Updated Thyroid Test Result Comments

April 2024
Ampath | ampath.co.za

Overview

Ampath has revised the interpretive comments provided on thyroid function test results, in line with the latest SEMDSA/ACE and international guidelines. The updates also include children and neonates, and integrate thyroid antibody results into comments for:

• Primary overt hypothyroidism
• Subclinical hypothyroidism
• Primary hyperthyroidism

1. Subclinical Hypothyroidism Updates

• TSH >10.0 mIU/L with normal FT4 and FT3:
  • Treatment is recommended due to increased risk of coronary heart disease (CHD).
• TSH persistently elevated but <10.0 mIU/L:
  • Treatment decisions should be based on clinical judgement, especially in the presence of:
    • Goitre
    • Cardiovascular disease (CVD) or risk factors
    • Type 2 diabetes
    • Dyslipidaemia
    • Psychiatric illness
    • Hypothyroid symptoms
  • Antibody status matters:
    • Increased anti-TPO or anti-TG antibodies → ~4.3% yearly risk of progression to overt hypothyroidism
    • If antibodies are not elevated → ~2.6% risk per year
    • If untreated, annual TSH testing is advised
• TSH increases with age:
  • In patients >65 years, TSH values up to 6.0 mIU/L may be normal if FT4 and FT3 are normal
  • May even provide a physiological advantage

2. Thyroid Antibodies – Clinical Relevance

• Anti-TPO or anti-TG antibodies:
  • Seen in up to 95% of Hashimoto’s disease cases during active phase
  • Levels do not correlate with disease severity
• Graves’ disease:
  • Associated with TSH receptor antibodies (TSHRAb)
  • May also show elevated anti-TPO or anti-TG in up to 80% of cases
• Other autoimmune diseases:
  • Elevated thyroid antibodies also observed in:
    • Pernicious anaemia
    • Rheumatoid arthritis
    • Type 1 diabetes
    • Addison’s disease
    • Coeliac disease
  • Present in up to 40% of patients with these conditions
• Healthy population:
  • Elevated antibodies found in 5–10% of individuals without thyroid disease
• Interpretation tip:
  • Elevated antibodies with normal thyroid function suggest a higher risk for developing future thyroid disease, especially hypothyroidism

3. Thyroid Hormone Treatment Targets

• Accurate comments depend on providing thyroid hormone therapy information on the request form.
• Updated targets:
  • In patients >65 years, TSH target is now 4.0–6.0 mIU/L
• Monitoring notes:
  • In athyreotic patients on Eltroxin, FT3 may be low or low-normal—clinical relevance is uncertain
  • In patients on Tertroxin, FT4 is expected to be low, and should not be used as a treatment target

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