#249 Helping physicians fatigued by TSH Screening and Subclinical Hypothyroidism
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- Clinical endpoints: Four systematic reviews (with 18-21 RCTs)1-4 from the last 5 years report on 18-21 RCTs.1-4 Treatment of subclinical hypothyroidism (levothyroxine typically) versus placebo had no effect on:
- Mortality or new cardiovascular disease.2-4
- Quality of life, depressive symptoms, fatigue, or thyroid-related symptoms scores.1-4
- Cognitive function.1-4
- Newest RCT, 251 elderly patients (mean age 85), no benefit on any outcome (~1.5-year follow-up).5
- Surrogate markers:
- Blood Pressure (BP): Three systematic reviews found no difference,1,2,4 while another found systolic BP reduced 2.5 mmHg (not diastolic).6
- Lipids: Of four systematic reviews, two found no effect and two found treatment reduced total cholesterol or LDL 0.1-0.6 mmol/L (no change in HDL or triglycerides).7,8
- There is no evidence these small, inconsistent changes matter clinically.
- Subclinical Hypothyroidism generally defined as TSH ~4-10mIU/L, with normal T3/T4 and no clear symptoms of hypothyroidism.
- TSH may vary up to 50% between tests9 and daily fluctuations10 in individuals can be 26%.
- Prevalence of subclinical hypothyroidism (in the developed world) is 4-10%, with 2-6% of these developing overt hypothyroidism. Subclinical hyperthyroidism prevalence is ~2% with 1-2% of these developing overt hyperthyroidism.2,11
- 40% subclinical hypothyroidism revert to normal over ~2.5 years.12
- Symptoms are often poor predictors. Example: one study found ~18% of euthyroid, ~22% subclinical hypothyroid, ~26% overt hypothyroid patients reported ≥4 symptoms of hypothyroidism.13
- Canadian Task Force on Preventive Health Care recommends against screening for thyroid function in asymptomatic non-pregnant patients or treating subclinical hypothyroidism.14