| 摘要 |
In a double needle the blood withdrawal system the front needle for accomplishing the vena puncture is between 23 gauge and 29 gauge while the rear needle which resides in the syringe barrel and is used to puncture the stopper is similar to those standardly used between 12 and 16 gauge. The smaller gauge front needle acts as a flow restricter to prevent the initial blood sample drawn into the vacuum tube from impacting on the bottom wall of the tube thereby creating hemolysis of some of the red cells. The length of the front needle is between 0.5 and 1.5 inches.
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