Ajax Harwood Clinic

Thyroid testing: should I be tested?

Last reviewed 2026-09-23Content v3f9e04e515b5
Reference tool — not medical advice. Clinician judgement always required.

Hypothyroidism

Defined testing criteria

Also called: underactive thyroid, low thyroid, thyroid problems, sluggish thyroid, hypothyroid

Fatigue, weight gain, and low mood are common, and thyroid disease is a well-known, easily testable cause, so patients, sometimes prompted by an ND or a privately purchased 'full thyroid panel,' want to know whether their thyroid explains how they feel, especially after reading that a 'normal' TSH doesn't necessarily rule it out.

Raises suspicion

  • • New fatigue
  • • Unexplained weight gain
  • • Cold intolerance
  • • Dry skin
  • • Hair thinning or loss
  • • Constipation
  • • Hoarse voice
  • • Menstrual irregularity
  • • A palpable goitre or neck swelling
  • • Personal history of thyroid disease, other autoimmune disease, or neck irradiation
  • • Pregnancy planning or early pregnancy, or 6 weeks to 6 months postpartum
  • • Medications known to affect thyroid function, such as amiodarone or lithium

Does not raise suspicion

  • • Fatigue or weight change alone, with no other feature
  • • Mild, non-specific symptoms in an otherwise well patient with no risk factors
  • • General 'sluggishness' without any of the triggers above

Red flags

  • • Myxedema coma: hypothermia, altered mental status, bradycardia, and hypotension in a patient with untreated or under-treated hypothyroidism. This needs emergency assessment.
  • • Severe symptomatic bradycardia
  • • Suspected coexisting adrenal insufficiency in the same patient: check for adrenal insufficiency features before starting thyroid hormone replacement, since treating hypothyroidism first in a patient with untreated adrenal insufficiency can precipitate an adrenal crisis.

Who to test

  • Patients with symptoms or higher-risk features above: TSH (thyroid stimulating hormone) (Standard)TSH first; add free T4 only to confirm and characterize an abnormal TSH
  • Monitoring known hypothyroidism or a levothyroxine dose change: TSH (thyroid stimulating hormone) (Standard)TSH alone, checked no sooner than 4-6 weeks after a dose change

More likely instead

Counselling script

“If you have symptoms suggestive of thyroid dysfunction, or you're in a higher-risk group like pregnancy planning or the postpartum period, TSH is the right first test. If your TSH is normal, additional thyroid tests aren't needed and won't change anything. If TSH is abnormal, we'll add a free T4 in the same sample to characterize it.”

Chart snippet (OSCAR-safe plain text)

Concern discussed, not tested

Concern re: hypothyroidism discussed.
Discriminating features: fatigue, weight change, cold intolerance, dry skin, goitre, high-risk group membership; absent.
Assessment: low pre-test probability; routine screening not indicated in this patient.
Plan: no TSH ordered at this time; when to revisit reviewed with patient.
Ref: Choosing Wisely Canada thyroid screening recommendation.
Patient given info page: https://thyroid.ajaxharwoodclinic.com/patient
Revisit if: new symptoms develop, or pregnancy planning or the postpartum period begins.

Testing ordered

Concern re: hypothyroidism discussed.
Discriminating features: fatigue, weight change, cold intolerance, dry skin, goitre, high-risk group membership; some present as noted in chart.
Assessment: symptoms or risk factors support TSH testing.
Plan: TSH ordered; free T4 to follow only if TSH abnormal.
Ref: OAML thyroid testing guideline 2007; AACE/ATA hypothyroidism guideline 2012.
Patient given info page: https://thyroid.ajaxharwoodclinic.com/patient
Revisit if: symptoms persist despite a normal TSH.

