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Thyroid Function Test

General
1. TSH alone is sufficiently sensitive and specific
2. TSH is a good single screening outpatient test
3. References
  1. Bauer (1996) Arch Intern Med 156:2333
Normal Thyroid Stimulating Hormone (TSH): 0.3 to 5.0 mU/L
1. Normal Free Thyroxine Index or Free T4
  1. Diagnosis: Euthyroid
2. Low Free Thyroxine Index or Free T4
  1. Diagnosis: Secondary Hypothyroidism (Central)
High Thyroid Stimulating Hormone (TSH): >5-20 mU/L
1. Normal Free Thyroxine Index or Free T4
  1. Diagnosis: Subclinical Hypothyroidism
  2. Management
    1. Non-specific Symptoms: Consider Levothyroxine
    2. Goiter OR Microsomal Antibodies exceed 1:1600
      1. Positive: Levothyroxine
      2. Negative: Follow clinically
2. Low Free Thyroxine Index or Free T4
  1. Diagnosis: Hypothyroidism
  2. Management: Levothyroxine
Low Thyroid Stimulating Hormone (TSH): <0.3 mU/L
1. Normal Free Thyroxine Index or Free T4
  1. Normal Triiodothyronine (T3)
    1. Diagnosis: Subclinical Hyperthyroidism
    2. Management
      1. Consider following clinically
      2. Age over 60 years
        
        Risk of Atrial Fibrillation or Osteoporosis
        
        Consider definitive treatment
        
        Observe closely
  2. High Triiodothyronine (T3)
    1. Diagnosis: T3 Toxicosis
    2. Management: Treat Hyperthyroidism
2. High Free Thyroxine Index or Free T4
  1. Diagnosis: Hyperthyroidism
  2. Radioiodine Uptake scan Elevated:
    1. Grave's Disease
    2. Toxic nodular Goiter
    3. Toxic Thyroid Adenoma
  3. Radioiodine Uptake scan Low or Absent:
    1. Acute viral Thyroiditis
    2. Silent Thyroiditis
    3. Struma ovarii
    4. Excessive Levothyroxine ingestion
References
1. Costa (1995) Am Fam Physician 52(8):2325
2. Pittman (1996) Am Fam Physician 54(3):961

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This page was written by Scott Moses, MD. This page was last revised before 5/10/08, prior to consistent tracking of revision date. This page was last published on 5/16/2008. Please send comments and questions to the editor. Contact information may be found on the page About the Family Practice Notebook. These pages are best viewed with Microsoft Internet Explorer 6.0.