HOW USEFUL IS A REVERSE T3 TEST IN DIAGNOSING HYPOTHYROIDISM?

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4. How useful is a reverse T3 test in diagnosing HYPOTHYROIDISM?

I

believe the test is of virtually no value in diagnosing hypothyroidism, if by

hypothyroidism we mean a thyroid hormone deficiency. When the thyroid gland

produces too little T4 and T3, less of these two hormones are available. The

vast bulk of what the thyroid gland produces and releases into the blood is T4.

With a lower-than-usual amount of T4 available, it’s likely that more of

it will be converted to T3 rather than reverse T3. This presumably results from

a need to keep the T3 high enough to maintain effective cell function. Also

presumably, reverse T3 production from T4 will decrease to some degree. As a

result, in moderate-to-severe hypothyroidism we might find low T4,

low-to-mid-range T3, and a low reverse T3. However, as far as I know, no

researchers have shown that this lab result pattern is useful for diagnosing

hypothyroidism.

This

pattern in hypothyroidism is only a conception based on principles. But in

actual practice, I’ve rarely seen this pattern in hypothyroid patients. I

believe the reason is that when the TSH and thyroid hormone levels are in

range, their levels vary (as Japanese researchers say) “dramatically

every thirty minutes or so.” There is no correlation from thirty-minute

period to thirty-minute period, day-to-day, and week-to-week.

In

my opinion, the reverse T3 has served us best in diagnosing a condition that

has a variety of names: “euthyroid sick syndrome,” “low T3

syndrome,” and “non-thyroidal illness syndrome.” The word

“euthyroid,” of course, means that the person has in-range TSH, T4,

and T3 levels. In this condition, the hypothalamus secretes less TRH, the

pituitary secretes less TSH, and less thyroid hormone is transported into

cells. Also, the enzyme called “5-prime deiodinase,” which converts

T4 to T3, becomes far less active. Another enzyme, “5 deiodinase”

(no “prime” as a modifier) becomes more active and converts more T4

to reverse T3.

The

words “sick syndrome” is somewhat misleading. That term is used

presumably because the condition was first identified in sick people, such as

anorexics and hospitalized patients in critical condition. Studies showed that

the patients had steeply raised cortisol levels. It’s their high cortisol

levels that inhibit the enzyme (5-prime deiodinase) that converts T4 to T3.

I’ve

found no evidence that this condition becomes chronic, as Dr. Dennis

proposed. Instead, the research literature shows that within a week or two, TSH

secretion increases and 5-prime deiodinase escapes the inhibition by cortisol.

This happens even though the person’s cortisol levels remain high. For

example, if the person undergoes prolonged treatment with prednisone, within a

week or two, the TSH level returns to its previous level and 5-prime deiodinase

becomes normally active again.

Old

studies show that on average, most people convert more than 50% of their T4 to

reverse T3; correspondingly, they convert less than 50% of T4 to the

metabolically active hormone T3. And the levels of reverse T3 fluctuate up and

down through the day. Because of this, I’m never confident of coming to a

conclusion that someone has a problem with high reverse T3, not unless the

person has had multiple measures of the reverse T3 over a 24-hour period. Like

the TSH, free T4, free T3, reverse T3 levels vary dramatically every 30 minutes

or so. Depending on when a person’s blood is drawn or saliva taken.

Sometimes the levels will vary enough so that a clinician will give the patient

a different diagnosis from the one that he or she would have given 30-minutes

before or after the blood or saliva sample was taken.

So

blood levels vary rapidly. Because of this, I don’t believe the reverse

T3 or the other lab tests in general are very useful. However, I do believe the

reverse T3 is useful under one circumstance: when we have enough measures to

get averages over time, and when the levels are regularly way out of range. So,

in my view, the reverse T3 can be useful, but I think its usefulness is

limited, which is true of the TSH and other thyroid hormone levels.

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