Thyroid Testing

27 September 2023

The thyroid sits at the base of the throat and incorporates iodine from the diet into the hormones which regulate your metabolic processes (metabolism). 

You’ve probably heard of metabolism – it’s the process that helps your body burn calories and affects your heart rate, blood pressure and body temperature. 

Anyone of any age can be affected by thyroid issues. 

Hypo (underactive) vs Hyper (overactive)

Because the thyroid is involved in many body processes, if it doesn’t function at normal capacity, you can become unwell.

If your doctor suspects a thyroid issue, they may send you for a TSH (Thyroid Stimulating Hormone) test to look for symptoms of either hypothyroidism (low levels of Thyroid Stimulating Hormone) or hyperthyroidism (high levels of Thyroid Stimulating Hormone).

These can appear as: 

Hypothyroidism

  • Fatigue
  • Weakness
  • Dry hair
  • Puffy face
  • Slow heart rate
  • Weight gain
  • Constipation
  • Irregular or heavy periods
  • Possible infertility and increased risk of miscarriage
  • Cold intolerance.

Hyperthyroidism

  • Hair loss
  • Fast heart rate
  • Weight loss
  • Diarrhoea
  • Bulging eyes
  • Infrequent menstrual periods with longer cycles
  • Nervousness
  • Sweating
  • Heat intolerance.

SA Pathology will test your blood sample for biomarkers of either condition.

Inside the lab

Once your sample arrives at the lab, the team will set up a screening test. The thyroid function test (TFT) is a very sensitive indicator of thyroid disease. This is because the pituitary gland detects small changes in circulating thyroid hormone levels and adjusts the TSH (thyroid stimulating hormone) accordingly.

However, there are a few situations where TSH may not be a good indicator of thyroid status, and then we also need to measure thyroid hormone levels.

If the clinical notes on the request form indicate previous abnormal results or known thyroid conditions, or if the TSH is outside the normal range, the laboratory will also perform free thyroxine (free T4) and sometimes free triiodothyronine (free T3) tests. 

These situations include:

  • Known or suspected pituitary disease.
  • Known thyroid disease- especially hyperthyroidism (overactive thyroid).
  • Absent periods not due to pregnancy, or infertility in either sex (as this may be due to pituitary or thyroid disease).
  • Dementia or psychiatric illness (as this may be due to thyroid disease).

Sometimes TSH and/or thyroid hormone levels are so unusual that the team will phone the requesting doctor; this is particularly the case for children and pregnant women, as thyroid hormone is essential for a growing child’s brain development. 

If thyroid function tests are very abnormal, the results are also reviewed by a pathologist, who may also contact the requesting clinician to discuss.

If you’ve spoken to your doctor and are ready to review your TSH levels, head to an SA Pathology collection centre near you.  

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