What Elevated TSH Means
An elevated TSH level indicates your thyroid gland is not producing enough thyroid hormone, signaling either subclinical hypothyroidism (when free T4 remains normal) or overt hypothyroidism (when free T4 is low). 1
Understanding the Two Types of Hypothyroidism
Subclinical hypothyroidism occurs when TSH exceeds the upper threshold (typically >4.5 mIU/L) but thyroxine (T4) levels remain within the normal range, often without symptoms 1. This represents early thyroid failure where your pituitary gland is working harder to stimulate adequate hormone production 2.
Overt hypothyroidism is defined by both elevated TSH and low T4 levels, regardless of whether symptoms are present 1. This indicates your thyroid gland has failed to meet your body's hormone requirements despite maximal pituitary stimulation 2.
Clinical Significance Based on TSH Level
The degree of TSH elevation determines urgency and treatment approach:
- TSH >10 mIU/L strongly indicates significant thyroid dysfunction requiring prompt treatment, carrying approximately 5% annual risk of progression to overt hypothyroidism 3, 1
- TSH 4.5-10 mIU/L represents milder dysfunction where approximately 37% of cases spontaneously normalize without intervention 3, 1
- Severely elevated TSH (>10 mIU/L) warrants immediate levothyroxine therapy regardless of symptoms 3
Most Common Cause
Chronic lymphocytic thyroiditis (Hashimoto's thyroiditis) is the most common cause of elevated TSH in adults, an autoimmune condition where your immune system attacks the thyroid gland 2. The presence of anti-thyroid peroxidase (anti-TPO) antibodies confirms this autoimmune etiology and predicts a higher progression risk to overt hypothyroidism (4.3% per year versus 2.6% in antibody-negative individuals) 3.
Symptoms Associated with Elevated TSH
Many patients with mildly elevated TSH remain asymptomatic, especially with subclinical hypothyroidism 1. When symptoms occur, they typically include:
- Fatigue and weakness 3
- Weight gain despite normal eating 3
- Cold intolerance 3
- Constipation 3
- Dry skin and hair loss 2
- Cognitive slowing or difficulty concentrating 3
Critical Confirmation Steps Before Treatment
Never treat based on a single elevated TSH value—confirm with repeat testing after 3-6 weeks, as 30-60% of elevated TSH levels normalize spontaneously 3. This high rate of spontaneous normalization reflects transient thyroiditis, recovery from acute illness, or normal physiological variation 3.
When TSH remains elevated on repeat testing, measure free T4 to distinguish subclinical from overt hypothyroidism 3, 2. Consider checking anti-TPO antibodies to identify autoimmune etiology, which influences treatment decisions and predicts progression risk 3.
Important Caveats
Laboratory reference intervals for TSH are based on statistical distribution rather than clinical outcomes, leading to professional disagreement about appropriate treatment thresholds 1. TSH values can be transiently affected by acute illness, hospitalization, recent iodine exposure (such as CT contrast), certain medications, or recovery from thyroiditis 3.
In patients with suspected central hypothyroidism (pituitary or hypothalamic disease), TSH may be inappropriately normal or only mildly elevated despite low free T4 4. In these cases, TSH cannot be used as a reliable screening test, and free T4 measurement becomes essential 4.
When Elevated TSH Requires Immediate Action
Rule out concurrent adrenal insufficiency before starting thyroid hormone replacement—initiating levothyroxine before corticosteroids can precipitate life-threatening adrenal crisis in patients with coexisting adrenal insufficiency 3, 5. This is particularly important in patients with autoimmune hypothyroidism, who have increased risk of concurrent autoimmune adrenal insufficiency (Addison's disease) 3.
For pregnant women or those planning pregnancy, any TSH elevation requires immediate treatment, as untreated hypothyroidism increases risk of preeclampsia, low birth weight, and neurodevelopmental effects in offspring 3, 6.
Common Pitfalls to Avoid
Overdiagnosis is common—many persons with mildly elevated TSH spontaneously revert to normal thyroid function without intervention 1. Approximately 37% of cases with mild TSH elevation normalize on their own 3.
Don't assume all elevated TSH represents permanent hypothyroidism—transient thyroiditis, recovery phase from severe illness, and medication effects can cause temporary TSH elevation 3. In up to 30% of infants and 10% of children with congenital hypothyroidism, TSH remains mildly elevated despite adequate treatment due to pituitary resistance that diminishes with age 4.
For patients already on levothyroxine with persistently elevated TSH, the most common cause is poor medication compliance 7. In compliant patients, consider malabsorption, drug interactions (particularly with calcium, iron, or proton pump inhibitors), or inadequate dosing 7.