Many of the systems can be affected by poor thyroid function. This means hypothyroid can be difficult to detect, your GP may consider many different possibilities before considering testing for thyroid function.
Regular thyroid function tests are notoriously inaccurate when detecting hypothyroid. They really only give a snapshot of what is happening at any one point. It also only tells us what is happening in the bloodstream, not information about cellular uptake.
I often use clinical symptoms to guide me towards the possibility of thyroid dysfunction along with checking the basal metabolic rate of an individual by using information from a morning temperature test.
This list is not exhaustive but these are the more common signs of thyroid dysfunction.
low body temperature
unexplained fluid retention
loss of sex drive
infertility or recurrent miscarriage
Your local Nutrition Practitioner can arrange a urine test to uncover possible hypothyroid issues.