The bleeding time in pediatrics.

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.