What is the best lab test to see if thyroid problems are causing hair loss?

Are thyroid problems causing hair loss?

Thyroid hormones are produced by the  thyroid gland, which is a small gland located in the midline of the neck. Precise levels of thyroid hormones are important for normal hair growth. 

The TSH test

The release of thyroid hormones from the thyroid gland is an intricate process. A region of the brain known as the hypothalamus releases a hormone known as "TRH" or thyrotropin releasing hormone, which in turn triggers the tiny pituitary gland to release "TSH" or thyroid stimulating hormone.  In response to the release of TSH, the thyroid gland produces thyroid hormones, namely thyroxine (T4) and triiodothyronine (T3).

When the body produces too much or too little thyroid hormone this may lead to hair shedding. The single best test for thyroid problems is a blood test for “TSH” or thyroid stimulating hormone.  If the TSH is abnormal, several additional thyroid tests can be ordered, including a "free T4".

Hypothyroidism occurs in about 3 % of the population. Hypothyroidism occurs when the thyroid gland does not release enough thyroid hormone. Most patients who are hypothyroid have an abnormally high TSH level and a low free T4 level. This is known as "primary hypothyroidism"  Most patients who are hyperthyroid have the opposite pattern – a low TSH level and high free T4 levels.