Revisit if

  • • New or worsening fatigue, weight gain, or cold intolerance despite a normal TSH
  • • New neck swelling or goitre
  • • Planning pregnancy, or 6 weeks to 6 months postpartum
  • • Starting amiodarone or lithium

References

  1. 1. Ontario Association of Medical Laboratories (OAML). Guideline for the Use of Laboratory Tests to Detect Thyroid Dysfunction (CLP 015) (2007)— older guidelineTSH alone is the appropriate initial test in most situations
  2. 2. American Association of Clinical Endocrinologists / American Thyroid Association. Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association (2012)— older guidelineSymptom list and higher-risk groups for testing; a serum TSH is the single best screening test for primary thyroid dysfunction
  3. 3. College of Family Physicians of Canada / Choosing Wisely Canada. Family Medicine: Fifteen Tests and Treatments to Question (2026)Don't screen for thyroid dysfunction in asymptomatic nonpregnant adults
  4. 4. National Institute for Health and Care Excellence (NICE). Thyroid disease: assessment and management (NG145) (2019)Measure TSH alone unless secondary (pituitary) thyroid dysfunction is suspected
Evidence notes

[1] and [2] are flagged older_than_10y (2007, 2012), but they remain the operative Ontario laboratory-utilization and North American clinical guidance; the more recent NICE NG145 (2019) is concordant, so no material superseding guidance was found. Myxedema coma red-flag features are standard content of hypothyroidism management guidelines [2] but were not separately re-quoted in this batch beyond the on-file verbatim quote; this is confident physiology rather than an independently sourced claim, flagged here rather than fabricated as a direct quote. Tag rationale: A, not borderline. TSH is a well-validated single screening test with defined thresholds. Note for reconciliation: the linked test records (tsh, Free T4 (thyroxine), Free T3 (triiodothyronine), Thyroid peroxidase antibodies (TPOAb), Full thyroid panel (TSH, free T4, free T3, reverse T3, thyroid antibodies), Reverse T3 (rT3)) use the generic condition id 'thyroid' in their linked_conditions field rather than 'hypothyroidism'; this batch defines the anchor condition id as 'hypothyroidism' per the operator's instructions, so the lint check will warn that 'thyroid' is not (yet) a condition id. Recommend reconciling on merge, either by adding a 'thyroid' alias/redirect or updating tests.json.

Hashimoto's thyroiditis with a normal TSH

Defined testing criteria

Also called: Hashimoto's, Hashimoto's thyroiditis, autoimmune thyroiditis, positive thyroid antibodies, TPO antibodies positive, euthyroid Hashimoto's

Patients sometimes have thyroid antibodies checked, often through an ND panel, and are told they have 'Hashimoto's' based on a positive TPO antibody alone, even with a normal TSH, and want to know what that means and whether they need treatment.

Raises suspicion

  • • TSH above the reference range, even mildly (subclinical hypothyroidism), with positive TPO antibodies: raises the likelihood of progression to overt hypothyroidism
  • • A goitre with positive TPO antibodies
  • • Family history of autoimmune thyroid disease plus a mildly elevated TSH
  • • Pregnancy planning or early pregnancy with a borderline TSH, where thyroid autoimmunity affects risk assessment

Does not raise suspicion

  • • A positive TPO antibody with a completely normal TSH and no symptoms: this indicates autoimmune susceptibility, not current thyroid dysfunction, and does not by itself mean treatment is needed or that current symptoms are explained by it

Red flags

  • • A rapidly enlarging goitre, or a firm or asymmetric thyroid nodule: consider other thyroid pathology, not routine Hashimoto's thyroiditis

Who to test

More likely instead

Counselling script

“A positive TPO antibody with a normal TSH means your immune system is active against your thyroid, but your thyroid is currently functioning normally, so it doesn't need treatment now. If your TSH is also mildly elevated, that combination raises the chance of progressing to hypothyroidism, and we'd talk about monitoring or treatment. Repeating the antibody test itself isn't useful, since once positive, it stays positive.”

Chart snippet (OSCAR-safe plain text)

Concern discussed, not tested

Concern re: Hashimoto's thyroiditis discussed, raised after ND-ordered antibody testing.
Discriminating features: TSH elevation, goitre, family history, pregnancy planning; reviewed.
Assessment: positive TPO antibody with normal TSH, consistent with autoimmune susceptibility and no current thyroid dysfunction.
Plan: no treatment indicated; periodic TSH monitoring discussed; repeat antibody testing not useful.
Ref: NICE thyroid disease guideline NG145 2019; Whickham survey 20-year follow-up 1995.
Patient given info page: https://thyroid.ajaxharwoodclinic.com/patient
Revisit if: symptoms of hypothyroidism develop, or a repeat TSH becomes abnormal.

