Measurement of anti-thyroglobulin and anti-thyroid peroxidase antibodies using highly sensitive radioimmunoassay: an effective method for detecting asymptomatic focal lymphocytic thyroiditis in the elderly.

Subclinical thyroiditis or thyroid dysfunction is relatively common in the elderly. To estimate the effectiveness of measurement of serum levels of anti-thyroglobulin and anti-microsomal or thyroid peroxidase antibodies for detecting focal lymphocytic thyroiditis (FLT) in the elderly, we examined the relationships between antibody titer and postmortem histological finding of the thyroid gland in 180 consecutive autopsies (69 women and 111 men) over 60 years of age without any overt clinical thyroid or collagen diseases. FLT was found in 25 cases (13.9%) with female predominance (21.7% in female vs. 9.0% in male). Measurements of serum levels of anti-thyroglobulin and anti-thyroid peroxidase antibodies by radioimmunoassay (TgAb and TPOAb, respectively) were compared with the measurements of anti-thyroglobulin and anti-microsomal antibodies by a hemagglutination technique (TGHA and MCHA, respectively), using sera from 25 patients with FLT and age- and sex-matched 51 patients without FLT. Among 25 cases with FLT, TgAb and TPOAb were positive in 17 (68%) and 12 (48%), respectively. There was a close relationship between degree of FLT and serum level of TgAb or TPOAb (P<0.0001). On the other hand, TGHA and MCHA were positive only in 8 (32%) and 10 (40%), respectively. TgAb and TPOAb were more sensitive than TGHA (68% vs. 32%, P<0.05) and MCHA (48% vs. 40%) to detect FLT. Positive findings in either TgAb or TPOAb significantly improved sensitivity (76%) compared with that of TGHA or MCHA (44%) (P<0.05). Specificities of combined measurements of TgAb and TPOAb (90%) were not significantly different from those of TGHA and MCHA (100%). These findings indicate that TgAb is a more sensitive method for detecting FLT and that its diagnostic sensitivity for FLT increases by using it in combination with TPOAb. Therefore, in the elderly without clinically or biochemically overt thyroid dysfunction, positive TgAb and/or TPOAb could imply presence of FLT, and their titers might reflect degree of inflammation.