TSH comes from the pituitary and tells the thyroid how hard to work. When thyroid hormone is low, TSH usually rises. When thyroid hormone is high, TSH usually falls. T4 is the main hormone released, and T3 is the more active form.
A single mildly high TSH with normal T3 and T4 is common and is not an emergency. Repeat testing, symptoms and antibodies decide whether treatment starts. A very low TSH with a racing heart, weight loss or tremor should be discussed promptly.
Reference ranges differ slightly by lab method. Compare a new report with an older one from a similar assay if you can. Bioline's counselling call walks through the flags. It does not start or stop medicine.
This article explains how tests are used. It is not a personal diagnosis.