Does intravenous NAC affect coagulation tests?
It does in a way that it is very important for clinicians to understand. In a study of 87 patients with APAP toxicity, Schmidt et al (Lancet 2002;360:1151) found that even in the absence of hepatocellular injury, IV NAC decreased prothrombin index by an average of approximately 33 percent. (The literature on this subject is somewhat confusing until one realizes that a decrease in prothrombin index corresponds to an increase in prothrombin time.) The reason for this change is not completely clear, but may involve a direct action of NAC on several vitamin-K-dependent clotting factors (especially factor VII), destabilizing their protein structure and inhibiting their activity. Physicians must be aware that an isolated elevation of the prothrombin time in patients treated with IV-NAC does not necessarily indicate liver injury, especially when determining prognosis and indication for referral to a liver transplant service. There is no evidence that this effect on the prothrombin time causes
