Purpose: Perioperative fluid therapy is used to optimize tissue perfusion. Existing methods to quantify blood volume and estimate intravenous (IV) fluid requirements are either inaccurate or require specialized equipment and training. This study assessed the utility of mild hemodilution for quantifying blood volume. Design: A prospective validation design was used. Blood volume was quantified utilizing two methods in a fixed order: radiodilution, then hemodilution as described in D' Angelo et al. (2014). Methods: After IRB approval and informed consent, blood volume (BV) estimates were derived for each subject using radiodilution via the Daxor BVA-100, and from pre- and post-bolus hematocrit (HcT) using methods described in D'Angelo, et al. (2014). Hematocrit was assessed via 3 methods: Microimpedence via an i-STAT device and the Duke University Medical Center Lab, and total hemoglobin (SpHb, Masimo Corporation, Irvine, CA) . Sample: Thirty-three healthy, male subjects aged 18-35 years. Analysis: Bland-Altman plots, the intraclass correlation, and Lin's Concordance Coefficient were utilized to compare the gold standard of radiodilution and the proposed method of mild hemodilution for each method of measuring HcT (i-STAT, Lab, and SpHb). Findings: Mean BV estimates were 5568.6902.2 ml via radiodilution, 8521.23526.5 ml via i-STAT, 16411.013774.5 via Duke lab, and 15882.022371.0 via the Masimo SpHb device. Agreement in estimated BV between methods was low (Lin's Concordance Coefficient 0.02-0.05). Crystalloid loss to extravasation or renal filtration necessary to account for the observed differences between methods ranged from 181.9 ml to 299.7 ml over 6 minutes.