TFTs

Hypothyroidism

  • Overt primary hypothyroidism (T4 low, TSH raised > 10)
    • Start levothyroxine (if transient thyroiditis is excluded)
  • Subclinical primary hypothyroidism (T4 normal, TSH raised)
    • Many cases are transient
    • TSH < 10
      • repeat after 3 months to see if changes are persistent/progressive
      • request anti-TPO antibodies to determine if autoimmune process and help predict risk of progression to overt hypothyroidism
      • On repeat test
        • TSH > 10 mU/L
          • start levothyroxine
        • TSH 4.5 – 10 mU/L
          • annual monitoring
          • a trial of T4 can be considered if symptomatic with goitre or planning pregnancy or anti-TPO positive
  • Levothyroxine (T4 replacement)
    • Initiation
      • start at 50 mcg OD then increase in 25mcg increments
        • monitor TFTs after 8 weeks and titrate accordingly
      • if older or IHD, consider starting at 25mcg OD
      • Aim for TSH and free T4 within normal range and patient to feel well
    • When to refer
      • TSH not in normal range despite Levothyroxine 200mcg OD
      • Symptoms despite adequate TFTs
      • < 16 years old
      • Pregnant or postpartum
      • Nodular goitre
    • Interactions
      • OTC medications that impair T4 absorption – PPIs, H2 antagonists, calcium carbonate, ferrous sulphate, soy protein, aluminium hydroxide
      • Higher T4 requirement may be required in patients who are pregnant, on anticonvulsants or oestrogen containing oral contraceptives
      • Do not take T4 within 4 hours of taking other medications
  • T3 replacement
    • Rarely required, no consistent evidence of its use combined with T4
    • Aim of T3 therapy is to normalise TSH
    • T3 measurements are of limited value due to variability of T3 concentrations of blood after T3 dose
    • Measurement of free T4 is of no value in assessing patients on T3
  • Hypopituitarism
    • Diagnosis
      • Secondary hypothyroidism should be considered in patients present with low T4 and low/normal/slightly raised TSH
      • However most low T4, normal TSH is due to non thyroid illness or use of medications such as NSAIDs, furosemide, anti-convulsants or high dose glucocorticoids

 

Hyperthyroidism

  • Over hyperthyroidism TSH < 0.01 mU/L, Free T4/T3 high
    • Refer to endocrinology
  • Subclinical hyperthyroidism TSH < 0.01 mU/L, Free T4/T3 normal
    • Exclude illness and drugs (dopaminergic drugs, high dose steroids) that suppress TSH
    • Repeat TSH/FT4/T3 1 month later
      • If abnormalities persist – refer to endocrinologist
      • If improvement, monitor every 6-12 months