Thyroid Essentials

• TSH: the signal your pituitary sends to the thyroid. It usually rises when thyroid hormone is low and falls when thyroid hormone is high.
• Free T4: the main hormone the thyroid releases, measured in its unbound, available form.
• Free T3: the more active hormone, made mostly by converting T4 in tissues outside the thyroid.
• Reverse T3: an inactive form made from T4. Levels can rise during illness, calorie restriction and with some medications.
• TPO and thyroglobulin antibodies: markers of thyroid autoimmunity. Most people with Hashimoto's have TPO antibodies, and thyroglobulin antibodies are found in many.

This panel suits people with hypothyroidism or Hashimoto's who want to follow their thyroid function over time, and people with symptoms or a family history of thyroid disease who want more than a TSH-only check.

If you are pregnant or recently unwell, thyroid results read differently. Talk with your clinician about timing.

Consider testing when symptoms appear or change, or as a baseline if thyroid disease runs in your family. After starting or changing a thyroid medication dose, TSH generally takes about 6 to 8 weeks to settle, so testing sooner can mislead.

For results you can compare over time, test at a similar time of day, because TSH varies through the day.

No fasting is needed.

• Thyroid medication: if you take levothyroxine or another thyroid medication, have your blood drawn before that day's dose and bring the dose with you. Keep taking your medication as prescribed otherwise.
• Biotin: high-dose biotin, common in hair, skin and nail supplements, can distort many of these lab results. Stop it at least 2 to 3 days before your draw.

Your report shows Quest's reference range next to each result. These patterns are the ones clinicians commonly look for:

• High TSH with low Free T4: the typical pattern of an underactive thyroid.
• High TSH with normal Free T4: the pattern called subclinical hypothyroidism.
• Low TSH with high Free T4 or Free T3: the typical pattern of an overactive thyroid.
• Positive antibodies with normal hormone levels: thyroid autoimmunity is present, while thyroid function is currently normal. Antibody levels do not track how you feel.

If you take thyroid medication, your clinician sets your TSH goal. Recent illness, pregnancy and some medications can shift these results, and one result is best confirmed before any change in care.