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J Pediatr Gastroenterol Nutr. 2019 Feb 7. doi: 10.1097/MPG.0000000000002296. [Epub ahead of print]

Mean Corpuscular Volume to White Blood Cell Ratio for Thiopurine Monitoring in Pediatric Inflammatory Bowel Disease.

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Division of Pediatric Gastroenterology, Ann Arbor, MI.
Children's Health Evaluation and Research Center, University of Michigan, Ann Arbor, MI.
School of Public Health, University of Michigan, Ann Arbor, MI.
VA Center for Clinical Management Research, VA Ann Arbor Health Care System, Ann Arbor, MI.
Division of Gastroenterology and Hepatology, University of Michigan Health System, Ann Arbor, MI.



Thiopurines, commonly used to treat inflammatory bowel disease (IBD), cause lymphopenia and red blood cell macrocytosis, requiring therapeutic monitoring. Mean corpuscular volume/white blood cell (MCV/WBC) ratio has been proposed as a surrogate for therapeutic monitoring. Our aim was to investigate MCV/WBC ratio for assessing clinical response to thiopurines among pediatric IBD patients.


We performed a retrospective cross-sectional study at a tertiary care center using laboratory results and standardized physician global assessments (PGA) among pediatric patients taking thiopurines. Erythrocyte sedimentation rate (ESR), c-reactive protein (CRP), fecal calprotectin, and 6-thioguanine nucleotides were assessed when available. The primary outcome was association between MCV/WBC ratio and clinical remission assessed by ESR, CRP, calprotectin, or PGA. We also used a composite outcome requiring all available data to be normal. Analyses were limited to one occurrence per patient, >60 days after starting thiopurine, and comparators were required to be within 14 days of one another.


471 patients met inclusion criteria. MCV/WBC ratio poorly predicted quiescent disease as defined by PGA (area under receiver operating characteristic curve [AuROC] 0.55, 95% confidence interval [CI] 0.43-0.66). MCV/WBC ratio better predicted quiescent disease defined as normal CRP (AuROC 0.64, 95% CI 0.58-0.70) or normal ESR (AuROC 0.59, 95% CI 0.52-0.66). When the composite outcome measure was used, MCV/WBC ratio had an AuROC of 0.65 (95% CI 0.59- 0.70), indicating it is reasonably accurate in discriminating between clinical remission and active disease.


MCV/WBC ratio is a non-inferior, easy, and low-cost alternative to thiopurine metabolite monitoring.

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