Endocrine Abstracts

Introduction: There continues to be much discussion around optimization of thyroid hormone status in hypothyroid individuals. We looked the way that FT4/TSH relate to each other in people who underwent a check of thyroid function (TFT) split between those on levothyroxine replacement (monitoring-test) and those who underwent TFT check as a screening test for thyroid hormone imbalance not-on-levothyroxine.

Methods: TFT test (FT4/TSH) results were taken from the Salford Hospital (UK) laboratory system for a 3-year period. To minimise comorbidity effects only samples taken in GP-Practices were used and for untreated patients only those who had single tests results were used. For treated patients, median value across all results was used.

Results: Total data included 290,000 tests for 130,000 patients. However, the FT4/TSH results were used from 12,006 (F 9,231/M 2,775 & (age <60 5,850 & age >=60 6,567)) treated patients with 43,846 actual test results. These were compared to the single results for 43,394 untreated patients (F 24,386/M19,008 & Age<60 32,537/Age>=60 10,857). Cluster analysis showed overall for untreated patients, median values for TSH=1.8 mUnits/l and FT4 =15.5 pmol/l, with 24% patients falling outside the 5%/95% limit, while for treated patients median TSH=3.6mUnits/l (+100% vs untreated) and FT4=18.9 pmol/l (+22%), with 22 % of treated patients falling outside the treated 5%/95% percentile boundary. When considered against the untreated boundary, 75% of treated results fell outside; by sex females 78%, males 68%; by age <60 73%, >=60 74%.

Conclusion: The current treatment regimens being applied of either low or high dose levothyroxine are not delivering the expected laboratory TFT profiles, with significant numbers of treated individuals being well outside expected values - both TSH/FT4 being significantly higher. This effect seems to be more prevalent in women than men - more concerning given the higher number of women requiring thyroid-hormone replacement.