Thyroid Testing Ratios Analysis

By entering your annual thyroid-related testing data (these data are not collected by ARUP), ratios between different thyroid test volumes are calculated.

Ratio Explanation Rationale
FT4/T4 Shows the rate at which free T4 test is ordered relative to all T4-related testing (i.e., FT4 T4, TT4)
• This is our proposed indicator of “better” test utilization.
• Free T4 is generally recommended over total T4 as the test of choice in thyroid workup.
• Example, a FT4/T4 ratio of 0.80 would suggest that, out of 100 T4-related tests ordered, 80% of the time free T4 (generally considered the ‘better’ test) was ordered instead.
T3U/TSH Shows the rate at which T3 Uptake test is ordered relative to TSH
• This is our proposed indicator of “poor” test utilization.
• TSH is generally used as the initial test in thyroid workup.
• T3U is widely considered by experts to be a thyroid test of very little clinical value.
• T3U/TSH indicates how often T3U is used as part of the thyroid workup. For example, a T3U/TSH ratio of 0.5 would suggest that for every 100 TSH ordered, 50% of the time a T3U would be ordered as well.
T4/TSH Shows the rate at which T4 (i.e., FT4, TT4) is ordered relative to TSH
• TSH is generally used as the initial test in thyroid workup, whereas FT4 and/or TT4 are commonly ordered concurrently with TSH, or as part of the follow-up.
• Although it’s theoretically possible for this value to be greater than one, we expect T4 tests to be ordered less frequently relative to TSH.
T3/TSH Shows the rate at which T3 (i.e., FT3 or TT3) is ordered relative to TSH
• T3-related tests are often down as follow-ups to TSH and T4 (i.e., FT4, TT4) testing
• Although it’s theoretically possible for this value to be greater than one, we expect T3 tests to be ordered less frequently relative to TSH.
• We also expect the T3/TSH ratio to be relatively lower than T4/TSH ratio.
FT3/T3 Shows the rate at which free T3 test is ordered relative to all T3-related testing (i.e., FT3, TT3)
• Unlike the case of FT4 versus TT4, there’s a lack of published guidelines that specifically recommends the use of FT3 or TT3.
• The use of FT3 and TT3 are clinical context-dependent.
rT3/TSH Shows the rate at which r T3 test is ordered relative to TSH
• The utility of rT3 in thyroid work-up is controversial, e.g., rT3 may be elevated in non-thyroidal illness.
• We expect the rT3/TSH ratio to be lower than T3/TSH and T4/TSH ratios.

Abbreviations: TSH = thyroid stimulating hormone; T4 = T4-related tests (i.e., free T4, total T4); T3 = T3-related tests (i.e., free T3, total T3); FT4 = free T4; TT4 = total T4; FT3 = free T3; TT3 = total T3; rT3 = reverse T3; T3U = T3 Uptake