What are my key thyroid function tests?
The most sensitive is TSH.
For example, if you find a patient with Hashimoto
and there was decreased levels of T3, T4,
what are you going to measure?
TSH and you find that to be elevated.
What if your patient had secondary hypothyroidism?
That means that the anterior pituitary is
not functioning properly.
Your TSH levels will be decreased, thus T3,
The TSH levels allow you to ask if a change
in thyroid hormone is being driven by the
For example, if T4 is low and TSH also low
then where’s my underlying issue?
Not in the thyroid, it is in your anterior
Free T4 – directly measures the free hormone.
Very sensitive, bypasses effects of disease
and drugs on thyroid binding globulin levels.
We’ll talk more about TBG.
Thyroid binding globulin would be the binding
protein that’s being synthesized and released
by the liver, influenced by the hormone estrogen
that we’ll talk about later in pregnancy.
What does total mean to you?
It’s a concept.
Free plus bound.
Free plus bound is total.
When you have total, which one of those components
makes up majority of your total?
Not the free.
It’s the bound.
So, total means free and bound.
Always keep that in mind.
That will make your life so much easier later
when we talk about pregnancy.
So, total T4 greater than 99% protein bound…
What’s the name of that protein?
Thyroid binding globulin.
Coming from where?
From the liver.
Influenced by whom? Estrogen.
I’ve done that plenty.
Need to take into account TBG status and thus,
helps in diagnosis of hyperthyroidism, hypothyroidism
only under conditions of normal TBG levels.
So, you need to make sure that you rule out
properly where or not there is increased levels
And that will be important for you.
So, what is TBG?
Thyroid binding globulin binds T4 and T3,
comes from the liver.
It is then influenced by estrogen.
Now things that you’re paying attention
to what the type of patient who increases
the levels of TBG include pregnancy or contraceptive
pills with, that may contain estrogen.
And decreased by androgens, glucocorticoids,
severe illness, malnutrition and protein-losing
Those are decreased in TBG.
You want to make sure that you know about
those patients and you want to know about
those patients in which you find increased
TBG, those indications where you have a patient
and an increased estrogen status.