Hypothyroidism is a metabolic disorder. It disrupts the levels of thyroid hormones that regulate metabolism. Both primary and secondary hypothyroidism qualify as metabolic disorders because the thyroid's hormonal output directly controls how your body converts food into energy.
Blood tests that diagnose and monitor hypothyroidism
| Test | Normal Range | In Hypothyroidism | What It Tells You |
|---|---|---|---|
| TSH | 0.4–4.0 mIU/L | Elevated (>4.0 mIU/L) | First-line; high TSH = pituitary signaling thyroid to work harder = underactive thyroid |
| Free T4 | 0.8–1.8 ng/dL | Low (<0.8 ng/dL) | Confirms low hormone production; used alongside TSH to stage severity |
| Free T3 | 2.3–4.2 pg/mL | Low-normal or low | Active hormone; more useful in T3-deficiency states and monitoring |
| Anti-TPO antibodies | <35 IU/mL | Elevated in Hashimoto's | Identifies autoimmune cause (Hashimoto's thyroiditis = most common hypothyroidism cause) |
The link between thyroid hormones and metabolic processes is complex. People with hypothyroidism often present with many nonspecific symptoms. For more information on our Thyroid Panel test, or to book an appointment, visit the links.
What is a metabolic disorder?
Metabolism is the system of chemical reactions your body uses to convert food into energy. Any organ that plays a role in metabolism can become impaired, leading to a metabolic disorder.
Type 2 diabetes is a common example — it results from impaired pancreatic function. Similarly, hypothyroidism is a metabolic disorder that arises from impaired thyroid function. Both slow the body's ability to regulate energy normally.
What is hypothyroidism?
The thyroid hormones triiodothyronine (T3) and thyroxine (T4) control many physiological processes, including metabolism. When the thyroid produces insufficient amounts of these hormones, those processes slow or stop. This is hypothyroidism.
Signs and symptoms of hypothyroidism
Hypothyroidism often presents with multiple nonspecific symptoms. When several appear together, a physician may suspect hypothyroidism as the underlying cause.
- Unexplained weight gain or fluid retention
- Feeling colder than normal
- Tingling or numbness in the feet and hands
- Depression or mood swings
- Hair loss or dry hair
- Inability to sweat
- Coarse skin or puffy face
- Constipation
- Abnormal menstrual bleeding
- Slow heart rate or enlarged heart
- Slow speech
Types of hypothyroidism and their causes
Hypothyroidism has two presentations: primary and secondary. Primary hypothyroidism comes from thyroid disease. Secondary hypothyroidism results from disease in the pituitary gland or hypothalamus.
Primary hypothyroidism most commonly results from Hashimoto's thyroiditis, an autoimmune disorder. Less often, treatments for hyperthyroidism — such as radioactive iodine therapy — can trigger it. Several medications can also cause primary hypothyroidism:
- Lithium, amiodarone, interferon-alfa
- Checkpoint inhibitors, tyrosine kinase inhibitors
- Propylthiouracil, methimazole, imatinib
- Carbamazepine, phenytoin, prednisone
- Drugs containing iodine
Secondary hypothyroidism occurs when the hypothalamus fails to produce enough TRH. Without TRH, the pituitary cannot produce enough thyroid-stimulating hormone. The resulting imbalance reduces T3 and T4 production.
How to treat hypothyroidism
Hypothyroidism is manageable with the right treatment. Levothyroxine (Synthroid) is the first-line medication. Dosing is based on the patient's weight and hormone levels. The goal is to restore T3 and T4 to normal ranges.
Your doctor will re-evaluate hormone levels 1–2 months after starting therapy to check your response and adjust the dose. Levothyroxine can manage thyroid levels long-term with regular monitoring. Left untreated, hypothyroidism can increase the risk of heart failure. Severe untreated cases can lead to myxedema coma.
Talk to your doctor if you experience side effects from levothyroxine, including heat intolerance, muscle weakness, chronic headaches, sleep problems, weight loss, or skin rashes.
Test your thyroid with Speedy Sticks
Speedy Sticks is a mobile concierge phlebotomy service. We provide at-home blood draws and on-site diagnostic screenings for individuals and businesses. To test your thyroid, book an appointment and select our thyroid panel test.
Thyroid blood tests can be collected at home through mobile phlebotomy — no clinic trip needed for TSH, free T4, and antibody panels.
Sources and further reading
Thyroid Panel at Home
TSH, free T4, free T3, and Anti-TPO antibodies — all drawn at home in one visit. A certified phlebotomist comes to your door on your schedule.
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