BLEEDING-TIME AT ALTITUDE

Disorders of coagulation during ascent to high altitude in the unaccli matized are well recognized. In order to document the sequence of haem atological changes, the bleeding time was estimated weekly in six clim bers during a six week climb. The median bleeding time was shown to in crease by 50% between the first and fourth week, it then plateaued dur ing continued ascent to 5700 m. During the sixth week the bleeding tim e rapidly reverted to baseline levels whilst still at altitude. The ob servations might be explained by the compensatory changes in coagulati on factors following the initial prothrombotic phase, compounded by in creased capillary fragility. Acclimatization to altitude is accompanie d by a series of complex haematological changes. The temporal sequence should be considered when devising a strategy to reduce the risk of t hrombosis.