Interpreting Thyroid Labs

[Dr Justin Saya MD]

When evaluating ratios, one must always take into account the units of measurement of the two components of the ratio (which will typically be different units). For example, through LabCorp, free T3 is reported in units of pg/mL (range 2.0 - 4.4 pg/mL) and reverse T3 is reported in units of ng/dL (range 9.2 - 24.1 ng/dL).

So, when saying, as the STTM folks always tout, that a 20:1 ratio is ideal folks have to make sure to convert to the same units. However, the "calculator" on the STTM site ( http://www.stopthethyroidmadness.com/rt3-ratio/ ) that calculates these ratios is flawed (it doesn't calculate correct ratios...it even states it is a beta calculator...I've had some patients rely on that calculator and come to false conclusions). You can even verify it miscalculates by converting units manually and calculating the ratios or by using the conversion calculator they suggest:

http://www.mens-hormonal-health.com/hormone-unit-conversion-calculator.html

Jackie Treehorn - your Free T3 : 4.0 pg/mL -- (upper end of range 2.0-4.4 pg/mL) compared to your reverse T3 : 10.6 ng/dL (lower end of range 9.2 - 24.1 ng/dL) is indeed a GOOD ratio...you want free T3 upper range with reverse T3 lower range.

HOWEVER, when converting units:

Free T3 4.0pg/mL converts to 0.4 ng/dL, then when plugged in to a ratio with reverse T3 at equivalent units (pg/mL) one gets:

Free T3: reverse T3 = 0.4 ng/dL : 10.6 ng/dL = ratio of 0.037.

Works the same if you just convert the units to both be pg/mL --> reverse T3 10.6 ng/dL converts to 106 pg/mL. And recall free T3 is already in pg/mL units at 4.0 pg/mL. Thus, the ratio:

Free T3: reverse T3 = 4.0pg/mL : 106 pg/mL = ratio of 0.037.

I think the ratio "theory" (and especially the faulty calculator) along with the complexity of unit conversion cause many folks more confusion than good when attempting to evaluate these numbers.

For sanity's sake, when evaluating these ratios, follow this principle:

You want Free T3 on UPPER end of range generally, with reverse T3 on LOWER end of range generally...but there are MANY other layers of complexity just as with the sex hormones.

 

[Jackie Treehorn]

Thanks for clarifying Dr. Saya. I should have noticed the different units of measurement.

 

[Dr Justin Saya MD]

No worries Jackie!

Perhaps Chris may be able to further clarify (if he spends some time over there) what exact units/measurements the STTM folks are always referring to when they say the "20:1 ratio for free T3:reverse T3" as it doesn't work out logically with standard units of measurement. That's why I think it's easier for folks to think in general terms about "where" the levels are without adding the extra complexity (read confusion) of calculating theoretical ratios with variable units of measurement.

 

[gallan]

Got all the secondary labs back. Looks like Reverse T3 is right at the upper limit (25) and Vitamin D3 is low.
Just some quick web research indicates that my low ferritin could be to blame for the high Reverse T3.
Started supplementing with 6000 IU a day of D3 and apparently the D2 test means nothing?


Thyroid
T3 REVERSE, LC/MS/MS 25
8-25 ng/dL


T3, FREE 3.4
2.3-4.2 pg/mL


T4, FREE 1.2
0.8-1.8 ng/dL


THYROGLOBULIN ANTIBODIES <1
< OR = 1 IU/mL


THYROID PEROXIDASE ANTIBODIES 2
<9 IU/mL


TSH 1.60
0.40-4.50 mIU/L


Blood Health
Iron
% SATURATION 49 Apr/2016
15-60 % (calc)


FERRITIN 35
20-380 ng/mL


IRON BINDING CAPACITY 472
250-425 mcg/dL


IRON, TOTAL 229
50-180 mcg/dL




Vitamins


VITAMIN D, 25-OH, D2 <4


VITAMIN D, 25-OH, TOTAL 38 30-100 ng/mL

 

[John O'Connor]

I used Dr. Saya's calculator to convert Reverse T3 from 25 (ng/dL) to 250 (pg/mL). So ratio = 3.4 : 250 = .0136
This doesn't make sense. Even if reverse T3 was at the low end of range (8 -25) the ratio would still be less than .20.

