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Primary care
Users beware! Biological variation in complete blood counts over short time intervals
  1. Andrea DeLuca1,
  2. Joshua Betz2,
  3. Robert Bollinger3,
  4. Stuart Ray3,
  5. Yukari Manabe3
  1. 1 Department of Health Policy and Management, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, USA
  2. 2 Department of Biostatistics, Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, USA
  3. 3 Johns Hopkins School of Medicine, Baltimore, Maryland, USA
  1. Correspondence to Andrea DeLuca, Johns Hopkins University Bloomberg School of Public Health, Baltimore, MD 21231, USA; adeluca{at}

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A complete blood count (CBC) is the most commonly ordered laboratory test for patient diagnosis and treatment.1 Clinical decisions are often made on the basis of a single result which is rarely repeated. The availability of more rapid tests for CBCs that are accessible and approved for Clinical Laboratory Improvement Amendments (CLIA)-waived use at the point of need increases the likelihood that serial testing may occur over short periods of time.2 Understanding natural CBC variation in healthy individuals may help clinicians interpret serial test results which may have a range of values.


We sought to evaluate CBCs from blood drawn over a short time period and assessed in separate, accredited labs to understand biological and laboratory-based variability.

Methods and findings

Ten healthy adult volunteers with a self-report of being healthy were recruited by a study nurse and signed informed consent between April and May 2017. At baseline, 1 hour and 2 hours, six 3 mL tubes were drawn each time and sent as routine tests in duplicate to three College of American Pathologist certified clinical core laboratories for CBC: Lab 1 used a Beckman Coulter LH750 (Beckman Coulter, Atlanta, GA), Lab 2 used a Sysmex XE2100 (Sysmex America, Lincolnshire, IL) and Lab 3 used a Sysmex XN9000 (Sysmex America). The total time range covered by this study was 120 min, consistent …

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