was macht l thyroxin im körper — which blood markers matter?

L-thyroxine (levothyroxine) is synthetic thyroxine (T4), used to treat hypothyroidism or after thyroid removal. It is converted in the body to active triiodothyronine (T3). Proper dosing is critical: too little causes hypothyroid symptoms, too much can lead to hyperthyroidism and cardiac risks. Key blood markers for monitoring are: TSH (most sensitive), free T4 (fT4), and sometimes free T3 (fT3). In autoimmune thyroiditis (Hashimoto), antibodies (TPO-Ab, Tg-Ab) help confirm the cause. Evidence for these markers is human-strong, supported by decades of clinical guidelines. In the provided context, MyBody-X does not offer a thyroid test; their blood tests cover iron (ferritin) and cortisol, which are not directly relevant for thyroxine management. Caveat: Never adjust thyroxine dose without medical supervision. Blood should be drawn fasting and before taking the morning tablet. A full thyroid panel requires a doctor's order, not a direct-to-consumer test.