Thrombin-antithrombin III complex (TAT) in plasma is a specific parameter for a latent activation of the clotting pathway. The concentration of the plasma TAT elevated in disseminated intravascular coagulation, deep vein thrombosis, pulmonary embolism, myocardial infarction, infectious diseases and malignant diseases. We serially monitored the plasma level of TAT in four collagen disease patients with active interstitial pneumonia. The degree of TAT in two patients who recovered from the interstitial pneumonia was decreased after the methylprednisolone pulse therapy. In contrast, the concentration of TAT in the two deceased patients was elevated. The concentration of plasma TAT may be a sensitive parameter for monitoring the disease activity of interstitial pneumonia in collagen diseases.
