fT3:rT3 - Free T3 to Reverse T3 ratio
The ratio of Free T3 to Reverse T3 can help understand what’s happening at the tissue level because it helps determine how effective thyroid conversion from T4 into active T3 is.
The Free T3 to Reverse T3 ratio is used to help determine whether there are issues with thyroid hormone conversion. A high or optimal ratio of Free T3 to Reverse T3 isn’t considered clinically significant. A low Free T3 to Reverse T3 is a sign of Thyroid Hormone Conversion Syndrome, a situation where the peripheral conversion of T4 into the more metabolically active T3 is decreased.