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The TSH target range calculator provides indication-specific thyroid-stimulating hormone targets to guide levothyroxine dose titration and thyroid function monitoring. TSH (thyroid-stimulating hormone) is the primary biochemical parameter for monitoring thyroid hormone therapy because it integrates thyroid hormone status through the highly sensitive pituitary feedback loop. However, the appropriate TSH target differs substantially across clinical situations — a target appropriate for routine primary hypothyroidism management may be inadequate for pregnant women in the first trimester and overly suppressive for elderly patients at risk of cardiovascular complications. The key target ranges are: primary hypothyroidism in most adults — TSH 0.5-2.5 mU/L (sometimes stated as 0.5-2.0 mU/L by stricter guidelines); subclinical hypothyroidism — same target of 0.5-2.5 mU/L when treatment is initiated; first trimester of pregnancy — TSH 0.1-2.5 mU/L (stricter to protect fetal brain development); second and third trimesters — TSH 0.2-3.0 mU/L; differentiated thyroid cancer, low-risk — TSH 0.5-2.0 mU/L (low-normal, not suppressed); differentiated thyroid cancer, intermediate risk — TSH 0.1-0.5 mU/L (mild suppression for 5 years after remission); differentiated thyroid cancer, high risk or active disease — TSH below 0.1 mU/L (full suppression). Understanding the rationale for these different targets — oncological benefit, fetal protection, and avoidance of chronic over-replacement — is essential for safe and effective thyroid management.
TSH target = indication-specific range: Primary hypo (non-pregnant): 0.5-2.5 mU/L; Pregnancy T1: 0.1-2.5 mU/L; Low-risk DTC: 0.5-2.0 mU/L; Intermediate-risk DTC: 0.1-0.5 mU/L; High-risk DTC (active): <0.1 mU/L
- 1Identify the primary indication for levothyroxine therapy: primary hypothyroidism, pregnancy, subclinical hypothyroidism, or post-thyroidectomy for differentiated thyroid cancer.
- 2For primary hypothyroidism: target TSH 0.5-2.5 mU/L. For elderly patients (>70 years), a slightly higher target of 1.0-4.0 mU/L may be appropriate to avoid the risks of TSH suppression.
- 3For pregnancy: apply trimester-specific targets. First trimester 0.1-2.5 mU/L (hCG stimulates thyroid and normally suppresses TSH; target the lower part of this range). Second and third trimesters: 0.2-3.0 mU/L.
- 4For differentiated thyroid cancer (DTC) post-thyroidectomy and RAI: apply ATA risk stratification. Low-risk (excellent response to therapy): TSH 0.5-2.0 mU/L. Intermediate-risk: TSH 0.1-0.5 mU/L for 5 years. High-risk/structural disease: TSH below 0.1 mU/L.
- 5For central hypothyroidism: TSH cannot be used as a target. Target FT4 in the mid-normal range (typically 14-18 pmol/L) and assess symptoms.
- 6Re-evaluate the target periodically: a DTC patient who achieves excellent biochemical and imaging remission at 5 years may be de-escalated from mild suppression to standard replacement targets.
- 7Ensure TSH is measured at steady state (minimum 6 weeks after any dose change) and in the same laboratory using the same assay when possible for trend monitoring.
TSH at high end of normal range — patient may still be symptomatic
While TSH 3.8 mU/L is within the conventional laboratory reference range (0.4-4.0), it is above the recommended treatment target of 0.5-2.5 mU/L. Many patients remain symptomatic at this level. A small dose increase (typically 25 mcg) with TSH recheck at 6-8 weeks is appropriate.
First-trimester TSH above 2.5 mU/L requires immediate dose increase — fetal brain development at risk
In the first trimester, levothyroxine requirements increase by 25-50% due to rising hCG (which stimulates the thyroid) being insufficient to suppress TSH to appropriate pregnancy levels in hypothyroid women. A TSH of 3.1 mU/L in the first trimester is above target and requires urgent dose increase. Even a few weeks of inadequate replacement can impair fetal neurodevelopment.
No benefit from continued TSH suppression in low-risk DTC with excellent remission
Current ATA guidelines recommend that low-risk DTC patients who achieve excellent biochemical remission should have their TSH target relaxed to the low-normal range (0.5-2.0 mU/L). Continued TSH suppression at 0.3 mU/L provides no additional oncological benefit and increases the risk of atrial fibrillation and osteoporosis.
