Users beware! Biological variation in complete blood counts over short time intervals.

Competing Interests: Competing interests: Johns Hopkins University holds a Board of Directors position in miDiagnostics, owns equity in the company and is also eligible to receive royalty payments for commercial sales by miDiagnostics. AD, JB, RB, SR and YM are eligible to receive distributions of royalty payments to JHU and/or payments related to JHU equity ownership interests in miDiagnostics. This arrangement has been reviewed and approved by the Johns Hopkins University in accordance with its conflict of interest policies.