II. Approach
- TSH alone is sufficiently sensitive and specific
- TSH is a good single screening outpatient test
- Bauer (1996) Arch Intern Med 156:2333-7 [PubMed]
III. Interpretation: Normal Thyroid Stimulating Hormone (TSH): 0.3 to 5.0 mU/L
- Euthyroid
- No additional testing indicated
- Normal Serum TSH range is decreased in pregnancy
IV. Interpretation: High Thyroid Stimulating Hormone (TSH): >5-20 mU/L
- Normal Free Thyroxine Index or Free T4
- Diagnosis: Subclinical Hypothyroidism
- Non-specific Symptoms
- See Subclinical Hypothyroidism
- Consider Levothyroxine
- Goiter OR Microsomal Antibodies exceed 1:1600
- Positive: Levothyroxine
- Negative: Follow clinically
- Low Free Thyroxine Index or Free T4
- Diagnosis: Hypothyroidism
- Management: Levothyroxine
V. Interpretation: Low Thyroid Stimulating Hormone (TSH): <0.3 mU/L
- Normal Free Thyroxine Index or Free T4
- Normal Triiodothyronine (T3)
- Diagnosis: Subclinical Hyperthyroidism
- Management
- Consider following clinically
- Age over 60 years
- Risk of Atrial Fibrillation or Osteoporosis
- Consider definitive treatment
- Observe closely
- High Triiodothyronine (T3)
- Diagnosis: T3 Toxicosis
- Management: Treat Hyperthyroidism
- Normal Triiodothyronine (T3)
- High Free Thyroxine Index or Free T4
- Diagnosis: Hyperthyroidism
- Radioiodine Uptake scan Elevated:
- Grave's Disease
- Toxic nodular Goiter
- Toxic Thyroid Adenoma
- Radioiodine Uptake scan Low or Absent:
- Acute viral Thyroiditis
- Silent Thyroiditis
- Struma ovarii
- Excessive Levothyroxine ingestion