What Total T4 and Total T3 Actually Measure
Let’s break this down without the medical jargon.
Your thyroid produces two main hormones: T4 (thyroxine) and T3 (triiodothyronine).
T4 is mostly inactive — think of it as storage. T3 is the active form that powers things like metabolism, energy, and body temperature.
So when we talk about Total T4 and Total T3, we’re talking about the total amount of those hormones in your bloodstream — both the free (usable) and bound (stored) forms.
Here’s how I explain it to clients:
“Imagine your thyroid as a warehouse. T4 is the inventory waiting to be shipped. T3 is what’s actually leaving the shelves and fueling your body. Your total thyroid hormones tell us how stocked your warehouse is — but not necessarily how well your team is moving the product.”
That’s why these tests matter even if you’ve already checked your “free” levels — because sometimes, the warehouse is full, but the system’s not delivering what you need.
Why These Labs Matter
Your Total T4 and T3 levels tell us how much raw material your thyroid is making — and whether your body’s able to convert that supply into usable energy.
If Total T4 is low, your thyroid might not be producing enough hormone to begin with.
If Total T3 is low, your body may be struggling to convert T4 into active T3 — something that happens all the time with stress, inflammation, or nutrient deficiencies.
And if they’re both normal but you still feel sluggish or anxious?
It could be that too much of your hormone is “bound up” — not available to your cells — often thanks to things like high estrogen or poor liver detox.
Your thyroid doesn’t operate in isolation. It’s part of a bigger hormonal orchestra.
If one section’s offbeat — cortisol, estrogen, blood sugar — the whole rhythm can shift.
Understanding Your Numbers
Here’s what typical reference ranges look like (these can vary slightly by lab):
| Test | Typical Range | What It Means |
|---|
| Total T4 (Thyroxine) | 5.0–12.0 µg/dL | Reflects total circulating thyroxine — your thyroid’s storage hormone. Low = underproduction or poor conversion. |
| Total T3 (Triiodothyronine) | 80–200 ng/dL | Shows total triiodothyronine (active + bound). Low = sluggish conversion or chronic stress. |
⚠️ Note: “Normal” doesn’t always mean optimal. Your body, symptoms, and Free T3/T4 levels matter too. Always review your results with a provider who looks at patterns, not just ranges.
Factors That Affect Total T3 and T4
Your thyroid’s story is never just about one number.
Here are the big influences I see time and again:
Chronic stress — High cortisol slows T4-to-T3 conversion, so you might have plenty of T4 but low active hormone.
Nutrition — Low selenium, zinc, iron, or protein can stall thyroid hormone production and conversion.
Estrogen and liver function — Both impact thyroid-binding globulin (TBG), which changes your total levels even if production is fine.
Medications — Birth control pills, steroids, and beta blockers can alter conversion or binding proteins.
Inflammation and illness — The body conserves energy when stressed or inflamed, temporarily lowering active thyroid hormone.
I’ve seen women push through workouts, under-eat, and over-caffeinate — then wonder why their T3 levels drop.
It’s not lack of discipline. It’s physiology saying, “I need recovery, not restriction.”
Supporting Healthy Thyroid Function Naturally
When it comes to thyroid health, consistency beats intensity.
Start small, but stay steady.
Here’s what I recommend to nearly everyone working on thyroid balance:
🍳 Eat enough protein — It’s the backbone of hormone production.
🌰 Add selenium, zinc, and iodine through foods like eggs, seafood, and Brazil nuts.
🧘♀️ Support your stress response — cortisol and thyroid hormones are dance partners.
🫀 Take care of your liver — it’s where T4 becomes active T3. Whole foods, hydration, and rest matter.
😴 Sleep and recovery — because healing happens when you’re off the clock, not when you’re grinding harder.
Your thyroid doesn’t need extremes — it needs nourishment and safety.
