Bilan thyroïdien : guide complet TSH, T3 et T4

The thyroid gland produces hormones that regulate metabolism, energy, body temperature, heart rate, and virtually every organ system. Understanding each test is essential:

• TSH (Thyroid Stimulating Hormone): Produced by the pituitary gland. Acts as the "thermostat" — when thyroid hormones are low, TSH rises to stimulate the thyroid. When thyroid hormones are high, TSH decreases. Normal range: 0.4-4.0 mIU/L. TSH moves inversely to thyroid function.
• Free T4 (Thyroxine): The primary hormone produced by the thyroid gland. "Free" means not bound to protein and therefore active. Normal range: 0.8-1.8 ng/dL. T4 is the storage form that converts to active T3.
• Free T3 (Triiodothyronine): The active thyroid hormone (3-5x more potent than T4). Most T3 is produced by conversion from T4 in the liver and kidneys. Normal range: 2.3-4.2 pg/mL.
• Thyroid antibodies: Anti-TPO (thyroid peroxidase) and anti-Tg (thyroglobulin) antibodies indicate autoimmune thyroid disease (Hashimoto's or Graves' disease). Present in 90% of Hashimoto's patients.

Upload your thyroid panel results to WAYJET's Medical Report Analyzer for a comprehensive interpretation including optimal ranges and pattern analysis.

Thyroid dysfunction patterns can be identified by the relationship between TSH and thyroid hormone levels:

• Primary hypothyroidism (underactive): High TSH + Low free T4. Most common cause: Hashimoto's thyroiditis (autoimmune). Symptoms: fatigue, weight gain, cold intolerance, constipation, dry skin, hair loss, depression.
• Subclinical hypothyroidism: Mildly elevated TSH (4.0-10.0) + Normal free T4. Affects 4-8% of adults. Treatment is debated — many endocrinologists treat when TSH exceeds 10 or when symptoms are present.
• Hyperthyroidism (overactive): Low/suppressed TSH + High free T4/T3. Most common cause: Graves' disease (autoimmune). Symptoms: weight loss, rapid heartbeat, anxiety, tremor, heat intolerance, sweating.
• Central hypothyroidism (rare): Low/normal TSH + Low free T4. Indicates pituitary problem rather than thyroid disease.
• Sick euthyroid syndrome: Low T3 + Normal/low T4 + Normal/low TSH during severe illness. Not true thyroid disease — resolves when the acute illness resolves.

The "optimal" TSH debate: while the standard normal range is 0.4-4.0, many functional medicine practitioners target 1.0-2.5 mIU/L for optimal well-being. The upper limit of normal has been debated since a 2002 NHANES study suggested 95% of disease-free individuals have TSH below 2.5.

Thyroid dysfunction is common but frequently underdiagnosed. Consider testing if you experience:

• Hypothyroid symptoms: Unexplained fatigue, weight gain despite no dietary changes, feeling cold constantly, constipation, brain fog, depression, dry skin, hair loss, menstrual irregularities, elevated cholesterol
• Hyperthyroid symptoms: Unexplained weight loss, rapid heartbeat, anxiety, tremor, excessive sweating, diarrhea, insomnia, menstrual changes

Populations that should be routinely screened:

• Women over 35 (every 5 years per American Thyroid Association)
• Pregnant women or those planning pregnancy (thyroid dysfunction affects 2-3% of pregnancies)
• People with type 1 diabetes or other autoimmune conditions
• Those with family history of thyroid disease
• Post-radiation patients (head/neck area)
• Patients on medications affecting thyroid: amiodarone, lithium, immunotherapy

Important: request a complete thyroid panel (TSH + free T4 + free T3 + TPO antibodies), not just TSH alone. TSH alone can miss subclinical dysfunction and does not reveal conversion issues (normal T4 but low T3). Many standard checkups only include TSH.