Objective Historically, perioperative hemoglobin monitoring has relied on calculated saturation, using blood gas devices that measure plasma hematocrit (Hct). Co-oximetry, which measures total hemoglobin (tHb), yields a more comprehensive assessment of hemodilution. The purpose of this study was to examine the association of tHb measurement by co-oximetry and Hct, using conductivity with red blood cell (RBC) transfusion, length of stay (LOS) and inpatient costs in patients having major cardiac surgery. Methods A retrospective study was conducted on patients who underwent coronary artery bypass graft (CABG) and/or valve replacement (VR) procedures from January 2014 to June 2016, using MedAssets discharge data. The patient population was sub-divided by the measurement modality (tHb and Hct), using detailed billing records and Current Procedural Terminology coding. Cost was calculated using hospital-specific cost-to-charge ratios. Multivariable logistic regression was performed to identify significant drivers of RBC transfusion and resource utilization. Results The study population included 18 169 cardiovascular surgery patients. Hct-monitored patients accounted for 66% of the population and were more likely to have dual CABG and VR procedures (10.4% vs. 8.9%, P=0.006 9). After controlling for patient and hospital characteristics, as well as patient comorbidities, Hct-monitored patients had significantly higher RBC transfusion risk (OR=1.26, 95%CI 1.15-1.38,P<0.000 1), longer LOS (IRR=1.08, P<0.000 1) and higher costs (IRR=1.15, P<0.000 1) than tHb-monitored patients. RBC transfusions were a significant driver of LOS (IRR=1.25, P<0.000 1) and cost (IRR=1.22, P<0.000 1). Conclusion tHb monitoring during cardiovascular surgery could offer a significant reduction in RBC transfusion, length of stay and hospital cost compared to Hct monitoring.