Letter to the Editor Re: Serum Calprotectin in Adolescents WithInflammatory Bowel DiseaseT o the Editor: We were interested to read the article by Carlsen et al (1) describing their evaluation of serum calprotectin (SC) in children with inflammatory bowel disease (IBD). Initially SC correlated with serum C-reactive protein (CRP) and endoscopic severity but not with fecal calprotectin (FC) in 19 adolescents with ulcerative colitis (UC). SC was then measured in longitudinally collected samples: SC correlated with FC in the children with UC in this cohort, but not those with Crohn disease.Previous work demonstrated higher levels of SC in 31 children with IBD than in children without IBD (2). FC was not measured. SC correlated with CRP. On reanalysis of the previous data, however, SC did not correlate with mucosal calprotectin (MC) (Spearman r ¼ 0.27, P ¼ 0.14).Although FC has high sensitivity and specificity in identifying IBD in children presenting with gastrointestinal symptoms (3), it may not always reflect mucosal healing (4) or the extent of ileal disease (5). Furthermore, some patients prefer a blood test over collecting a stool sample. Consequently, a serum marker would certainly have a role in IBD. Standard markers provide variable indications of disease activity (6,7). SC has high test utility in conditions such as juvenile arthritis (8), but does not appear to have the same benefits in IBD.Overall, these evaluations show that SC was raised in children with IBD, but correlated inconsistently with FC or MC (1,2). Although SC correlated closely with CRP, it may not offer advantages over CRP. The role of SC in children with IBD remains unclear.