This small tweak cuts T4 tests by one-third
One in three thyroid function follow-up tests could be avoided by using wider reference ranges before ordering free T4 testing, say endocrinologists.
After analysing thyroid function test results for 120,000 patients the WA researchers found that the upper TSH cut-off for ordering free T4 tests could be increased from 4mU/L to 6mU/L without missing cases of overt hypothyroidism.
Using a wider reference range of 0.2-6mU/L instead of the current 0.4-4mU/L range would miss 2.5% of patients with abnormal free T4 levels.
However, almost all of these patients were “healthy outliers”