Principles and Practical tips for Reverse T3, FT3, FT4

This post follows up on several recent posts on the topic of Reverse T3 (RT3) and our thyroid hormone conversion enzymes, the three deiodinases. Here I'm providing some practical tips about Reverse T3 testing, test interpretation, and where we should be focusing our attention. In these posts, I aim to improve thyroid therapy by debunking …

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Individual thyroid ranges are 38-68% the size of the lab reference range

We've known since at least 2002 that being within "normal range" is never good enough when it comes to thyroid hormone blood tests. An important set of articles has taught us that each human being has an optimal range for TSH, Total T4 and Total T3 that is far less the width of the population-wide …

Continue reading Individual thyroid ranges are 38-68% the size of the lab reference range

The Abbott Free T3 test kit recall of 2018-2019

Recently I came across the information about the Free T3 lab test assay kit recall by Abbott Laboratories announced in late 2018. The recall was initiated in October 2018 and the FDA record was published in February 2019. The reason they list is the potential for a mistakenly lower Free T3 test result. "Samples tested …

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Thyrotoxicosis can occur with high or normal TSH?

Table 17.1 in Braverman & Cooper's 2013 chapter in Werner & Ingbar's The Thyroid textbook, 10th edition, lists many causes of thyrotoxicosis. The only time the TSH _hormone_ is listed as a cause of thyrotoxicosis is in the case of "Inappropriate TSH hypersecretion." If thyrotoxicosis can occur when TSH is inappropriately _high_ or non-suppressed in …

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Thyrotoxicosis? Many factors can lower TSH

Many substances and health factors can, independently of thyroid hormones, lower TSH secretion significantly. These factors are not listed in Braverman & Cooper's chapter on thyrotoxicosis in Werner & Ingbar's The Thyroid textbook, 10th edition 2013, because their chapter avoids defining the syndrome by a low TSH. Nevertheless, these TSH-lowering factors should always be mentioned …

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Abbott Laboratories’ reference range normalizes lower Free T3

In late 2018, in Ontario, Life Labs changed its reference range for Free T3 (Triiodothyronine) thyroid lab tests. In our closed Canadian Thyroid Support Group where patients share their lab results and therapy progress over time, this particular Free T3 test has been behaving strangely so far, especially comparing changes from the old assay to the …

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Interpreting Free T3 and Free T4 in therapy

Hypothyroidism is a thyroid hormone insufficiency, so it's only logical to measure the success of therapy by the goal: T4 and T3 thyroid hormone sufficiency. Especially T3 sufficiency, the active hormone. Lab tests like Free T3 and Free T4 can indicate "relative" T3 and T4 sufficiency in bloodstream ... but one has to carefully interpret …

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