Testing ordered

Concern re: Hashimoto's thyroiditis discussed.
Discriminating features: TSH elevation present.
Assessment: subclinical or overt hypothyroidism with a positive TPO antibody supports Hashimoto's thyroiditis as the cause and informs the monitoring or treatment decision.
Plan: TSH and TPO antibody ordered or reviewed; follow-up TSH planned.
Ref: NICE thyroid disease guideline NG145 2019; AACE/ATA hypothyroidism guideline 2012.
Patient given info page: https://thyroid.ajaxharwoodclinic.com/patient
Revisit if: symptoms progress, or TSH continues to rise on monitoring.

Revisit if

  • • New symptoms of hypothyroidism
  • • TSH becomes abnormal on periodic recheck
  • • Pregnancy planning or a new pregnancy
  • • New or enlarging goitre

References

  1. 1. National Institute for Health and Care Excellence (NICE). Thyroid disease: assessment and management (NG145) (2019)TPO antibody testing to identify autoimmune thyroiditis as the cause of an abnormal TSH and to help predict progression
  2. 2. American Association of Clinical Endocrinologists / American Thyroid Association. Clinical practice guidelines for hypothyroidism in adults: cosponsored by the American Association of Clinical Endocrinologists and the American Thyroid Association (2012)— older guidelineTPO antibody status informs the treat-versus-monitor decision in subclinical hypothyroidism
  3. 3. Clinical Endocrinology (Whickham Survey twenty-year follow-up). The incidence of thyroid disorders in the community: a twenty-year follow-up of the Whickham Survey (1995)— older guidelinePositive TPO antibody with an elevated TSH predicts progression to overt hypothyroidism, from a 20-year population follow-up
  4. 4. Ontario Association of Medical Laboratories (OAML). Guideline for the Use of Laboratory Tests to Detect Thyroid Dysfunction (CLP 015) (2007)— older guidelineContext for the TSH-first testing strategy this condition sits within
Evidence notes

[3] is the foundational natural-history data (20-year Whickham Survey follow-up) and is flagged older_than_10y (1995); it remains the standard-cited source for TPO-antibody-positive progression risk in current guidelines, including NICE NG145 and AACE/ATA, so it is included despite its age rather than treated as superseded. Tag rationale: A, not borderline. TSH plus TPO antibody are well-defined, guideline-supported tests, though what a positive antibody with a normal TSH means is a nuance worth explaining carefully so patients don't read a positive antibody alone as a diagnosis requiring treatment.

Popular labels: what they mean

"Low T3" / reverse T3 dominance

Not a recognized medical diagnosis

Also called: low T3, reverse T3 dominance, poor T4-to-T3 conversion, Wilson's temperature syndrome, hypothyroid with normal labs, T3 conversion problem, high reverse T3

Patients who feel unwell despite a normal TSH, or who remain symptomatic on levothyroxine, sometimes encounter the idea that their body isn't 'converting' T4 to T3 properly, or that a high reverse T3 is 'blocking' their active thyroid hormone. This is often framed as 'Wilson's temperature syndrome,' assessed with low basal body temperature and a reverse T3 to free T3 ratio, and treated with compounded or sustained-release T3. The concern is understandable: persistent symptoms despite normal-looking labs deserve to be taken seriously, and a genuine subset of patients on levothyroxine do report ongoing symptoms.

Raises suspicion

  • • This label itself has no discriminating features, because it is not a validated diagnostic category. What does deserve a real look: a patient remaining symptomatic on an adequate dose of levothyroxine with a normal TSH, where a discussion of the evidence around combination T4/T3 therapy is reasonable, or symptoms and signs that instead suggest a different real condition (see the hypothyroidism or adrenal pages).

