Reverse T3 is a biologically inactive thyroid hormone; however, it does block the conversion of thyroxine (T4) to triiodothyronine (T3). Higher levels of reverse T3 can decrease the effect of thyroid hormone. While reverse T3 does not act like other thyroid hormones T3 and T4, it may play a role in brain development. Serum reverse T3 levels are helpful in distinguishing between thyroid disease and disease not related to the thyroid gland. Serum reverse T3 is often helpful when total T3, total T4, free T4, and TSH levels provide expected results or further investigation is needed. Because reverse T3 can be altered by illness, it is not useful in hospitalized patients.
Normal Ranges for serum reverse T3:
Decreased rT3 levels in the serum are uncommon. When it occurs, it usually happens in people with hypothyroidism or those being treated with growth hormones or steroids. Elevated rT3 does not specifically cause symptoms, but the thing that caused the increased rT3 level may cause its own symptoms.
Some specific causes of low reverse T3 are:
Elevated reverse T3 (rT3) levels can be caused by almost any serious or prolonged illness. Low blood oxygen levels strongly increase reverse T3 levels in the serum. People with severe malnutrition (especially a lack of carbohydrates), severe diabetes, kidney, or liver disease have increased levels of rT3. Elevated rT3 does not specifically cause symptoms, but the disease that caused the increased rT3 level causes its own symptoms.
Some specific causes of high reverse T3 are:
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