Understanding Subclinical Hypothyroidism: A Simple Guide
What Is Subclinical Hypothyroidism?
Subclinical hypothyroidism means your thyroid gland is starting to underperform, but hasn't completely failed yet. Your blood test shows an elevated TSH (thyroid-stimulating hormone) level, but your thyroid hormone levels (T4 and T3) are still normal 1, 2. Think of TSH as your body's alarm system—when it's elevated, your body is working harder to get your thyroid to produce enough hormone 1.
This condition is very common, affecting up to 10% of adults 2. It's most often caused by an autoimmune condition called Hashimoto's thyroiditis, where your immune system gradually damages your thyroid gland 2.
What Does This Mean for You?
- Your thyroid is struggling but still keeping up—for now 1, 2
- You may or may not have symptoms like fatigue, weight gain, cold intolerance, or constipation 1
- Without treatment, about 2-5% of people progress to full hypothyroidism each year 3, 2
- If you have positive thyroid antibodies (anti-TPO), your risk of progression is higher—about 4.3% per year versus 2.6% without antibodies 1, 4
Will You Need Treatment?
Treatment depends mainly on how high your TSH level is 1:
You WILL Need Treatment If:
- Your TSH is above 10 mIU/L—treatment is recommended regardless of symptoms 1, 3, 2
- You are pregnant or planning pregnancy—any TSH elevation should be treated 1, 3
- You have symptoms of hypothyroidism (fatigue, weight gain, cold intolerance) 1, 2
You May NOT Need Treatment If:
- Your TSH is between 4.5-10 mIU/L and you have no symptoms 1, 5
- You are over 85 years old with mild TSH elevation 3
- Your TSH elevation may be temporary (30-60% of mildly elevated TSH levels return to normal on their own) 1, 5
What Happens Next: Your Follow-Up Plan
If You're NOT Starting Treatment:
Recheck your thyroid function in 3-6 months 1:
- Your doctor will measure TSH and free T4 again
- If TSH remains elevated, you may need treatment
- If TSH normalizes, continue monitoring every 6-12 months 1
Watch for symptoms that might indicate worsening thyroid function 1:
- Increasing fatigue or weakness
- Unexplained weight gain
- Feeling cold when others are comfortable
- Constipation
- Dry skin or hair loss
- Depression or difficulty concentrating
If You ARE Starting Treatment:
You'll take levothyroxine (thyroid hormone replacement) 1, 6:
- Take it on an empty stomach, 30-60 minutes before breakfast with a full glass of water 6
- Don't take it within 4 hours of iron, calcium supplements, or antacids—these block absorption 6
- Take it at the same time every day for consistent levels 6
Initial monitoring is frequent 1:
- Recheck TSH and free T4 every 6-8 weeks while adjusting your dose
- Your doctor will adjust the dose by small amounts (12.5-25 mcg) until TSH normalizes 1
- Target TSH range is typically 0.5-4.5 mIU/L 1
Once stable, monitoring becomes less frequent 1:
- TSH checked every 6-12 months
- More frequent checks if symptoms change or you start new medications
Important Things to Know
It may take several weeks to feel better 6. The medication needs time to build up in your system and for your body to adjust.
This is usually lifelong treatment 6. Most people with hypothyroidism need to take thyroid hormone replacement for the rest of their lives.
Notify your doctor if you experience 6:
- Rapid or irregular heartbeat
- Chest pain or shortness of breath
- Severe headache or nervousness
- Tremors or excessive sweating
- Any unusual symptoms
Special situations requiring immediate notification 1:
- If you become pregnant (thyroid hormone needs increase during pregnancy)
- Before any surgery
- If you develop new heart problems
The Bottom Line
Subclinical hypothyroidism is a mild form of thyroid underactivity that may or may not need treatment depending on your TSH level, symptoms, and individual circumstances 1, 2. Your doctor will help determine the best approach for you, with regular monitoring to catch any changes early 1.