Prevalence of prolonged APTT and lupus anticoagulant in autoimmune thyroid disease

We describe prevalences of prolonged activated partial thromboplastin time(APTT) and lupus anticoagulant(LAC) in autoimmune thyroid disease(AITD). Prolonged APTTs were observed in 33(6.2%) blood samples out of 532 AITD cases(327 Graves' diseases and 205 Hashimoto's thyroiditis), but in only 8(2.0%) samples out of 396 non AITD cases(213 thyroid tumors, 14 subacute thyroiditis and 169 normal thyroids). The samples with prolonged APTT showed no abnormality in coagulation factors(factor VIII, IX, XI, XII, von Willebrand factor(vWF), prekallikrein, or high molecular weight kininogen) or factor VIII, IX inhibitor. Among samples with prolonged APTT, LAC evaluated by platelet neutralization procedure(PNP) was positive in 17(51.5%) samples of AITD, and in 2(25.0%) samples of non AITD. In prolonged APTT cases, the frequency of fetal loss in patients with AITD was higher than non AITD patients. But no significant difference was obtained between thyroid autoimmune antibody and the frequency of fatal loss. These indicate unknown biological association of between AITD and LAC.