Can someone show me the correct way to convert these, so this ratio makes sense.

I'm a little confused why the ratio matters. Your Free T3 looks ok, slightly above the middle of range. So, is your body simply recognizing that there is enough, and thus (to save energy) as this article suggests - simply turning the rest into reverse T3? http://thyroid.about.com/od/t3treatment/a/Reverse-T3-triiodothyronine-RT3-Thyroid.htm

It would make sense to be concerned if your Free T3 was low, but I'm not sure what to make of this scenario.

http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/9405
Based on this article - I'm guessing it just means your total T4 was high, and since you have enough free T3, its simply converting the rest to the inactive form, aka reverse T3.

I'm looking forward to see what Chris and Dr. Saya think. Would prescribing Free T3, as opposed to synthroid (T4) be the strategy now? If so - what would be the goal? To move FREE T3 from current 3.4 level, closer to 4.2? Range =
(2.3-4.2 pg/mL)

 

[CoastWatcher]

I used Dr. Saya's calculator to convert Reverse T3 from 25 (ng/dL) to 250 (pg/mL). So ratio = 3.4 : 250 = .0136
This doesn't make sense. Even if reverse T3 was at the low end of range (8 -25) the ratio would still be less than .20.

Can someone show me the correct way to convert these, so this ratio makes sense.

I'm a little confused why the ratio matters. Your Free T3 looks ok, slightly above the middle of range. So, is your body simply recognizing that there is enough, and thus (to save energy) as this article suggests - simply turning the rest into reverse T3? http://thyroid.about.com/od/t3treatment/a/Reverse-T3-triiodothyronine-RT3-Thyroid.htm

It would make sense to be concerned if your Free T3 was low, but I'm not sure what to make of this scenario.

http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/9405
Based on this article - I'm guessing it just means your total T4 was high, and since you have enough free T3, its simply converting the rest to the inactive form, aka reverse T3.

I'm looking forward to see what Chris and Dr. Saya think. Would prescribing Free T3, as opposed to synthroid (T4) be the strategy now? If so - what would be the goal? To move FREE T3 from current 3.4 level, closer to 4.2? Range =
(2.3-4.2 pg/mL)

In two recent posts, on two separate threads, Dr. Saya addressed the thyroid ratio. He noted that the calculator on the "Thyroid Madness" site was flawed in its design. He also suggested that patients can turn themselves inside out chasing a metric, and that for the sake of common sense, one would want to see T3 in the upper end of the scale and RT3 at the lower end of the scale. This is, of course, a great simplification, but until Chris, the one member of the Forum with a better grasp of this situation, weighs in, I urge all to simplify their lives with Dr. Saya's common sense advice.

 

[John O'Connor]

Could Vitamin D & Iron ultimately be the problem? Will Reverse T3 fall if these are corrected?

http://www.thyroidchange.org/our-blog/qa-doctor-series-thyroid-resistance-introducing-t4-medication-and-free-t3reverse-t3-ratios-answer-by-david-borenstein-md

"* Dealing with nutritional deficiencies and imbalances, particularly in the areas of B vitamins, tyrosine, selenium, iodine, Vitamin D, and iron. "

As for the ratios - this article explains how to calculate it.
http://www.holistic-hypothyroidism-solutions.com/rt3-ratio.html

In your case the correct ratio = 340/25 = 13.6 and since this is less than 20 you have an issue.
(I multiplied 3.4 x 100 and left the Reverse T3 value of 25 alone.)

In essence to get to 20 with a Free T3 of 3.4, your Reverse T3 would have to be 17 or lower. 340/17 = 20.

 

[Dr Justin Saya MD]

Aha...so they arbitrarily multiply free T3 by 100 to get the >20 ratio...

Easier (and less error prone) just keeping the free T3 and reverse T3 as is (without adjusting or arbitrarily multiplying X 100) and have ratio >0.20 ...but hey, just my 2 cents.

 

[HarryCat]

Aha...so they arbitrarily multiply free T3 by 100 to get the >20 ratio...

Easier (and less error prone) just keeping the free T3 and reverse T3 as is (without adjusting or arbitrarily multiplying X 100) and have ratio >0.20 ...but hey, just my 2 cents.

To my mind your 2 cents is worth at least $10. Very much appreciate your commentary on the this forum.