RT3 Overview Reverse triiodothyronine (reverse T3, or RT3) is a molecule that is an isomer of triiodothyronine (T3). It is derived from thyroxine (T4) through the action of deiodinase. RT3, unlike T3, does not stimulate thyroid hormone receptors. However, rT3 binds to these receptors, thereby blocking the action of T3. Reverse T3 (RT3) is what is made when the “wrong” iodine atom is removed from T4; it’s a “mirror image” molecule to T3 and is not bio-active. This in itself is not a problem, the problem is that in excess it fits into the T3 receptors and gets stuck there blocking the action of T3 on the body. This means that your body doesn’t respond properly to T3 leading to hypothyroid symptoms despite a within range TSH and within range T3 and T4 levels in the body. This is what we refer to as “Tissue Resistance to Thyroid Hormone”. Causes The prolonged use of T4 only thyroid meds – Synthroid, Levoxyl, Levothyroxine, Unithroid, Eltroxin, Levaxin, Norton, Eutrosig, Oroxine and others. Beta Blockers High iron Low iron High cortisol Low cortisol Amiodarone Iodinated contrast media Lithium Under or improper treatment of Hypothyroidism Long Term Illness including viral load Glucose over 140 Low Calorie Diet Below 30G daily Carbohydrate Diet Symptoms Continuing hypothyroid symptoms while on at least 3 grains of desiccated thyroid See the section on hypothyroid symptoms Free T4 labs results above midrange Any time FT4 is higher in range than FT3 in it’s range FT3 that will not rise in spite of increased natural thyroid Testing TSH – to check for possible pituitary issues (low iron will also suppress TSH even with low thyroid levels as will low cortisol) Free T4 (FT4) – the stored thyroid hormone Free T3 (FT3) – the active thyroid hormone Reverse T3 (RT3) - TPO anti-bodies (thyroid peroxidase) – to check for Hashimoto’s Thyroiditis TgAb (thyroglobulin antibodies) It is then the ratio of RT3 and FT3 that need to be determined. A ratio below 20 shows an RT3 issue. You will also need to get a complete iron panel with ferritin. See the section on iron. Treatment Treatment for RT3 starts by addressing the reason for the RT3. This could mean altering cortisol, iron or medications. The treatment for RT3 is Cytomel (T3) in slowly increasing doses until the T3 receptors have been cleared. The starting dose for T3 is usually 12.5 mcg divided into two dose (first thing in the morning and in the early afternoon) additional doses are add in 5 – 7 days so that you will eventually be dosing T3, four times day, 4 hours apart with the last dose at bedtime. Most will need between 75-100mcg of T3. The body will not tolerate higher doses of T3 without the reason for RT3 being addressed. Examples of How to Calculate FT3/RT3 and TT3/RT3 Ratios Which example to use depends on the units of the test used by your lab. I have listed several common sets of units. Free T3 and RT3 A healthy FT3/RT3 ratio is 20 or greater. FT3 pmol/LRT3 pmol/L These results need to be changed so that the ratio is correct. Multiple FT3 by 1000 then divide the result by RT3.Ex. FT3 5.4, RT3 567(5.4 × 1000) ÷ 567 = 9.5 FT3 pmol/LRT3 nmol/L These results will give the correct ratio. Divide FT3 by RT3.Ex. FT3 5.9, RT3 0.385.9 ÷ 0.38 = 15.5 FT3 pg/mLRT3 pg/mL These results need to be changed so that the ratio is correct. Multiple FT3 by 1000 then divide the result by RT3.Ex. FT3 2.6, RT3 258(2.6 × 1000) ÷ 258 = 10 FT3 pg/dLRT3 ng/dL These results will give the correct ratio. Divide FT3 by RT3.Ex. FT3 403, RT3 25, 403 ÷ 25 = 16 FT3 pg/dLRT3 pg/mL These results need to be changed so that the ratio is correct. Multiple FT3 by 10 then divide the result by RT3.Ex. FT3 397, RT3 474(397 × 10) ÷ 474 = 8.3 FT3pg/mL RT3 ng/dL These results need to be changed so that the ratio is correct. Multiple FT3 by 100 then divide the result by RT3.Ex. FT3 2.9, RT3 23(2.9 × 100) ÷ 23 = 12.6 FT3 pmol/L RT3 ng/dL These results need to be changed so that the ratio is correct. Divide FT3 by 0.0154 then divide the result by RT3.Ex. FT3 4.5, RT3 30.3(4.5 ÷ 0.0154) ÷ 30.3 = 9.6 Total T3 and Reverse T3 The ratio should be greater than 10 for T3/RT3. T3 ng/dLRT3 pg/mL These results need to be changed so that the ratio is correct. Multiple T3 by 10 then divide T3 byRT3.Ex. T3 123, RT3 295(123 × 10) ÷ 295 = 4.2
Posted on: Thu, 01 Aug 2013 11:32:16 +0000
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