The acute phase reaction explains only a part of initially elevated factor VIII:C levels: a prospective cohort study in patients with venous thrombosis.

We determined in a prospective cohort of patients treated with vitamin K antagonists for venous thrombosis, the course of factor VIII (FVIII:C), C-reactive protein (CRP) and fibrinogen levels, to assess the influence of the acute phase reaction on FVIII:C levels. Second, we hypothesized that patients with preceding infectious symptoms might have higher levels of FVIII:C at baseline than patients without those. We included 75 patients. Blood was sampled at baseline, once during treatment (t=1) and at the end of treatment (t=2). Mean levels of FVIII:C were 207, 186 and 175IU/dL (p for trend 0.003) at baseline, t=1 and t=2 respectively. Eight-eight percent of patients had an elevated FVIII:C at baseline, 75% at t=1 and 72% at t=2 (p for trend 0.045). Mean levels of FVIII:C were not different in patients with or without preceding infectious symptoms (206 versus 205IU/dL respectively). A baseline CRP level below 62mg/L could best distinguish between patients who will keep an elevated FVIII:C and those who will drop below 150IU/dL. We conclude that FVIII:C levels are partially influenced by the acute phase reaction, especially in patients who keep a persistent elevated FVIII:C during treatment. Preceding infectious symptoms did not influence baseline FVIII:C levels.