A visual index of thyroid function.

A visual index of thyroid uptake (VITU) is introduced as a qualitative measure of thyroid trapping. This index is determined from the 20-minute 99mTc-pertechnetate scan by visually comparing the relative tracer uptake between the thyroid and salivary glands. Three categories are defined: low, normal and elevated. The VITU correctly identified the functional status of the thyroid in 94% of 123 patients studied and agreed with the 24-hour radioiodine uptake (RAIU) in 89%. The VITU is a very simple but highly accurate, reliable and reproducible test. It was primarily designed to complement other tests of thyroid function by contributing qualitative information about the thyroidal trapping mechanism, but it can also be useful in confirming blood tests of thyroid function in cases in which one would prefer to avoid 131I administration for RAIU studies.