From the Guidelines
A low TSH workup should begin with confirming the result and measuring FT4 levels to determine if the patient has clinical hyperthyroidism or central hypothyroidism, as indicated by the 2021 ASCO guideline update 1. When evaluating a patient with low TSH, it is essential to consider the clinical context, including symptoms and medication use, such as immune checkpoint inhibitor therapy.
Initial Evaluation
- Obtain a complete history, including symptoms of hyperthyroidism or hypothyroidism, and family history of thyroid disorders.
- Physical examination should focus on thyroid size, tenderness, nodules, and signs of hyperthyroidism or hypothyroidism.
- Measure FT4 levels to help interpret the low TSH result, as TSH may not accurately reflect thyroid function in all cases 1.
Additional Testing
- Consider thyroid antibodies (anti-TPO, TSI, TRAb) to identify autoimmune causes like Graves' disease.
- Thyroid ultrasound to evaluate for nodules or inflammation.
- If central hypothyroidism is suspected, evaluate as per hypophysitis, as recommended in the 2021 ASCO guideline update 1.
Management
- For asymptomatic patients with low TSH and normal FT4, continue monitoring TSH and FT4 every 4-6 weeks, as part of routine care 1.
- For symptomatic patients or those with TSH elevation, consider endocrine consultation and prescribe thyroid hormone supplementation as needed, with monitoring of TSH every 6-8 weeks while titrating hormone replacement to goal of TSH within the reference range 1.
From the Research
Low TSH Workup
When approaching a low TSH level, it is essential to consider various factors before making a diagnosis.
- A low serum level of thyrotropin (thyroid-stimulating hormone, TSH) can be associated with conditions other than a hyperthyroid state, as well as some drugs 2.
- The degree of TSH suppression plays a role in the evaluation, with levels ranging from slightly low (0.1-0.4 microIU/mL) to frankly suppressed (< 0.1 microIU/mL) 2.
Diagnosis and Treatment
Diagnosis of hypothyroidism, which can be related to low TSH levels, relies on simple testing of TSH levels and confirmation with levels of thyroxine 3.
- Management of hypothyroidism usually involves monotherapy with levothyroxine taken on an empty stomach 3.
- Follow-up involves regular assessment of TSH levels and symptom relief, with some patients potentially needing referral for specialist treatment 3.
Considerations
It is crucial to understand that hypothyroidism can have various clinical manifestations, ranging from life-threatening to no signs or symptoms, and its definition is based on statistical reference ranges of biochemical parameters 4.
- The epidemiology, causes, and symptoms of hypothyroidism, as well as evidence on diagnosis, long-term risk, treatment, and management, are essential considerations in patient care 4.