Abstract
When performed with standardized methods and techniques, the bleeding time (BT) depends
on variables that physiologically alter primary hemostasis. These variables include
number of platelets and platelet function, white and red blood cell counts, vascular
factors, hormones, and temperature. Variations within normal limits reflect the in
vivo situation and are of no clinical relevance.
If the BT is prolonged far above the upper normal limit, however, defects of primary
hemostasis have to be anticipated. These include thrombocytopenia or thrombocytopathy,
anemia, leukopenia, and deficiencies of plasmatic factors such as von Willebrand factor
(vWF), fibrinogen, the lupus anticoagulant, and factor V. The BT can be used as screening
test for patients with bleeding symptoms. As a single test, the BT gives the best
information in pediatrics, in which defects of primary hemostasis are more common
than coagulopathies. In addition, BT can guide the therapy of these patients, because
it reflects clinical improvement. When used as a preoperative screening test, BT should
be combined with the activated partial thromboplastin time (aPTT) because BT usually
does not recognize patients with coagulopathies.
With standardized techniques and the knowledge of its merits and limitations, BT is
a useful test for diagnosing hemostatic disorders, guiding their therapy, and warning
of unexpected bleeding complications during surgery.
The BT is especially suited for use in pediatrics for the following reasons: (1) It
does not require a venipuncture and is similar to capillary blood sampling if performed
with standardized devices adapted for pediatric use; (2) it is an in vivo test informing
mostly on defects of primary hemostasis, which are the most common bleeding diatheses
in childhood; (3) the results are immediately available; (4) it requires only minimal
amounts of blood; and (5) it does not require unphysiological reagents and preparation
of the sample.
The test requires a highly motivated and experienced operator who knows of the many
variables influencing the BT. The interpretation cannot be done without knowledge
of the history and physical status of the patient and of the limitations of the BT.
Keywords:
Bleeding time - primary hemostasis - children - preoperative screening - thrombocytopathy
- monitoring of therapy
