The bleeding time in pediatrics

When performed with standardized methods and techniques, the bleeding time (BT) depends on variables that physiologically alter primary hemostasis. Th ese variables include number of platelets and platelet function, white and red blood cell counts, vascular factors, hormones, and temperature. Variati ons within normal limits reflect the in vivo situation and are of no clinic al relevance. If the BT is prolonged far above the upper normal limit, however, defects o f primary hemostasis have to be anticipated. These include thrombocytopenia or thrombocytopathy, anemia, leukopenia, and deficiencies of plasmatic fac tors such as von Willebrand factor (vWF), fibrinogen, the lupus anticoagula nt, and factor V. The BT can be used as screening test for patients with bl eeding symptoms. As a single test, the BT gives the best information in ped iatrics, in which defects of primary hemostasis are more common than coagul opathies. In addition, BT can guide the therapy of these patients, because it reflects clinical improvement. When used as a preoperative screening tes t, BT should be combined with the activated partial thromboplastin time (aP TT) because BT usually does not recognize patients with coagulopathies. With standardized techniques and the knowledge of its merits and limitation s, BT is a useful test for diagnosing hemostatic disorders, guiding their t herapy, 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 result s are immediately available; (4) it requires only minimal amounts of blood; and (5) it does not require unphysiological reagents and preparation of th e sample. The test requires a highly motivated and experienced operator who knows of the many variables influencing the BT. The interpretation cannot be done wi thout knowledge of the history and physical status of the patient and of th e limitations of the BT.