Anticoagulant-related bleeding: Given the patient is on Pradaxa (dabigatran), an anticoagulant, the most likely cause of gross hematuria is bleeding related to the anticoagulation therapy. Pradaxa works by inhibiting thrombin, which can increase the risk of bleeding, including urinary tract bleeding.

Urinary Tract Infection (UTI): UTIs are common in the elderly and can cause hematuria. The presence of an infection could be a contributing factor or a separate cause of hematuria.
Benign Prostatic Hyperplasia (BPH): Enlargement of the prostate is common in older men and can cause urinary retention, leading to bleeding.
Kidney Stones: While less common, kidney stones can cause severe pain and gross hematuria.

Bladder Cancer: Although less likely, bladder cancer is a critical diagnosis not to miss, as it can present with painless gross hematuria. The risk increases with age, and early detection is crucial for treatment.
Renal Cancer: Similar to bladder cancer, renal cancer can cause hematuria and is important not to miss due to its potential for severe outcomes if not treated early.
Sepsis from a urinary source: Infection leading to sepsis can be life-threatening and requires immediate attention. While not directly causing hematuria, it can be associated with urinary symptoms and is critical to identify.

Arteriovenous Malformation (AVM): AVMs in the urinary tract are rare and can cause bleeding. They are less likely but should be considered if other causes are ruled out.
Vasculitis: Certain types of vasculitis, such as IgA vasculitis, can affect the kidneys and cause hematuria. These conditions are rare and would typically present with other systemic symptoms.
Trauma: Although less likely in this context, any form of trauma (e.g., a fall) could cause hematuria, especially in an anticoagulated patient.