You’ve been gaining weight despite eating well. You’re cold all the time. Your energy has disappeared, your hair is thinning, and your brain feels like it’s wading through fog. You ask your doctor to check your thyroid, and they run a TSH. It comes back at 3.5. “Perfectly normal,” they say.
But is it?
What TSH Actually Tells You (And What It Doesn’t)
TSH, or thyroid-stimulating hormone, is the standard screening test for thyroid function. It’s produced by your pituitary gland in your brain and tells your thyroid how much hormone to make. When your thyroid is underperforming, TSH rises as your brain tries to push harder. When your thyroid is overactive, TSH drops.
It’s a useful starting point. But here’s the problem: TSH is an indirect measure. It tells you what your brain thinks is happening. It doesn’t tell you what’s actually reaching your cells, how well your body is converting thyroid hormones, or whether your immune system is quietly attacking your thyroid gland.
Relying on TSH alone is like checking the thermostat on your wall without looking at whether the heater is actually working. The thermostat might read “fine” while you’re sitting in a cold room.
Thyroid Hormones Fluctuate
Another piece that’s often overlooked is that thyroid hormones naturally fluctuate. TSH varies throughout the day, across seasons, and in response to stress, illness, and changes in body composition. A single TSH reading is a snapshot, not a trend.
This is why I track thyroid markers over time rather than making decisions based on one isolated result. A TSH of 3.5 today might have been 1.8 a year ago. That upward trend is clinically meaningful, even if both values fall within the reference range.
Why a Full Thyroid Panel Matters
When a patient comes to me with symptoms suggestive of thyroid dysfunction, I don’t stop at TSH. I run a full panel that includes:
TSH as the screening marker
Free T4 (fT4) to see how much inactive thyroid hormone is circulating
Free T3 (fT3) to see how much active thyroid hormone is available to your cells
Thyroid antibodies (anti-TPO and anti-thyroglobulin) to check whether the immune system is involved
This distinction matters enormously. Free T3 is the hormone that actually does the work at a cellular level. You can have a normal TSH and a normal fT4, but if your body isn’t converting T4 into T3 efficiently, you will feel hypothyroid. And if we’re not measuring fT3, we’ll never know.
The Antibody Piece, Especially Around Middle Age
Thyroid antibodies are perhaps the most underappreciated part of the thyroid story. Hashimoto’s thyroiditis, an autoimmune condition where the immune system gradually attacks the thyroid gland, is the most common cause of hypothyroidism. And it’s far more prevalent in women, particularly as they approach middle age.
Here’s what makes Hashimoto’s tricky: it can be present for years before TSH becomes abnormal. Antibodies can be elevated long before the gland has been damaged enough to shift your TSH out of range. If you only test TSH, you’ll miss the early window entirely.
Why does this matter? Because catching elevated antibodies early gives us the opportunity to intervene. We can address modifiable factors like gut health, inflammation, stress, nutrient deficiencies (particularly selenium, zinc, and vitamin D), and make meaningful changes before the gland is irreversibly damaged.
The Perimenopause Connection
Thyroid dysfunction and perimenopause share a significant overlap in symptoms: fatigue, weight gain, mood changes, brain fog, hair loss, poor sleep. It’s not uncommon for women in their 40s to be told their symptoms are “just hormonal” when in fact their thyroid is part of the picture, or vice versa. Sometimes it’s both.
This is why, when a woman in midlife presents with these kinds of symptoms, I look at the full picture. Thyroid function, hormonal status, metabolic markers, and nutrient levels all play into one another. Treating one while ignoring the others is like patching one tyre when three are flat.
Why Tracking Over Time Matters
A single set of thyroid results is helpful, but it’s the trend that tells the real story. I encourage my patients to have their thyroid markers checked at regular intervals so we can see how things are moving. A TSH that’s slowly creeping upward, antibodies that are gradually climbing, or an fT3 that’s drifting lower over time. These patterns are clinically significant and they’re invisible if you only test once.
This is what investigative blood analysis is about. Not just asking “is this number in range?” but asking “what is this number doing over time, and what does that mean for this person?”
The Bottom Line
If you’re symptomatic and your doctor has only tested TSH, you haven’t had a full thyroid assessment. A single TSH value doesn’t capture the complexity of how your thyroid is functioning, whether your immune system is involved, or whether your body is efficiently using the hormones it produces.
Your symptoms are valid. And sometimes, the answer is hiding in the tests that weren’t ordered.
Dr Robyn Bradfield is the founder of Bloodfields, a virtual investigative blood analysis practice. If you’d like a comprehensive thyroid assessment that goes beyond TSH, you can book through our website.