Does not raise suspicion

  • • Low basal body temperature alone
  • • A reported 'high reverse T3' or an abnormal reverse T3 to free T3 ratio on a panel
  • • Fatigue, brain fog, or weight gain with a normal TSH and free T4

Red flags

  • • Palpitations, chest pain, or a rapid heart rate in someone taking unsupervised compounded or high-dose T3: needs urgent review, since T3 dosed outside standard guidance can cause cardiac arrhythmia or accelerated bone loss

Who to test

  • Patients remaining symptomatic on levothyroxine with a normal TSH: Free T3 (triiodothyronine) (Situation-specific)Not to diagnose 'low T3'; only relevant if suspected secondary hypothyroidism or T3 toxicosis is otherwise being worked up. Reverse T3 (no validated clinical use) is not recommended.
  • Anyone who already has a reverse T3 result showing an abnormal valueReverse T3 has no validated clinical use; an abnormal result should not by itself change management or prompt further testing

More likely instead

Counselling script

“'Low T3' or 'Wilson's temperature syndrome,' based on reverse T3 or body temperature, isn't a recognized diagnosis, and reverse T3 testing isn't recommended by any guideline reviewed for this record. If you're on levothyroxine and still symptomatic with a normal TSH, that's worth discussing. There's real research interest in combination T4/T3 therapy for persistent symptoms, though trials haven't consistently shown a benefit. I wouldn't recommend compounded T3 dosed by temperature readings, since that approach can cause harm.”

Chart snippet (OSCAR-safe plain text)

Concern discussed, not tested

Concern re: 'low T3' or reverse T3 dominance discussed, raised by patient or ND.
Discriminating features: none identified; not a recognized diagnosis.
Assessment: reverse T3 and body-temperature-based testing have no validated diagnostic use.
Plan: no reverse T3 ordered; TSH reviewed and normal; evidence on combination T4/T3 therapy for persistent symptoms on levothyroxine discussed.
Ref: Annals of Clinical and Laboratory Science reverse T3 report 2020; ATA/BTA/ETA combination therapy consensus 2021; American Thyroid Association statement on Wilson's syndrome.
Patient given info page: https://thyroid.ajaxharwoodclinic.com/patient
Revisit if: new symptoms suggestive of a real thyroid, adrenal, or other condition develop.

Revisit if

  • • Persistent symptoms despite a normal TSH and adequate levothyroxine adherence: reasonable to discuss combination T4/T3 therapy as an evidence-based option, not reverse T3 testing
  • • New palpitations or a rapid heart rate while taking any T3 preparation: urgent review
  • • Symptoms suggestive of a different real condition, such as adrenal, iron, sleep, or mood

References

  1. 1. Association of Clinical Scientists (Annals of Clinical & Laboratory Science). Trust your Endocrinologist – Report and Recommendations on the Ordering of Reverse T3 Testing (2020)Reverse T3's diagnostic utility for this indication is questionable and testing is not recommended by any professional practice guideline
  2. 2. American Thyroid Association. Guidelines for the treatment of hypothyroidism: prepared by the American Thyroid Association task force on thyroid hormone replacement (2014)— older guideline2014 ATA treatment guideline context on levothyroxine and alternative thyroid hormone preparations
  3. 3. American Thyroid Association / British Thyroid Association / European Thyroid Association. Evidence-Based Use of Levothyroxine/Liothyronine Combinations in Treating Hypothyroidism: A Consensus Document (2021)Fourteen clinical trials have not shown a consistent benefit of LT4/LT3 combination therapy, though the panel found equipoise for a future clinical trial in patients dissatisfied on LT4 monotherapy
  4. 4. American Thyroid Association. American Thyroid Association Statement on "Wilson's Syndrome" (2005)— older guidelineATA statement that prescribing T3 for 'Wilson's syndrome' is inconsistent with normal physiology and represents a potential hazard, and that no evidence supports the syndrome's existence
Evidence notes

[4] is flagged older_than_10y (2005); no more recent ATA statement rescinding or updating it was found, and it remains published as the standing professional-body position on the ATA's current website, so it is treated as current guidance rather than superseded. [2] is also flagged older_than_10y; the more recent [3] consensus supersedes it specifically for the combination-therapy question and is the primary source used for that claim. Tag rationale: C, not borderline. 'Low T3 syndrome' and 'Wilson's temperature syndrome' rest on a physiological model (reverse T3 'blocking' T3 action, and a 98.6F normal-body-temperature assumption) that professional societies have explicitly rejected. The one genuinely open clinical question, whether combination T4/T3 therapy helps patients who remain symptomatic on levothyroxine with a normal TSH, is real and unresolved, and is presented as such here rather than folded into the rejection of the C-label.

General clinical reference for Ajax Harwood Clinic. Not medical advice, and not a substitute for individualized clinical assessment.