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Fact Sheet 3 – Improvements in Diagnosis and Treatment: TSH Assay Test

The routine blood tests for thyroid function are extremely accurate and precise. The blood tests for thyroid stimulating hormone (TSH, which is the pituitary hormone that stimulates the thyroid even more when it is failing) is extremely accurate. It is the first to rise when thyroid function is at all low. Indeed it will go up even before the thyroid hormones are detectably lower and an individual can be clearly diagnosed as being hypothyroid or as having borderline or compensated hypothyroidism. It is important to remember that many other conditions can mimic the symptoms of hypothyroidism, most particularly, chronic anxiety, depression and stress. In these cases the TSH will not fluctuate. The sensitive TSH test will also indicate the presence of hyperthyroidism if the TSH is below normal.

The normal range for TSH depends on the type of assay used. Currently with the sensitive assays now available, the usual normal range is between 0.3 and 3.5 milliunits/L. Assays vary a little from laboratory to laboratory.

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