Home Biomarkers TSH

TSH

Thyroid Biomarker

Sample Needed

Collection Type: Blood

Body System

Related System: Thyroid

Overview

Thyroid-stimulating hormone (TSH) is a pituitary-produced hormone that regulates the thyroid gland’s production of thyroxine (T4) and triiodothyronine (T3). A TSH blood test measures circulating TSH to assess whether the thyroid is underactive (hypothyroidism) or overactive (hyperthyroidism), or whether pituitary dysfunction is present. It is commonly used to investigate symptoms such as fatigue, weight change, heat/cold intolerance, palpitations, menstrual irregularities or hair loss. Women and older adults are more likely to develop thyroid disease; pregnancy and age can alter target ranges (early pregnancy often lowers TSH), and some medications or acute illness can transiently change results.

People also test for

Test Preparation

Sample to be given at the same time of the day in follow-up cases
Do not stop taking your thyroid medications on the day of the test unless otherwise advised by the doctor

Why Do I Need This Test

Profile: Included in the Thyroid profile (often with free T4 ± free T3, antibodies).
Symptoms: Fatigue, weight gain/loss, temperature sensitivity, palpitations, mood or menstrual changes.
Diagnoses/monitoring: Primary hypothyroidism, hyperthyroidism, subclinical disease, monitoring replacement or suppression therapy.
Causes of abnormal levels: autoimmune disease (Hashimoto’s, Graves’), thyroiditis, pituitary disease, medications, iodine excess/deficiency.
Biological meaning: High TSH usually means underactive thyroid; low TSH usually means overactive thyroid or central pituitary problem.
Behaviors/lifestyle/family history: iodine intake, smoking, certain drugs (amiodarone, lithium), and family history of thyroid disease increase likelihood of testing.

Run our symptom checker to see if this test is right for you

Symptom Checker

Understanding Test Results

TSH <0.1 mIU/L: Strongly suggests overt hyperthyroidism (especially if free T4/T3 are high); urgent evaluation and treatment often needed if symptomatic.
TSH 0.1–0.4 mIU/L: May indicate subclinical hyperthyroidism—risk for atrial fibrillation and bone loss if persistent.
TSH 0.4–4.0 mIU/L: Considered normal for most adults; interpret with free T4 and clinical context (pregnancy and elderly may use adjusted ranges).
TSH 4.0–10 mIU/L: Suggests subclinical or mild primary hypothyroidism; monitor and evaluate for symptoms and antibodies.
TSH >10 mIU/L: Consistent with overt primary hypothyroidism—high likelihood of needing levothyroxine.
Note: Low/normal TSH with low free T4 may indicate central (pituitary/hypothalamic) hypothyroidism.
Medications, recent illness, pregnancy, and transient thyroiditis can alter TSH—repeat testing and correlate with clinical picture.

Normal Range

0.4-4.0 mIU/L

FAQs

Q: What happens when TSH is high?

A: When TSH is high it usually means the pituitary is signalling an underactive thyroid (hypothyroidism). Low thyroid hormone causes fatigue, weight gain, cold intolerance, constipation, dry skin, hair loss, slowed heart rate and depressed mood. Persistent high TSH can raise cholesterol, cause goitre, infertility and cardiovascular risk. Diagnosis uses TSH plus free T4 and antibody tests; treatment is usually levothyroxine replacement.

Q: What is TSH for females?

A: Thyroid‑stimulating hormone (TSH) is produced by the pituitary to regulate thyroid hormone production. For adult females, the usual reference range is about 0.4–4.0 mIU/L, with lower targets in pregnancy (first trimester often <2.5 mIU/L). High TSH suggests an underactive thyroid (hypothyroidism); low TSH suggests an overactive thyroid (hyperthyroidism). Abnormal results need clinical evaluation.

Q: How to reduce TSH?

A: Lower elevated TSH by treating hypothyroidism with prescribed levothyroxine and adjusting dose under medical supervision. Take it consistently on an empty stomach and avoid calcium, iron, antacids or soy within four hours of dosing. Monitor TSH regularly, review interacting medications, and consult an endocrinologist if levels remain high. Address possible iodine imbalance and ensure adherence; lifestyle measures support but don’t replace therapy.

Q: What happens when TSH is low?

A: When TSH is low, it usually signals excess thyroid hormone (hyperthyroidism) or too much thyroid replacement. Symptoms include weight loss, palpitations, anxiety, heat intolerance, tremor, and insomnia. Long-term effects may include atrial fibrillation and decreased bone density. Rarely, low TSH reflects pituitary (central) dysfunction. Doctors check free T4/T3, find the cause, and treat to normalize levels.

Q: Is high TSH life threatening?

A: A high TSH usually indicates underactive thyroid (hypothyroidism). Mild or subclinical elevations are rarely immediately life‑threatening and are treated with monitoring or replacement. However, severe, untreated hypothyroidism can progress to myxedema coma a rare, life‑threatening emergency and increases cardiovascular risk. See your clinician for evaluation, treatment, and urgent care if severe symptoms occur.

Q: Can stress cause high TSH levels?

A: Stress can influence the hypothalamic–pituitary–thyroid axis: acute stress often lowers TSH, while chronic stress and high cortisol may alter thyroid hormone conversion and feedback, potentially affecting TSH. Stress can unmask or worsen underlying hypothyroidism or autoimmune thyroid disease, but it is usually not the sole cause of a persistently high TSH—medical evaluation and repeat testing are advised.