We thank Dr Card for his comments on our recent paper ‘C-reactive protein, an indicator for maintained response or remission to infliximab in patients with Crohn's disease’.[1, 2] The primary objective of our post hoc analysis from ACCENT I was to assess the relationship between the serum CRP levels at week 14 and maintenance of response and remission from weeks 14 to 54 in patients with response and remission, respectively, to induction treatment with infliximab.
The key message of our results is that patients whose CRP had normalised to <0.5 mg/dL by week 14 from a baseline level above this value had a PPV to maintain response and remission of 90.5% and 75%, respectively, until week 22, i.e. the next infusion interval. The corresponding PPVs decreased with time from week 14. Conversely, the negative predictive value of CRP levels above normal at week 14 was low to predict a short term loss-of-response to infliximab therapy, but increased steadily with time, but not exceeding 68%.
These findings underscore the short half-life time of CRP and indicate that CRP measurements need to be performed repetitively before infliximab infusions to utilize its high PPV for predicting maintenance of response or remission. It remains to be determined how infliximab trough levels might add value to CRP as predictor of relapse in ACCENT I.