Should You Increase Armour Thyroid with TSH 0.45?
No, do not increase your Armour Thyroid dose with a TSH of 0.45 mIU/L—this value is at the lower end of normal and increasing the dose would risk iatrogenic hyperthyroidism with serious cardiovascular and bone complications. 1
Understanding Your Current TSH Level
Your TSH of 0.45 mIU/L sits at the very bottom of the normal reference range (0.45-4.12 mIU/L), indicating you are already receiving adequate—if not slightly excessive—thyroid hormone replacement. 2
- This TSH level does NOT indicate hypothyroidism requiring treatment. The normal reference range is 0.45-4.5 mIU/L, and your value of 0.45 is technically within normal limits. 1, 2
- Lowering TSH further would create subclinical hyperthyroidism, which occurs in 14-21% of treated patients and significantly increases risks for atrial fibrillation (3-5 fold), osteoporosis, fractures, and cardiovascular mortality. 1
Why Increasing Your Dose Would Be Dangerous
Approximately 25% of patients on thyroid hormone replacement are unintentionally maintained on doses sufficient to fully suppress TSH, exposing them to serious complications. 1
Cardiovascular Risks
- Atrial fibrillation risk increases 3-5 fold when TSH drops below 0.45 mIU/L, especially in patients over 60 years. 1
- Cardiovascular mortality increases 2.2-3 fold in individuals older than 60 years with TSH below 0.5 mIU/L. 1
- Even therapeutic doses can cause measurable cardiac dysfunction, including increased heart rate and abnormal cardiac output. 1
Bone Health Risks
- Meta-analyses demonstrate significant bone mineral density loss in postmenopausal women with TSH suppression, even at levels between 0.1-0.45 mIU/L. 1
- Women over 65 with TSH ≤0.1 mIU/L have documented increased risk of hip and spine fractures. 1
What You Should Do Instead
Confirm Your Current Status
- Repeat TSH measurement in 3-6 weeks along with free T4 to confirm this finding, as TSH can be transiently affected by acute illness, medications, time of day, and other physiological factors. 3, 4
- A single borderline TSH value should never trigger treatment decisions, as 30-60% of mildly abnormal TSH levels normalize spontaneously on repeat testing. 3
If TSH Remains 0.45 mIU/L or Lower
- Consider reducing your Armour Thyroid dose by a small amount (equivalent to 12.5-25 mcg of levothyroxine) if TSH remains in the 0.1-0.45 mIU/L range, particularly if you are elderly or have cardiac disease. 1
- Target TSH should be 0.5-2.0 mIU/L for primary hypothyroidism to avoid both under-treatment and over-treatment complications. 2
Monitor for Signs of Overtreatment
- Watch for symptoms of hyperthyroidism: palpitations, tremor, heat intolerance, weight loss, anxiety, or new-onset atrial fibrillation. 3
- If you are over 60 years old or postmenopausal, your risks from TSH suppression are substantially higher. 1
Critical Pitfalls to Avoid
- Never increase thyroid hormone based on symptoms alone when TSH is already low-normal. Many symptoms attributed to hypothyroidism (fatigue, weight changes) have multiple causes and will not improve with excessive thyroid hormone. 1
- Do not assume you need more medication because TSH is "at the bottom of normal." The entire reference range represents adequate thyroid function. 2
- Avoid checking TSH too frequently (wait at least 6-8 weeks between measurements) to prevent inappropriate dose adjustments before steady state is reached. 1
Special Considerations
If you have thyroid cancer, your target TSH may be intentionally lower (0.1-0.5 mIU/L or even <0.1 mIU/L depending on risk stratification), but this requires endocrinologist guidance and should not be self-adjusted. 1, 5
If you are taking Armour Thyroid specifically (which contains both T4 and T3), TSH may run slightly lower than with levothyroxine alone due to the T3 component, but a TSH of 0.45 still represents the lower limit of acceptable dosing. 1