KISS: Subclinical Hypothyroidism (SCH) in Adults

BMJ2019;365;l2006  JAMA2018;320;1349  NICE NG 145

Background:

• Definition: a raised TSH but normal free thyroxine levels. 
• Occurs in up to 20% of the population & in many cases is transient.
• TSH levels vary with stress, transient disease and age with TSH increases in older adults normally.
• 2%-5% progress to overt hypothyroidism annually (more likely if thyroid peroxidase (TPO) antibodies are positive, or in those with higher TSH levels >20mIU/L).

Management: 

• Confirm SCH in adults <65: Repeat TSH, FT4 and check TPO antibodies in 3 months.
• Check if the person is taking biotin supplements - this can give falsely high, or low blood thyroid readings. 
• NICE recommends the following:
  • Consider levothyroxine for adults with SCH and TSH ≥ 10mIU/L.
  • Consider a 6-month trial of levothyroxine for adults < 65 years old with SCH and TSH < 10mIU/L AND symptoms of hypothyroidism BUT if symptoms persist when TSH normalises consider stopping the levothyroxine.
  • When considering treatment take into account factors associated with an increased risk of progressing to overt hypothyroidism i.e. raised TPO antibodies, previous thyroid surgery or radioactive iodine.
• However, be aware that based on new research JAMA2018;320;1349, there is a new STRONG guideline recommendation BMJ2019;365;l2006 NOT to offer thyroxine treatment to adults with SCH even if they are symptomatic - evidence most strong for adults >65: 
  
  • This recommendation does NOT apply to the following groups: Pregnancy, planning pregnancy or risk of unplanned pregnancy (see separate chapter Thyroid, pregnancy and fertility), patients with very severe symptoms, a TSH > 20mIU/L or young adults aged under 30.

Monitoring: 

• NICE recommends the following:
  • Measure TSH/FT4 yearly if raised TPO antibodies or previous thyroid surgery/radioactive iodine.
  • Measure TSH/FT4 every 2-3 years for all other adults.
• However, be aware NIHR recommendation that in healthy adults aged over 65, repeat thyroid testing is not needed unless patients have risk factors for, or develop signs or symptoms of overt hypothyroidism BMJ2019;364;1804