HUBUNGAN KADAR TIROGLOBULIN, TSH DAN fT4 SERUM PADA ANAK USIA SEKOLAH DI TIGA KABUPATEN DENGAN TINGKAT ENDEMISITAS DEFISIENSI-IODIUM BERBEDA (ASSOCIATION BETWEEN THE SERUM THYROGLOBULIN, TSH, AND fT4 AMONG SCHOOL-AGED CHILDREN IN THREE DISTRICTS WITH DIF