Hemoglobin and hematocrit are equivalent in trauma patients

Results of hemoglobin (Hb) and hematocrit (Hct) measurement are routinely used to assess blood loss among trauma patients. But is it necessary to measure both parameters and if not, is one more reliable than the other? There is evidence to suggest that many physicians believe hematocrit is a more sensitive indicator of blood loss than hemoglobin. 

This study, conducted at a Level 1 trauma center in The Netherlands, was designed to establish if that belief is justified. Paired Hct and Hb levels were obtained from 671 severely injured patients of all ages during the first 7 days post injury. These included pretransfusion, during-transfusion and posttransfusion measurements; a total of 2461 paired data sets were available for statistical analysis. 

Both measurements were made using a Coulter Counter, on which Hb is determined by measuring absorption spectra of lyzed blood and Hct is computed from red-cell count and mean cell volume (MCV) measured by impedance. Mean Hb was 10.4 g/dL (interquartile range 8.7-12.1 g/dL) and mean Hct 30.9 % (interquartile range 25.8-35.8 %). 

Linear regression analysis revealed near-perfect correlation (Pearson’s R2 value of 0.99) between Hb and Hct, allowing the authors to conclude that Hb and Hct provide identical information in trauma patients. There is no rationale for the common practice of measuring both Hb and Hct, and Hct has no advantage over Hb for assessing blood loss in trauma patients. 

The derived regression coefficient (2.953) allowed construction of the following two equations for calculation of one parameter from the other:

Hct (%) = 2.953 × Hb (g/dL)
Hb (g/dL) = 0.334 × Hct (%)