What laboratories should do
Back to Feature Story
So what should laboratories do about the preanalytical variability
of partial-draw sodium citrate coagulation tubes? According to Becton
Dickinson, laboratories should stop using the partial-draw tubes
immediately for monitoring activated partial thromboplastin time
in patients receiving unfractionated heparin and for conducting
But, as BD vice president for medical affairs Jeffry Lawrence,
MD, acknowledged, heparin monitoring represents probably less than
five percent of all the tests performed with coagulation tubes.
Partial-draw tubes are entirely suitable for other forms of testing,
including determining prothrombin time or coagulation testing of
patients who have long APTTs unrelated to unfractionated heparin,
such as those with hemophilia or von Willebrand’s disease.
"For the time being, while laboratories are transitioning to a
different product, they should have no problem using the partial-draw
tubes to generate prothrombin times or APTTs for other patient populations,"
However, laboratories will need to regroup when BD pulls the partial-draw
tubes off its assembly line on Sept. 30. The best answer for most
laboratories is to return to the full-draw sodium citrate tube.
"This, after all, is the tube that’s been used to generate all the
clinical recommendations, and it is considered to be the gold standard
around the world for coagulation testing," Dr. Lawrence says. The
full-draw tube’s traditional 13 ¥ 17 mm configuration is compatible
with holders, centrifuges, and coagulation analyzers.
Laboratorians and physicians who want to avoid preanalytical variability
and still draw lower volumes of blood have other alternatives. Pediatric
tubes that draw either 2.7 mL or 1.8 mL of blood have a different
configuration than that of the partial-draw tubes and, consequently,
do not cause platelet activation. Because these tubes are smaller
than standard coagulation tubes, however, they may not be compatible
with laboratory instrumentation.
The CTAD tube has been available in Europe for a few years and
is being released now in the U.S. It is a full-size, 13 ¥ 75 mm
tube that is under-evacuated to draw 2.7 mL of blood. Because of
its platelet-inhibiting cocktail of theophylline, adenosine, and
dipyridamole, the tube does not interfere with unfractionated heparin
monitoring or platelet counting, Dr. Lawrence says. This additive-specifically
dipyridamole-is light-sensitive, so there are special handling requirements
When a laboratory switches to one of these alternatives, it should
establish a new reference range, just as it would when adding another
instrument or a different reagent. "The laboratory would need to
determine the reference range for a healthy population and follow
the CAP recommendations for establishing its heparin therapeutic
range, using the Brill Edwards or some other method described by
CAP," Dr. Lawrence says.