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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.

Author information

1
Division of Pediatric Gastroenterology, Ann Arbor, MI.
2
Children's Health Evaluation and Research Center, University of Michigan, Ann Arbor, MI.
3
School of Public Health, University of Michigan, Ann Arbor, MI.
4
VA Center for Clinical Management Research, VA Ann Arbor Health Care System, Ann Arbor, MI.
5
Division of Gastroenterology and Hepatology, University of Michigan Health System, Ann Arbor, MI.

Abstract

OBJECTIVES:

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.

METHODS:

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.

RESULTS:

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.

CONCLUSIONS:

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

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