A tourniquet is used by the phlebotomist to assess and determine the location of a suitable vein for venipuncture. CLSI standards recommend single-use, latex-free tourniquets. Reusable tourniquets are no longer acceptable however, the use of a blood pressure cuff inflated below the patient's diastolic pressure in place of a tourniquet is still suitable if needed.
Proper application of a tourniquet will partially impede venous blood flow back toward the heart and cause the blood to temporarily pool in the vein so the vein is more prominent and the blood is more easily obtained. The tourniquet is applied three to four inches above the needle insertion point and should remain in place no longer than one minute to prevent hemoconcentration.
If the tourniquet is used during preliminary vein selection, it is best to release the tourniquet after assessing the vein and while you are assembling your supplies. Reapply the tourniquet just before starting the venipuncture; it should then be released soon after the needle has been inserted into the vein and the blood flows into the first tube. If collecting multiple tubes, the tourniquet may remain in place until blood enters subsequent tubes, however it needs to be removed within 1 minute from the moment it was applied.