Is a Thyroid-Stimulating Hormone (TSH) level of 0.23 considered low, indicating hyperthyroidism?

TSH 0.23: Clinical Significance and Management

Yes, a TSH of 0.23 mIU/L is considered depressed and falls below the normal reference range of 0.45-4.12 mIU/L, indicating subclinical hyperthyroidism if free T4 and T3 are normal, or overt hyperthyroidism if thyroid hormones are elevated. 1

Understanding the TSH Value

Your TSH of 0.23 mIU/L sits in the "mildly suppressed" category (between 0.1-0.45 mIU/L), which is distinct from severely suppressed TSH (<0.1 mIU/L). 1, 2 This distinction matters significantly for both diagnosis and risk stratification.

The normal reference range for TSH is 0.45-4.12 mIU/L based on disease-free populations, making your value clearly below normal. 1 The geometric mean TSH in healthy individuals is 1.4 mIU/L, so your value represents substantial suppression from the population average. 1

What This TSH Level Means

The clinical significance depends entirely on your free T4 and T3 levels, which must be measured to complete the diagnosis:

• If free T4 and T3 are elevated: You have overt hyperthyroidism, which affects 0.2-1.4% of people worldwide and requires treatment. 3

• If free T4 and T3 are normal: You have subclinical hyperthyroidism, affecting 0.7-1.4% of people worldwide. 3 Treatment decisions depend on your age, symptoms, and cardiovascular/bone health risk factors. 1, 2

Common Causes to Consider

The most likely explanations for your low TSH include:

• Graves' disease (most common cause, affecting 2% of women and 0.5% of men globally) 3
• Toxic nodular thyroid disease (autonomous thyroid nodules) 2, 3
• Thyroiditis in the hyperthyroid phase (transient, often from Hashimoto's) 2
• Excessive levothyroxine therapy if you're taking thyroid hormone replacement 1, 4
• Medications including dopamine, glucocorticoids, or amiodarone 2
• Non-thyroidal illness (euthyroid sick syndrome), though undetectable TSH (<0.01 mIU/L) is rare without concurrent glucocorticoids or dopamine 1, 2
• Normal pregnancy (especially first trimester) 1, 2

Critical Next Steps

Do not make treatment decisions based on this single TSH value alone. 2, 5

1. Measure free T4 and T3 immediately on the same blood sample to distinguish subclinical from overt hyperthyroidism. 1, 2, 6

2. Repeat TSH testing in 3-6 weeks if initial workup suggests subclinical hyperthyroidism, as 30-60% of mildly abnormal values normalize spontaneously. 2, 5

3. Check TSH receptor antibodies if Graves' disease is suspected based on clinical presentation (diffuse goiter, eye findings, or family history). 3

4. Consider thyroid ultrasound and scintigraphy if nodules are palpable or etiology remains unclear after initial testing. 3

Risk Assessment Based on TSH Level

Your TSH of 0.23 mIU/L carries intermediate risk compared to severely suppressed TSH:

• Atrial fibrillation risk: Older adults (>60 years) with low TSH have a 3-fold increased risk over 10 years, though risk is highest when TSH <0.1 mIU/L. 2

• Bone health: Postmenopausal women face increased fracture risk, particularly with TSH <0.1 mIU/L, though your level of 0.23 carries lower but still elevated risk. 4

• Cardiovascular effects: Low TSH increases heart rate, left ventricular mass, and cardiac contractility, which can manifest as palpitations or other cardiac symptoms. 2

When Treatment Is Recommended

Treatment is generally recommended if:

• You have overt hyperthyroidism (elevated free T4/T3) regardless of TSH level 3
• You are >65 years old with persistent TSH <0.1 mIU/L 3
• You have osteoporosis or high fracture risk with persistent TSH suppression 4
• You have atrial fibrillation or significant cardiac disease 4, 2
• You are taking excessive levothyroxine (reduce dose by 12.5-25 mcg) 4

Treatment is typically not recommended if:

• TSH is between 0.1-0.45 mIU/L with normal free T4/T3 in younger, asymptomatic patients 2
• The cause is transient thyroiditis (observe with supportive care) 3
• Non-thyroidal illness is the underlying cause 2

Important Caveats

A low TSH alone has poor positive predictive value (only 12%) for true hyperthyroidism in older adults. 6 When combined with free T4 measurement, the predictive value increases to 67%. 6 This is why measuring thyroid hormones is essential before making any diagnosis.

In one large study of ambulatory persons over 60 years, 3.9% had TSH <0.1 mIU/L, but only 12% of these actually had hyperthyroidism. 6 The remainder were euthyroid or taking thyroid hormone. 6

If you are taking levothyroxine: Approximately 25% of patients on thyroid hormone replacement are unintentionally maintained on doses high enough to suppress TSH, increasing risks for atrial fibrillation, osteoporosis, and cardiac complications. 4 Your dose should be reduced by 12.5-25 mcg if you have no indication for TSH suppression (such as thyroid cancer). 4