From the Guidelines
To evaluate a thyroid panel, focus on TSH levels, particularly those between 4.5 and 10 mIU/L, as some individuals with these levels may exhibit symptoms compatible with hypothyroidism, and consider a trial of levothyroxine while monitoring for improvement in hypothyroid-type symptoms, as suggested by the guidelines for diagnosis and management of subclinical thyroid disease 1. When evaluating a thyroid panel, the following components should be considered:
- TSH levels: Normal ranges are typically between 0.4-4.0 mIU/L, but levels between 4.5 and 10 mIU/L may require closer examination, as some individuals may exhibit symptoms of hypothyroidism, despite normal free T4 and free T3 levels 1.
- Free T4 and free T3 levels: These should also be evaluated, but the primary focus should be on TSH levels, particularly in cases where symptoms of hypothyroidism are present. Interpretation of results should consider the following:
- High TSH with low T4/T3: Primary hypothyroidism
- Low TSH with high T4/T3: Hyperthyroidism
- Low TSH with low T4/T3: Central hypothyroidism
- Normal TSH with abnormal T4/T3: Consider thyroid hormone resistance or assay interference It is essential to consider the clinical context, as thyroid function can be affected by medications, illness, and pregnancy, and subclinical thyroid dysfunction may require monitoring rather than immediate treatment, as the likelihood of improvement with therapy is small, and the potential risks and inconvenience of treatment must be balanced against the potential benefits 1.
From the FDA Drug Label
Assess the adequacy of therapy by periodic assessment of laboratory tests and clinical evaluation. In adult patients with primary hypothyroidism, monitor serum TSH levels after an interval of 6 to 8 weeks after any change in dosage. In patients on a stable and appropriate replacement dosage, evaluate clinical and biochemical response every 6 to 12 months and whenever there is a change in the patient’s clinical status In patients with hypothyroidism, assess the adequacy of replacement therapy by measuring both serum TSH and total or free-T4.
Evaluating a thyroid panel involves:
- Monitoring TSH levels: after an interval of 6 to 8 weeks after any change in dosage, and every 6 to 12 months in patients on a stable replacement dosage
- Measuring total or free-T4: in patients with hypothyroidism, to assess the adequacy of replacement therapy
- Clinical evaluation: periodic assessment of clinical response and evaluation of the patient's clinical status
- Laboratory tests: periodic assessment of laboratory tests, including serum TSH and total or free-T4 levels 2
From the Research
Evaluating a Thyroid Panel
Evaluating a thyroid panel involves assessing various hormone levels to determine thyroid function. The key components of a thyroid panel include:
- Thyroid-stimulating hormone (TSH)
- Free thyroxine (FT4)
- Free triiodothyronine (FT3)
- Total thyroxine (T4)
- Total triiodothyronin (T3)
- Reverse triiodothyronin (rT3)
- Thyroid antibodies, such as antithyroglobulin antibodies (ATA) and antimicrosomal antibodies (AMA) 3
Interpreting Thyroid Function Tests
Interpreting thyroid function tests requires consideration of the physiological and pathological context. The introduction of sensitive thyrotropin assays and free thyroid hormone measurements has simplified the interpretation of thyroid function tests 4. However, important pitfalls and difficult cases still exist. Thyroid function test results can be grouped into six different patterns, and knowledge of these patterns, coupled with clinical details and simple additional tests, allows a diagnosis to be made in almost all cases 4.
Choosing the Appropriate Tests
When evaluating a thyroid panel, it is essential to choose the appropriate tests. TSH is the single most appropriate test of thyroid function when screening for thyroid disorders 5, 6. Adding more tests only increases the likelihood that a minor (and often insignificant) abnormality will be found 6. Free T4 (FT4) and free T3 (FT3) measurements are used to confirm and assess the level of hypo and hyperthyroidism (overt or subclinical) 7.
Considerations in Special Cases
In certain cases, such as when the thyroidal status is unstable or when the hypothalamic-pituitary function is disturbed, TSH determination may be diagnostically misleading, and only free hormone measurements are reliable for thyroid function assessment 7. Additionally, in pediatric patients, careful consideration should be given to the choice of screening test(s) for acquired thyroid dysfunction, and emphasis should be placed on the proper interpretation of the test(s) to avoid unnecessary anxiety and additional testing 6.