the tourniquet during venipuncture. Both the
time of standing prior to venipuncture and the
time of tourniquet application should be kept to a
minimum.
2. Rapid flow of blood through small-bore needles
and exposures to large negative pressures lead to
hemolysis with its accompanying contamination
of the plasma portion of the blood specimen with
red cell cytoplasmic constituents. Hemolysis is
minimized by the use of large-bore needles,
moderate flow rates, and moderate negative
pressures. Invert specimen tubes gently to mix
the blood with additives.
3. Blood specimen contamination with intravenous
fluids is not uncommon. Blood should not be
drawn from a site above as intravenous infusion,
but must be obtained from a site on the patient's
other arm or, if necessary, below the infusion
site.
Medical Considerations
1. Local trauma from a venipuncture is usually
minimal. If bleeding into the soft tissues or
from the skin puncture site is noted during the
procedure, the tourniquet should be removed
immediately and direct pressure applied.
2. At the end of the venipuncture, direct pressure
should always be applied to the puncture site
until bleeding has ceased. This may take a long
time in patients who are anticoagulated or who
have a bleeding disorder.
3. Thrombosis and thrombophlebitis are rare
complications.
4. Some patients become faint during venipuncture.
The procedure should be terminated immediately
and the patient should lie flat until he or she
recovers.
Specimen Collection Procedures A-5
