TSH reference values for adult Brazilian population

Area of Science:

• Endocrinology
• Clinical Biochemistry
• Population Health

Background:

• Thyroid-stimulating hormone (TSH) is a key indicator of thyroid function.
• Establishing population-specific normal ranges is crucial for accurate diagnosis.
• Previous TSH reference ranges may not accurately reflect the Brazilian adult population.

Purpose of the Study:

• To define the normal serum TSH reference range for Brazilian adults (18-60 years).
• To align with National Academy of Clinical Biochemistry guidelines.
• To provide a basis for improved thyroid disorder diagnosis in Brazil.

Main Methods:

• Healthy Brazilian volunteers (n=960) were recruited, excluding individuals with thyroid disease, relevant medical history, or medication use.
• Exclusion criteria included anti-thyroid peroxidase antibodies and abnormal free T4 levels.
• Serum TSH levels were measured to determine the 2.5th and 97.5th percentiles.

Main Results:

• The 2.5th percentile TSH value was 0.43 mIU/L.
• The 97.5th percentile TSH value was 3.24 mIU/L.
• 9.15% of volunteers had TSH > 2.5 mIU/L, and 3.11% had TSH > 3 mIU/L.

Conclusions:

• The study suggests an upper limit of normal serum TSH for Brazilian adults is approximately 3.5 mIU/L.
• This finding may refine diagnostic criteria for thyroid dysfunction in this population.
• Further research can validate these reference intervals across diverse Brazilian demographics.