To test the hypothesis that hypercoagulability after brain trauma was related to the severity of injury and also to outcome, new coagulation markers were used in 20 patients with isolated brain trauma. In addition to routine coagulation tests, soluble fibrin (SF), D-dimer, and antithrombin (AT) levels were assessed. Thirteen of 20 patients had a Glasgow coma score (GCS) of < or = 7 on admission and severe disability (SD) or worse on the Glasgow outcome scale (GOS). Eight patients had a very bad outcome [GOS = dead (D) or vegetative (V)]. All patients had increased SF levels (ref. < 15 nmol/L) at admission. Six patients with SF < 50 nmol/L had a good outcome with moderate disability (MD) or better. Patients with increasingly higher SF levels had a worse outcome: Three of five patients with SF 50 to 150 nmol/L were severely disabled (SD) or worse; four of six patients with SF > 150 nmol/L remained vegetative (V) or died (D). Four of the six patients with the highest D-dimer levels at admission remained vegetative (V) or died (D). Six of 13 patients with a significant drop in AT levels had a bad outcome (D or V) whereas only two of seven patients without AT consumption did poorly. Routine coagulation studies were often pathologic, i.e., reduced platelet count, but there was no relation to outcome. Increased SF and D-dimer levels at admission followed by a secondary decrease in AT concentration and platelets seem to be good markers of the posttraumatic hypercoagulation often seen after brain injury.(ABSTRACT TRUNCATED AT 250 WORDS)