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Literature on Hypothyroidism

Implications for the Diagnosis of Subclinical Hypothyroidism

Thomas E. Hamilton, Scott Davis,et. al.,

J Clin Endocrinol Metab. 93(4):1224–1230, April 2008

Programs in Epidemiology (T.E.H., S.D., L.O.) and Cancer Prevention (K.J.K.), Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109; Division of Endocrinology and Metabolism (T.E.H.), University of Washington School of Medicine, Seattle, Washington 98195; and Departments of Epidemiology (S.D.) and Biostatistics (K.J.K.), University of Washington School of Public Health and Community Medicine, Seattle, Washington 98195

Context: The current debate regarding whether to decrease the upper limit for the TSH reference range to 2.5 μIU/ml has considerable potential impact on the diagnosis and treatment of subclinical hypothyroidism worldwide.

Objective: We report an analysis of TSH distribution in a population with no evidence of thyroid disease, including a normal thyroid ultrasound.

Design: A subset of the Hanford Thyroid Disease Study cohort was used to examine the TSH distribution in a population having no evidence of thyroid disease, seronegative thyroid autoan- tibodies, no history of thyroid medications, and a normal thyroid ultrasound. The shape of the TSH distribution was compared with the Gaussian and lognormal distributions.

Setting: This study was performed in the general community. Participants: Of 1861 Hanford Thyroid Disease Study participants with TSH measured by ELISA who also had thyroid peroxidase antibody measurements, 766 comprised the normal reference group 3 (NRG-3) with no evidence of thyroid disease, including no positive antibodies and normal thyroid ultrasound.

Main Outcome Measure: TSH was measured.

Results: The TSH distribution in the NRG (NRG-3) was right skewed and followed an approximate lognormal distribution. The best estimates of the 97.5th percentile, the percentage above 2.5 μIU/ml, and the percentage above 3.0 μIU/ml for TSH by 3rd generation immunochemilumino- metric assay are 4.1 μIU/ml, 20% and 10.2%, respectively.

Conclusion: These results indicate that the TSH reference range should be narrowed and support a value of approximately 4.0 as the upper-reference limit. (J Clin Endocrinol Metab 93: 1224 –1230, 2008)