Active metastatic disease requires full TSH suppression — current dose insufficient
TSH is a growth factor for differentiated thyroid cancer. In patients with active structural disease (metastases), full TSH suppression (below 0.1 mU/L) is recommended to slow disease progression. This patient's TSH of 0.6 mU/L is well above target; a significant levothyroxine dose increase is required.
Optimising levothyroxine dosing in primary hypothyroidism patients who remain symptomatic despite 'normal' TSH, where accurate tsh target range analysis through the Tsh Target Range supports evidence-based decision-making and quantitative rigor in professional workflows
Applying trimester-specific TSH targets in pregnant women with hypothyroidism to protect fetal neurodevelopment, where accurate tsh target range analysis through the Tsh Target Range supports evidence-based decision-making and quantitative rigor in professional workflows
Risk-stratifying differentiated thyroid cancer patients and setting appropriate TSH suppression targets based on disease status, where accurate tsh target range analysis through the Tsh Target Range supports evidence-based decision-making and quantitative rigor in professional workflows
De-escalating TSH suppression in DTC patients achieving excellent remission to reduce long-term cardiovascular and bone risks, where accurate tsh target range analysis through the Tsh Target Range supports evidence-based decision-making and quantitative rigor in professional workflows
Guiding TSH monitoring frequency in stable hypothyroid patients versus those undergoing active dose titration
Atrial fibrillation and TSH targets
Patients with hypothyroidism who have known atrial fibrillation or flutter should not be over-replaced with levothyroxine. Even mildly suppressed TSH (0.1-0.5 mU/L) can trigger AF in susceptible individuals. TSH should be maintained firmly within 0.5-2.5 mU/L, and symptoms of hyperthyroidism (palpitations, tremor) should be reassessed at every visit.
Osteoporosis and TSH suppression
Chronic TSH suppression in thyroid cancer patients (particularly postmenopausal women) accelerates bone turnover and reduces bone mineral density. All patients on long-term TSH suppression should have baseline and periodic DEXA scans, calcium and vitamin D supplementation, and bisphosphonate therapy if indicated. The risk-benefit of continued suppression should be reassessed annually.
TSH in hypothyroid patients with psychiatric illness
Some patients with treatment-resistant depression or bipolar disorder are prescribed supraphysiological levothyroxine doses (e.g., 250-500 mcg/day) with intentional TSH suppression as augmentation strategy. This is an off-label adjunctive psychiatric treatment supported by some open-label evidence but not established RCT evidence, and requires very close endocrine monitoring for adverse effects.
Assay platform changes and TSH targets
When a laboratory changes its TSH immunoassay platform, the reference range and absolute TSH values may shift. A patient with a previously well-controlled TSH of 1.8 mU/L on the old platform may appear to have a TSH of 2.2 mU/L on the new platform due to calibration differences. Clinical decisions should incorporate knowledge of assay changes and comparison to the patient's individual trend.
| Indication | TSH Target (mU/L) | Key Rationale |
|---|---|---|
| Primary hypothyroidism — non-elderly | 0.5 - 2.5 | Reproduces healthy euthyroid population median |
| Primary hypothyroidism — elderly (>70y) | 1.0 - 4.0 | Avoids suppression risks in frail elderly |
| Pregnancy — 1st trimester | 0.1 - 2.5 | Critical fetal brain development window |
| Pregnancy — 2nd/3rd trimester | 0.2 - 3.0 | Continued fetal development but fetal thyroid active |
| Subclinical hypothyroidism (if treating) | 0.5 - 2.5 | Same target as overt if treatment indicated |
| DTC — low risk, excellent remission | 0.5 - 2.0 | Low-normal: no oncological benefit from suppression |
| DTC — intermediate risk (5y) | 0.1 - 0.5 | Mild suppression for limited period post-treatment |
| DTC — high risk / active disease | < 0.1 | Full suppression while structural disease present |
| Central hypothyroidism | FT4-guided only | TSH unreliable — target FT4 mid-normal range |
Why is the TSH target for hypothyroidism 0.5-2.5 mU/L rather than the broader lab reference of 0.4-4.0 mU/L?
The conventional TSH laboratory reference range (approximately 0.4-4.0 mU/L) is derived from a population that includes some individuals with mild thyroid disease, and the distribution is skewed. When healthy individuals with no thyroid disease are assessed, the median TSH is approximately 1.0-1.5 mU/L and 95% have values between 0.4-2.5 mU/L. Treating to TSH 0.5-2.5 mU/L aims to reproduce the naturally healthy state rather than simply keeping within a broad reference range.
Does the TSH target need to change in older adults?
