Did the blood work include an Activated Clotting Time (ACT) or other clotting profiles?
Causes of Nasal Bleeding
Sinus
Foreign bodies - such as foxtails, often with secondary infections
Fungal Infections
Tumors
Benign masses such as polyps
Bleeding disorders
Liver disease
Low platelets
Platelet dysfunction
Rodenticide poisoning
Other coagulation diseases
Common Diagnostics
General blood and urine testing
X-Rays (radiographs)
Coagulation blood tests
Fungal Blood Tests
Rhinoscopy and possible biopsy.
Hope that helps!