TSH

TSH levels rise when the thyroid is underactive (hypothyroidism) and fall when it is overactive (hyperthyroidism). Both conditions can affect energy, metabolism, weight, mood, and heart function. Monitoring TSH helps detect thyroid imbalance early, often before symptoms become obvious, allowing timely treatment to maintain stable metabolism and overall health.

Most adults benefit from checking TSH once a year. If you're on thyroid medication, retest 6 to 8 weeks after any dose change. Once stable on a dose, annual checks are enough.

At baseline / for screening: Once every 12 months from age 30. More frequently if you have a family history of thyroid disease, are pregnant or planning pregnancy, have an autoimmune condition, or notice symptoms suggesting thyroid dysfunction (energy, weight, mood, temperature regulation).

When monitoring an intervention or change: Retest 6 to 8 weeks after starting or adjusting thyroid medication (levothyroxine, liothyronine, antithyroid drugs), since that's how long TSH takes to reach a new steady state. Acute illness and severe caloric restriction can shift free T3 downward independent of thyroid function, so wait for those to resolve before reading the trend.

Note: Biotin supplements above 5 mg per day interfere with the TSH assay, so pause biotin for 48 to 72 hours before testing. In pregnancy, retest TSH every 4 to 6 weeks; after severe non-thyroidal illness, wait 4 to 6 weeks for recovery before reading TSH as a stable value.