A comparison of conductivity-based hematocrit determinations with conventional laboratory methods in autologous blood transfusions.

An investigation was made of the accuracy of a portable hematocrit measurement device (Stat-Crit) on the infusate of an autologous blood transfusion system. Baseline hematocrit values were determined by three methods on in vivo blood samples of surgical patients immediately after the start of surgery, and again on the first product of the autologous blood retrieval system. At baseline, there were no significant differences in the values determined by the Stat-Crit (33.4% +/- 6.2%, mean +/- SD) and those determined by the microcentrifuge technique (33.8% +/- 4.7%) or by the Coulter method (33.5% +/- 4.5%) (P = 0.9). In contrast, hematocrit values determined on infusate samples by the Stat-Crit (36.6% +/- 4.8%) were significantly lower than those determined by the microcentrifuge technique (51.2% +/- 5.9%) or by the Coulter method (51.6% +/- 5.8%) (P = 0.0001). This study confirms close agreement of hematocrit values derived by the conductivity of whole blood in normal samples with those determined by conventional laboratory techniques, but indicates that this method will report falsely low readings in situations where plasma has been replaced by crystalloid, as in patients who have received large transfusions of processed autologous blood.