Residual Negative Pressure in Vacuum Tubes Might Increase the Risk of Spurious Hemolysis.

Background: We planned a study to establish whether spurious hemolysis may occur when negative pressure remains in vacuum tubes.

Methods: Four tubes with different vacuum levels (-54, -65, -74, and -86 kPa) were used to examine blood drawn from one healthy volunteer; the tubes were allowed to stand for different times (1, 2, 3, and 4 hours). The plasma was separated and immediately tested for free hemoglobin (FHb). Thirty patients were enrolled in a verification experiment.

Results: The degree of hemolysis observed was greater when the remaining negative pressure was higher. Significant differences were recorded in the verification experiment.

Conclusions: The results suggest that residual negative pressure might increase the risk of spurious hemolysis.