Being able to calculate your rT3 Ratio allows you to determine whether an excess amount of reverse T3 hormone is a significant driver to your particular case of hypothyroidism, or the range of symptoms you may be experiencing due to an underactive thyroid.
To refresh yourself on exactly what reverse T3 is, and why this form of the T3 thyroid hormone plays such an important role in hypothyroidism, please click here.
Unfortunately, Reverse T3, or rT3 is something that is largely ignored by medicine at this present time. Yet, once its role in hypothyroidism and other thyroid disorders is understood, so too can one treat this condition more effectively.
Examples Of How To Calculate Your rT3 Ratio
Before working out this ratio, it's important to ensure that the units of measurement used in the test results are the same for the reverse T3 reading, as well as for the FT3 (free T3). Some labs use one system and others use another system of measurement units.
There are two main units used, which are the metric (here the units are pg/mL), or the molecular weight system (its units of measurement are pmol/L).
Basically, we want to establish whether your body has about 20 times the amount of FT3 compared to the amount of rT3, as this has generally been found to be associated with good health. In essence, this is what makes the rT3 Ratio such a useful tool.
Because labs use these two different ways of reporting their results, you may find your FT3 (free T3) reported as a figure in the hundreds, e.g. 325. Or it may be reported as a smaller figure, e.g. 3.2.
In a similar fashion, the labs may present the rT3 figure as something like 220, or it may appear as 22.
(Yes, I know; it's enough to drive you crazy! But, simply follow the formulas presented below, and hopefully most of you will be able to figure out your rT3 Ratio!)
The Mathematical Rules For Determining A 'rT3 Ratio'
Depending, therefore, on how the results of the thyroid tests are given by the lab in question, we do the following things:
• Remember, to figure out your rT3 Ratio, you'll be working with two separate bits of data – your rT3 result, and your FT3 result.
• If the result for FT3 is given as a smaller number e.g. 3.2, then multiply that 3.2 by 100.
• But this multiplication may need to be modified, depending on how your rT3 data is presented.
• So, if your rT3 figure is simultaneously given as a figure in the hundreds e.g. 220, then your FT3 figure above (presented by the labs as a smaller number – in this example: 3.2) is not multiplied by 100, but by 10 instead.
• Once you've made those decisions, and done the appropriate multiplication of your FT3 result by either 100 or 10, you now divide the resultant FT3 figure by the rT3 figure, which presents you with your 'Reverse T3 Ratio'.
Please understand that the basic rules given above are simply not going to work for all the variations of test results available on a global level.
Having acknowledged that these examples won't neatly cover every lab's results, let's at least do a few sample calculations, and hope that the figures you've been given do fall into the sort of ranges discussed here.
EXAMPLE 1:
In this first example, let's assume that your FT3 is 325, and your rT3 is 22.
Here, your FT3 is a figure in the 100's, and your rT3 figure is not in a decimal version (e.g. 2.2)
This is the easiest format from which to determine your rT3 Ratio, as it now becomes a simple division of one figure into the other, without the need to mathematically modify them – as will be shown in further examples below.
So, according to the rules given above, we now simply divide the 325 by 22 = 14.8. This is your rT3 Ratio!
Because that calculated ratio is less than 20 (i.e. 14.8 in this example), this is interpreted as meaning you most likely do have a rT3 problem
In this particular example, let's assume that your FT3 result is reported as 3.45, and your rT3 as 14.
Remember, since your FT3 is not stated as a figure in the hundreds (in this example it is 3.45), the rule given at the beginning of this discussion states that it now needs to be multiplied by 100.
So, we get: 3.45 x 100 = 345
Then we divide that new figure (345) by the rT3 figure, which was given as 14 (not in a decimal format i.e. 1.4, and hence no further need to modify it)
Hence, we simply go ahead and get: 345 divided by 14 = 24.6.
This 24.6 is your rT3 Ratio, and since it is above 20, it would suggest that you do not have a rT3 issue blocking your overall thyroid function within your system - from a systemic perspective.
Let's look at another variation-on-a-theme of how these lab results could be presented to you.
It is possible that this time the rT3 is given as a large number, e.g. 305, while your FT3 is also given as a large number, e.g. 375
In this case we do the following:
Since the rT3 figure is presented in the hundreds (i.e. 305), we now only multiply the FT3 figure by 10 (instead of the 100 used in the previous example above)
So... we get: 375 x 10 = 3750
This figure is then divided by the rT3 figure of 305
i.e. 3750 divided by 305 = 12.3.
Again, this is your rT3 Ratio, and because it is less than 20, it would indicate that you do have a reverse T3 issue as at least a major cause to your treatment resistance, or the continuation of your hypothyroidism symptoms, despite treatment.
Here we look at a final illustration of how these various FT3 and rT3 figures may be presented to you by the labs.
Let's assume your FT3 figure is 3.1, and your rT3 figure is 210
Firstly, since the FT3 is not given as a figure in the 100's (it's given here as 3.1), it therefore becomes necessary to multiply this FT3 number by 100.
However, note that the rT3 figure is given in the 100's (i.e. 210), so according to the above rules, the FT3 number now needs to be additionally multiplied by 10!
(Yes... I know. It's enough to want to either give up, or tear your hair out!)
However, let's assume you are brave enough to hang in there, then, firstly, to deal with the way the FT3 is presented (i.e. 3.1), we get: 3.1 x 100 = 310
Next, to deal with the way the rT3 is presented, we need to concurrently do that extra multiplication on the figure obtained thus far (i.e. 310), and so now we get: 310 x 10 = 3100
Now we divide this twice multiplied number (i.e. 3100) by the rT3 number of 210.
This gives us: 3100 divided by 210 = 14.8. This is your rT3 Ratio.
Because it is less than 20, it could well indicate an excess rT3 blockage effect within our system as the cause of your hypothyroidism symptoms.
I get a sense that for many of you, your eyes have glazed over by this point, and your mind has gone completely numb! Maths is not my strong point either, and I don't expect it to be yours!
However, by carefully looking at how your lab figures are presented, you can then choose from these examples as to which formula you'll need to use in order to work out your rT3 Ratio.
But, even when you have that result, let's be very clear that the rT3 Ratio is not some God-given, infallible mathematical figure which will absolutely, definitely prove or disprove you have a hypothyroid problem or not.
It's exactly that: just a tool, and it is critical that any result obtained via that tool is put into the larger context of other lab results (and their more 'alternative' interpretation!).
So, remember: above all, any lab results always need to be secondary to the reality of your overall symptom presentation.
In other words, symptoms have precedence; not mathematical calculations, or bits of paper coming out of some laboratory machine!
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