to T4, the storage hormone. Converting T4 into active T3 happens afterwards, in peripheral tissues. So if your gland produces plenty of T4 and your body converts it poorly, the pituitary is satisfied, TSH sits comfortably in range, and the active hormone reaching your tissues is still low. TSH cannot see that, because conversion happens after the point TSH is reporting on.

The second is autoimmunity. Thyroid antibodies typically turn positive years before TSH moves out of range, because the gland has reserve and compensates for a long time. So a normal TSH tells you the gland is currently keeping up. It does not tell you whether something is slowly wearing it down.

There is a third point that is about the range rather than the test. A 2002 study in the Journal of Clinical Endocrinology and Metabolism found each person orbits their own narrow set point, with an individual range roughly half the width of the population range. A TSH of 3.5 in someone who has run at 1.2 for a decade is a real move that both results print as normal.

Where exactly the upper limit belongs has been argued in the literature since at least a 2005 exchange in the same journal, and reviews of subclinical hypothyroidism continue to work through what treating a mildly raised TSH actually achieves. That disagreement is genuine and it is not settled by anything on this page.

One practical warning: biotin, found in hair and nail supplements, interferes with thyroid immunoassays and can shift results in either direction. A 2016 case report described results mimicking Graves disease that normalised once biotin was stopped. Mention your supplements.

Test details

What is measured: thyroid stimulating hormone, in mIU/L.

Sample: blood draw.

Provider: Quest Diagnostics, ordered through Jess's practitioner dispensary.

Fasting: not required. A morning draw is worth being consistent about, since TSH follows a daily rhythm. Mention any biotin supplement, since it interferes with the assay.

Turnaround: results typically within a few business days of the sample reaching the lab.

Order this test.

How the pricing works

I want to be straightforward about this, because lab pricing in the wellness industry frequently is not.

Jess takes no markup on the test itself. The lab cost is passed through exactly as it comes. What you pay is the test cost, the dispensary's service fee, the authorization fee, the collection fee where one applies, a flat handling fee for placing and managing the order, and the card processing cost. The handling fee is the part that is Jess's, and it is flat regardless of how expensive the test is.

That structure is deliberate. A percentage markup on labs creates an incentive to recommend expensive tests, and this way there is not one.

Because every blood test in one order shares a single draw fee, adding a second or third test to the same order costs considerably less than ordering them separately. The full lab menu shows what shares a draw with this one, and the order page itemises every fee before you pay.

Who this test is worth running for

A TSH alone is reasonable as a genuine screen: no symptoms, no family history, just checking. It is cheap and it catches the thing it is designed to catch.

It is the wrong test as a final answer when you have symptoms. If you are tired, cold, gaining weight, losing hair or foggy, ordering a TSH and stopping there answers roughly a third of the question you brought. The full thyroid panel is what addresses the rest, from the same draw.

It is also the wrong test on its own if you have another autoimmune condition or a family history of thyroid disease, since antibodies are what reveal autoimmune activity and TSH stays normal through years of it.

Ordering restrictions

The lab network cannot issue orders to residents of New York, New Jersey, Rhode Island, or Hawaii. New York, New Jersey, and Rhode Island prohibit direct-to-consumer lab testing outright, requiring a treating provider's signature on every requisition. Hawaii is excluded by the network. This is tied to where you live, not where the sample is collected, so it applies to kits as well as draws.

If you live in one of those four states, your doctor can order the same test.

What to do with the result

Compare it against your own history first. Given the individual set point research, where your TSH has been matters more than where it sits in the population range. Line up your old results with dates.

If TSH is clearly raised or clearly suppressed, that is a doctor conversation and it needs the circulating hormones measured alongside to interpret it properly.

If TSH is normal and you still have symptoms, that is not the end of the question. Order free T4, free T3 and antibodies, because those are the parts a TSH structurally cannot answer.

If TSH is mildly raised, what to do about it is genuinely debated rather than obvious, and it depends on your antibodies, your symptoms and your age. Take it to a provider rather than to a supplement.

Read the number alongside what it means. The TSH page goes through the range argument in detail.