Yes. TSH naturally rises with age — median TSH in octogenarians is approximately 2.0-3.0 mU/L in healthy individuals without thyroid disease. Over-treating elderly patients with hypothyroidism to achieve young adult TSH targets risks iatrogenic subclinical hyperthyroidism, which is associated with atrial fibrillation, accelerated bone loss, and mortality. A TSH target of 1.0-4.0 mU/L is generally appropriate in the over-70s.
Why does TSH suppression in thyroid cancer carry risks?
Chronic TSH suppression (TSH below 0.1 mU/L) causes equivalent biochemical effects to subclinical hyperthyroidism: increased atrial fibrillation risk (approximately 3-fold), accelerated bone turnover and osteoporosis (particularly in postmenopausal women), and left ventricular hypertrophy. These risks must be weighed against the oncological benefit of TSH suppression, which is primarily relevant in intermediate and high-risk DTC.
What is the TSH target for subclinical hypothyroidism?
If subclinical hypothyroidism is treated, the same TSH target as overt primary hypothyroidism applies: 0.5-2.5 mU/L. However, treatment of subclinical hypothyroidism is individualised. General guidance is to treat when TSH exceeds 10 mU/L, when the patient is symptomatic, when anti-TPO antibodies are positive (higher progression risk), in pregnancy or pregnancy planning, and in young women aged under 65.
How is TSH interpreted in the third trimester of pregnancy?
The first-trimester strict target of 0.1-2.5 mU/L relaxes slightly to 0.2-3.0 mU/L in the second and third trimesters, as fetal thyroid gland begins its own thyroid hormone synthesis from around 12 weeks. However, maternal euthyroidism remains important throughout pregnancy. Post-partum, levothyroxine dose often needs reduction back towards the pre-pregnancy dose and TSH should be rechecked 6-8 weeks after delivery.
How frequently should TSH be monitored on stable levothyroxine therapy?
For stable patients meeting TSH targets, annual TSH monitoring is sufficient in most adults. Thyroid cancer surveillance may require 6-monthly TSH alongside thyroglobulin and neck ultrasound. During pregnancy, TSH should be checked every 4-6 weeks in the first half of pregnancy. After any dose change, TSH should be rechecked 6-8 weeks later. Significant clinical changes (new medications, weight change, GI absorption changes) also warrant unscheduled TSH checking.
Can TSH be used as the monitoring parameter in patients on T3 (liothyronine)?
TSH can still be used as a monitoring parameter in patients receiving combination T4+T3 therapy, but with caution. Liothyronine (T3) has a short half-life and causes TSH to be variably suppressed depending on when the sample is taken relative to the T3 dose. TSH should be measured at a consistent time relative to the last T3 dose, or morning (pre-dose) sampling used. FT4 and FT3 should be measured alongside TSH in combination therapy monitoring.
What is the TSH target after total thyroidectomy for benign disease?
After total thyroidectomy for benign indications (large goitre, Graves disease, or compressive symptoms), the target is standard primary hypothyroidism replacement: TSH 0.5-2.5 mU/L. There is no oncological justification for TSH suppression. The levothyroxine dose is typically 1.6 mcg/kg/day ideal body weight, with TSH rechecked 6-8 weeks after dose initiation and then 6-12 monthly when stable.
プロのヒント
When counselling thyroid cancer patients about TSH suppression, frame the conversation in terms of risk-benefit: for low-risk patients with no evidence of disease, the risks of long-term TSH suppression (AF, osteoporosis) outweigh the minimal oncological benefit. For patients with active disease, the balance shifts — suppression is indicated. This framing helps patients understand why their target changes over time.
ご存知でしたか？
TSH was the first hormone to be measured by radioimmunoassay in clinical practice, after Rosalyn Yalow and Solomon Berson developed the technique in the late 1950s (Yalow received the Nobel Prize in 1977). Before TSH measurement, thyroid therapy was entirely symptom-guided — doctors would feel the pulse, check the skin, and ask about energy levels to estimate whether the dose was 'right'.
参考文献
- ›Jonklaas J et al. Guidelines for the Treatment of Hypothyroidism (ATA 2014). Thyroid 2014
- ›Haugen BR et al. ATA Management Guidelines for Adult Thyroid Nodules and Differentiated Thyroid Cancer 2015
- ›Alexander EK et al. 2017 ATA Guidelines on Thyroid Disease During Pregnancy and Postpartum. Thyroid 2017
- ›NICE NG145 — Thyroid Disease: Assessment and Management 2019