When a thyroid test could be wrong
Because many patients have thyroid problems with no symptoms, most doctors rely on lab tests of all three hormones to confirm a diagnosis of thyroid disease. The problem is that these tests will show accurate levels of thyroid hormone in the blood, but not how much the body is able to use, or how much is necessary inside each cell of the body for an individual patient's health.
The reference values, based on a cross section of so called "normal" thyroid function, are very loose; many people who register as normal may need higher levels of hormone to function efficiently, and others register as underactive even though this lower output is adequate for their needs. Thyroid tests also have a high degree of inaccuracy.That's why it's vital that you undergo several tests and even repeat the same test at a different laboratory.
If the results of your T3 and T4 hormone test are inconclusive, you should have a TSH test. (But opt for the highly sensitive chemoluminescent or immunoradiometric tests, or it won't give a true reading; standard TSH tests is not reliable when you have a low TSH level.) A more accurate indicator may be the Basal Body Temperature test (see p 3) .
If you have a nodular goitre (a swelling with extra nodes) you might need an ultrasound scan to exclude cancer. A radionucleotide thyroid scan will only tell you which parts of the thyroid are functioning properly and which aren't.
In certain conditions, thyroxine (T4) readings can be thrown off. These include:
While taking the Pill
After crash dieting
After a long standing weakness, such as ME
In certain types of kidney patients
When treated with androgens or steroids
When taking phenytoin or carbamazepine.
One useful blood test looks for autoimmune diseases. This will determine if your body is producing antibodies that are attacking its own thyroid cells and identify problems like Graves' or Hashimoto's disease.