- Thrombocytopenia is the most common hematological abnormality associated with petechiae and purpura, due to a reduced platelet count leading to impaired primary hemostasis.
- Platelets play a crucial role in forming the initial platelet plug at sites of vascular injury.
- When platelet numbers fall below a critical threshold, small vessel bleeding manifests as petechiae (pinpoint hemorrhages) and larger purpuric lesions in the skin and mucous membranes.
- In contrast, leukocytosis, polycythemia vera, and hemophilia A primarily affect other aspects of the blood or coagulation but do not predominantly cause these specific bleeding manifestations.

Reference: Davidson’s Principles and Practice of Medicine, 23rd Edition, Chapter: Disorders of the Blood, Page 547.