Screening for Subclinical Autoimmune Thyroid Diseases with Highly Sensitive Assays for Autoantibodies to Thyroglobulin and Thyroid Peroxidase and Serum Thyrotropin Concentrations

The prevalence of subclinical autoimmune thyroid diseases (AITD) was investigated with determinations of highly sensitive anti-thyroid peroxidase antibody (TPOAb), anti-thyroglobulin antibody (TgAb) and thyroid stimulating hormone (TSH) in serum samples obtained from 2,647 ostensibly healthy subjects (1,887 males and 760 females, aged 46.0±10.4 years, Mean±SD) residing in Sapporo who were recruited at the hospital for medical examinations. The prevalence of thyroid autoantibodies (TAA) was 9.1% (n=242), among which 23.6% was TgAb positive only (>1.83 U/ml), while 46.3% was TPOAb positive only (>0.34 U/ml), and the remaining 32.2% were both TPOAb and TgAb positive. TAA was positive in 6.5% for males and 15.8% for females (P<0.001) with an age-related increase. The prevalence of subclinical hyperthyroidism (TSH<0.15 mU/L) was 0.79%, of which 42.1% was positive for TAA. The prevalence of subclinical hypothyroidism (TSH>5.0 mU/L) was 1.1%, of which 20% were TAA positive. The overall prevalence of subclinical autoimmune thyroiditis as defined by TAA positive eu- and hypothyroidism was 8.8%; 6.3% for males and 15.5% for females (P<0.001). There was a significant inverse correlation between TPOAb and TSH levels (r=-0.21, P<0.05, n=112) in subjects with TPOAb positive only and also a significant correlation between TgAb and TSH levels in subjects with positive TgAb with or without TPOAb (r=0.27, P<0.01, n=130). This study indicates that the combined analysis of TPOAb, TgAb and TSH may provide more accurate information on the prevalence of AITD in the population study.