Thyroid-Stimulating Hormone (TSH) is a hormone produced by the pituitary gland, a small gland located at the base of your brain. Its primary function is to regulate the thyroid gland, a butterfly-shaped organ in your neck. The thyroid gland, in turn, produces thyroid hormones, primarily thyroxine (T4) and triiodothyronine (T3), which control your body’s metabolism and influence various bodily functions, including heart rate, digestion, muscle control, and brain development. A TSH blood test is a common way to assess how well your thyroid is functioning.
Understanding TSH Levels
TSH acts like a messenger, signaling the thyroid gland to produce and release thyroid hormones. When levels of T3 and T4 in your bloodstream are low, the pituitary gland releases more TSH to stimulate the thyroid. Conversely, if T3 and T4 levels are high, the pituitary gland reduces TSH production to signal the thyroid to slow down. This feedback loop helps maintain a balanced metabolic rate.
Healthcare providers refer to a “normal reference range” for TSH levels, which falls between 0.4 and 4.0 milliunits per liter (mU/L) for most healthy, non-pregnant adults. Some studies suggest a narrower optimal range, such as 0.45 to 2.5 mIU/L. These ranges can vary slightly between different laboratories due to varying testing methods.
Interpreting a TSH Level of 1.39
A TSH level of 1.39 mIU/L falls within the normal reference range for most adults. This reading suggests that your thyroid gland is functioning well and producing appropriate amounts of thyroid hormones (T3 and T4). A level in this lower-mid range is considered optimal by many healthcare providers, particularly for individuals who are trying to conceive or are pregnant, where a TSH below 2.5 mIU/L is recommended.
This value signifies good thyroid health, but a healthcare professional will always consider a single TSH reading within the context of your overall health, any symptoms you might be experiencing, and potentially other thyroid hormone tests, such as free T4.
Factors Influencing TSH Results
Even with a TSH level within the normal range, various factors can influence the test result or its interpretation. TSH levels can fluctuate throughout the day, with levels higher in the morning. Certain medications can also affect TSH readings. For example, biotin supplements may interfere with test results, and some drugs like lithium, amiodarone, and certain antiepileptic medications can influence TSH levels.
Pregnancy alters TSH levels; they decrease in the first trimester before gradually rising later in pregnancy. Acute illnesses or hospitalizations, even those unrelated to the thyroid, can temporarily suppress TSH levels. Age is another factor, as normal TSH ranges can vary slightly, with some older individuals having slightly higher normal levels.
When to Consult a Doctor
While a TSH level of 1.39 mIU/L is considered normal, consulting a doctor is advisable in some situations. If you are experiencing symptoms associated with thyroid dysfunction, such as persistent fatigue, unexplained weight changes, mood swings, or changes in hair and skin, consult a doctor even with a normal TSH. These symptoms might suggest a different health issue or indicate that your “normal” TSH level isn’t optimal for your individual body.
Individuals with a family history of thyroid disease should discuss their TSH results and overall thyroid health with a healthcare provider. If you are pregnant or planning a pregnancy, close monitoring of thyroid function is recommended, as TSH targets can be more stringent during these periods. If you are taking medications known to affect thyroid function, or if your doctor has advised follow-up testing, it is important to comply with these recommendations. A single TSH reading is one piece of a larger health picture, and a doctor can provide a comprehensive assessment.