Interpretation of Normal Thyroid Function Tests
These thyroid function test results demonstrate normal, euthyroid thyroid status with TSH values consistently within the reference range (0.4-4.0 mU/L) and Free T4 in the normal range (9-19 pmol/L), requiring no intervention.
Serial TSH Trend Analysis
Your TSH values show a progressive increase over time while remaining within normal limits 1:
- Initial TSH: 0.83 mU/L - Lower-normal range
- Second TSH: 1.11 mU/L - Approaching population geometric mean
- Third TSH: 1.40 mU/L - At the population geometric mean (1.4 mU/L) 1
- Most recent TSH: 2.16 mU/L - Mid-normal range
The geometric mean TSH in disease-free populations is 1.4 mU/L, and the reference range (2.5th-97.5th percentile) is 0.45 to 4.12 mU/L 1. All your values fall comfortably within this range.
Free T4 Assessment
Both Free T4 measurements of 17 pmol/L are solidly within the normal reference range (9-19 pmol/L), indicating adequate thyroid hormone production 1. The combination of normal TSH with normal Free T4 definitively excludes both overt and subclinical thyroid dysfunction 1.
Clinical Significance of the TSH Trend
While your TSH has increased from 0.83 to 2.16 mU/L over the observation period, this upward trend does not indicate thyroid disease for several important reasons:
- All values remain well below the upper limit of normal (4.0-4.5 mU/L) where subclinical hypothyroidism begins 1
- TSH naturally varies due to pulsatile secretion, time of day, and physiological factors 1
- The most recent TSH of 2.16 mU/L is still below the threshold (2.5 mU/L) where some investigators suggest increased monitoring, though even values between 2.5-4.5 mU/L are not associated with adverse consequences in asymptomatic individuals 1
- Free T4 remains stable and normal, which is the definitive indicator that thyroid hormone production is adequate 1
What These Results Mean
You have normal thyroid function (euthyroid state) 2. This means:
- Your thyroid gland is producing adequate amounts of thyroid hormone 1
- Your pituitary-thyroid feedback axis is functioning normally 3, 4
- No thyroid hormone replacement therapy is indicated 5
- No further thyroid testing is needed unless symptoms develop 1
When to Recheck Thyroid Function
For asymptomatic individuals with normal thyroid function tests, routine screening intervals are not well-established 1. However, you should have thyroid function rechecked if you develop:
- Symptoms of hypothyroidism: unexplained fatigue, weight gain, cold intolerance, constipation, dry skin, hair loss, or depression 1
- Symptoms of hyperthyroidism: unexplained weight loss, palpitations, heat intolerance, tremor, anxiety, or diarrhea 1
- Risk factors emerge: starting medications that affect thyroid function (amiodarone, lithium, immune checkpoint inhibitors), pregnancy, or development of other autoimmune conditions 1, 5
Important Caveats
TSH values can be transiently affected by 1:
- Acute illness or hospitalization (euthyroid sick syndrome) 1
- Recent iodine exposure from CT contrast 5
- Certain medications (dopamine, glucocorticoids, dobutamine) 1
- Recovery phase from thyroiditis 1, 5
The 37% spontaneous normalization rate observed in studies of mildly elevated TSH underscores why single abnormal values should not trigger treatment, and why your consistently normal values are reassuring 1.
Bottom Line
Your thyroid function is completely normal, and no action is needed 1, 2. The gradual TSH increase from 0.83 to 2.16 mU/L represents normal physiological variation within the reference range and does not predict future thyroid disease 1. Continue routine health maintenance and only recheck thyroid function if symptoms develop.