Antithyroid peroxidase antibodies in patients with high normal range thyroid stimulating hormone

Hypothyroidism is linked to heart disease and decreased quality of life. Since screening guidelines for the general population are controversial, and physicians use clinical judgment in deciding to order thyroid stimulating hormone (TSH), high-normal levels of TSH pose a dilemma. This study's objective was to compare rates of positive anti-thyroid peroxidase antibodies (antiTPO) tests in persons with high-normal versus low-normal TSH levels.

Physicians at a publicly funded family medicine outpatient clinic used a standard clinical set of criteria to identify patients in need of TSH testing. Patients with non-thyroid diseases or conditions that affect TSH were excluded. A total of 143 patients over 18 years of age presented with symptoms necessitating TSH testing and had levels that fell between 0.36 and 5.49 IU/ml. They were allocated into two groups: 100 patients with TSH levels between 0.36--2.49 IU/ml (low-normal TSH ) and 43 patients with TSH levels between 2.5--5.49 IU/ml (high-normal TSH ), and they all had measurements of antiTPO levels. Primary outcomes were rates of antiTPO and demographics comparisons between the two groups.

The prevalence of the antiTPO antibody in the high-normal group was 18.6% versus 3% in the low-normal range TSH. The antiTPO prevalence was higher in females than in males and had a racial predominance in Hispanics compared to African Americans; however, these differences were not statistically significant.

AntiTPO measurement may be appropriate for patients with high-normal TSH to help distinguish those at risk of developing true hypothyroidism.