Monitoring of thiopurine levels among patients with inflammatory bowel disease (IBD) can be costly and burdensome. Precise target levels are not clear and may vary among patients depending on individual metabolism. A more readily available and economical laboratory marker of disease activity among pediatric patients with IBD treated with thiopurines is needed. In this study, we aim to determine if a ratio of mean corpuscular volume (MCV) to white blood cell count (WBC) >12 is associated with clinical disease activity among a pediatric and young adult IBD population.Methods:
A retrospective chart review of 234 clinical encounters among 43 patients with IBD treated with thiopurines was performed. Clinical encounters were included in analysis if laboratory testing including a complete blood count (CBC) were collected at the time of a clinic visit from which a clinical disease activity score could be calculated. Additional information including months on thiopurine treatment, additional medications, inflammatory markers, and thiopurine metabolite levels were obtained when available.Results:
We found that a ratio of MCV to WBC > 12 is associated with clinical response among patients with ulcerative colitis as measured by a Pediatric Ulcerative Colitis Activity Index (PUCAI) score less than or equal to 10 (OR 4.72, P = 0.004) and among patients with IBD as measured by a Physician Global Assessment (PGA) of inactive disease (OR 5.21, P < 0.001). There was no association between MCV to WBC ratio >12 and Crohn's disease activity as measure by the abbreviated Pediatric Crohn's Disease Activity Index (aPCDAI). There was also no association between 6-thioguanine nucleotide metabolite levels and clinical response as measured by PUCAI, aPCDAI, or PGA.Conclusions:
Though future studies are needed with a larger pediatric study population, the ratio of MCV to WBC >12 appears to be a practical and cost-effective surrogate of disease activity among pediatric patients with IBD treated with thiopurines.