Basic thyroid test panel (TSH, FT3, FT4)

Description

What this panel is for

Three tests from a single sample: TSH (the pituitary hormone that controls the thyroid), FT4 (free thyroxine, the main thyroid hormone) and FT3 (free triiodothyronine). TSH alone shows whether the thyroid is underactive or overactive; FT4 and FT3 show to what extent. TSH responds first and is the most sensitive indicator: it rises when the thyroid is underactive and falls when it is overactive. FT4 shows whether the disorder is overt or still subclinical. FT3 is most often requested alongside TSH because the relationship between these hormones helps assess thyroid function; in hyperthyroidism, the doctor adds it to TSH and FT4.

When to consider this test

• tiredness, weight gain, feeling cold, dry skin, constipation or low mood (suspected hypothyroidism),
• weight loss, palpitations, hand tremor, nervousness, insomnia or diarrhoea (suspected hyperthyroidism),
• monitoring treatment with levothyroxine or antithyroid medicines,
• abnormal TSH on screening,
• planning a pregnancy, menstrual irregularities or infertility,
• a family history of thyroid disease, or treatment with amiodarone, lithium or interferon.

How to prepare

• Attend in the morning after fasting for 8–12 hours, drinking only water; TSH follows a daily rhythm and may be lower in the afternoon.
• Take levothyroxine (Euthyrox, Letrox) after sample collection.
• Stop high-dose biotin for 2–3 days; it may distort TSH, FT4 and FT3 results obtained using immunoassays.
• Avoid testing during an acute infection or in the first few weeks after a serious illness; results may be temporarily abnormal.

Understanding your result

TSH is reported in mIU/l (approximately 0.3–4.2 mIU/l in adults according to Mayo Clinic Laboratories; doctors use lower thresholds in pregnancy), and FT4 and FT3 in pmol/l or ng/dl. Compare your result with the reference range on the report.

A single abnormal TSH result returns to normal spontaneously in a substantial proportion of people, so the doctor usually repeats the test before starting treatment. The result is interpreted alongside symptoms and ultrasound findings.

Other tests to consider

For abnormal TSH or a family history of Hashimoto’s thyroiditis: anti-TPO, anti-TG; for hyperthyroidism, TRAb. All five thyroid tests in one panel: thyroid test panel+ (TSH, FT4, FT3, anti-TPO, anti-TG); TSH and FT4 alone: thyroid test panel (TSH, FT4). Read more: an article on hypothyroidism at Badania-Medyczne.pl.

Sources: ALAB laboratoria, Thyroid panel (preparation, levothyroxine after sample collection, biotin, TSH/FT4 interpretation); ALAB laboratoria, TSH, FT3, FT4, anti-TG, anti-TPO panel (interpretation guide); Mayo Clinic Laboratories, Thyroid-Stimulating Hormone-Sensitive, Serum (TSH reference ranges by age, subclinical hypothyroidism and hyperthyroidism). For information only; does not replace medical advice.