It is a mistake to assume that clinical blood tests for thyroid function are infallible. In fact, it is my clinical experience (shared by other holistic doctors) that persons whose blood tests do not show problems often continue to have symptoms. When treated with either thyroid hormone or herbal alternatives, many of these patients improve dramatically. The simple tried and true method of taking the basal body temperature with a thermometer is often a more accurate way to assess thyroid status, and is certainly less expensive than laboratory evaluations. Blood tests measure the amount of thyroid hormone that is produced by the body and circulated in the blood, but they cannot tell if the body is utilizing the hormone properly at the cellular level.