Thyroid
Not for thyroid nodules, thyroid cancer or congenital hypothyroidism.
Screening
- CTFPHC Canadian Task Force on Preventive Health Care
- CWC Choosing Wisely Canada
- INESSS Institut national d'excellence en santé et services sociaux
| Decision | Guideline |
|---|---|
| Asymptomatic adults | Do not screen for thyroid dysfunction in non-pregnant adults 18 and older in primary care (strong recommendation, low-certainty evidence). CTFPHC 2019 opens in a new tabChoosing Wisely Canada, family medicine opens in a new tabINESSS 2026 opens in a new tab |
| Not covered by this advice | Pregnancy, or any of these:Previously diagnosed thyroid disease or thyroid surgery Thyroid medication, or drugs that may affect thyroid function (lithium, amiodarone) Previous or ongoing radioiodine therapy, or head and neck radiotherapy Pituitary or hypothalamic disease |
| Test when warranted | Stay alert to risk factors and symptoms suggestive of thyroid dysfunction, and test when warranted.For example: unusual fatigue, unexpected weight loss or gain, menstrual irregularities, goiter. |
Diagnose
- CTFPHC Canadian Task Force on Preventive Health Care
- CWC Choosing Wisely Canada
- INESSS Institut national d'excellence en santé et services sociaux
| Decision | Guideline |
|---|---|
| First test | TSHIt is the first-line test of thyroid function. Thyroid dysfunction is diagnosed from an abnormal TSH. |
| Free T4 | Second line, when TSH is abnormalTo grade severity and to follow hypothyroidism or hyperthyroidism. Not a first-line test to diagnose primary thyroid dysfunction. |
| Free T4 with a normal TSH | Rarely indicatedConsider it only with strong clinical suspicion, based on specific, clear and persistent symptoms of hypothyroidism or hyperthyroidism. |
| Central causes | Free T4 is indicated when central hypothyroidism (pituitary disease) or thyroid hormone resistance is suspected, and to diagnose and follow it.TSH becomes unreliable in suspected or known pituitary or hypothalamic disease. INESSS 2026 opens in a new tabChoosing Wisely Canada, CSEM opens in a new tab |
| Drugs that change TSH | Amiodarone, dopamine antagonists, immune checkpoint inhibitorsThey can affect TSH secretion and may call for a free T4. |
| Severe illness | No free T4 method is fully reliable during severe illness. |
Investigate
- CWC Choosing Wisely Canada
- INESSS Institut national d'excellence en santé et services sociaux
| Decision | Guideline |
|---|---|
| Thyroid ultrasound | Not routine for abnormal thyroid function testsOnly with a palpable abnormality, such as a large goiter or a lumpy thyroid. Incidental nodules are common and can divert the workup. |
| Cause of thyrotoxicosis | Thyroid scan, not ultrasoundTo find the cause and look for focal autonomy in a nodule. |
| Anti-TPO | Not routineOften positive in people without thyroid disease. Rarely changes management. Once thyroid autoimmunity is diagnosed, repeat testing is rarely needed. Euthyroid pregnancy at high risk of thyroid disease: It may change how often thyroid function is checked. |
| Free T4, specialist or urgent | May be considered for:Myxedema coma Immune checkpoint inhibitor therapy Follow-up of children with thyroid cancer Pregnancy at risk of obstetric complications, or with known thyroid disease |
Follow-up
- CWC Choosing Wisely Canada
- INESSS Institut national d'excellence en santé et services sociaux
| Decision | Guideline |
|---|---|
| Primary hypothyroidism on levothyroxine | Follow and adjust with TSHDo not use free T4 or T3 to monitor or adjust the dose. INESSS 2026 opens in a new tabChoosing Wisely Canada, CSEM opens in a new tab |
| Normal TSH | Adequate replacement dose in most people. |
| Pituitary or hypothalamic disease | TSH is not enough when this disease is suspected or known.Free T4 is indicated to follow central hypothyroidism. Choosing Wisely Canada, CSEM opens in a new tabINESSS 2026 opens in a new tab |
| Hyperthyroidism, after starting treatment | Free T4 is indicated for the initial follow-up of treatment. |
Pregnancy and trying to conceive
- SOGC Society of Obstetricians and Gynaecologists of Canada
- INESSS Institut national d'excellence en santé et services sociaux
| Decision | Guideline |
|---|---|
| Free T4 in pregnancy | Pregnancy changes free T4 levels, and results can be mistaken for thyroid disease. |
| After recurrent pregnancy loss | |
| Who | 2 or more pregnancy losses, including non-consecutive and biochemical losses. |
| On levothyroxine, trying to conceive | Target TSH under 2.5 (strong recommendation, high certainty). |
| Positive pregnancy test | Add 2 extra levothyroxine doses a weekKeep TSH under 2.5. Check TSH every 4-6 weeks. |
| Anti-TPO with a normal TSH | Does not change thyroid managementDecide on TSH, not on anti-TPO alone. |
Reviewed 17 October 2026 against the official sources below.
Sources
Blue square: Québec · red round: Canada. The code names the body; each section's key gives its full name.