An 18-year-old woman comes to the clinic due to recurrent blood in her urine over the past month, which she experienced again this morning. The patient has had no recent injuries, infections, fever, dysuria, urinary frequency, or pain. She has no chronic medical conditions and takes no medication. The patient is sexually active with a male partner and uses condoms for contraception. She follows a vegan diet and has recently started training for a triathlon by bike riding and long-distance running. Temperature is 36.9 C (98.4 F), blood pressure is 110/78 mm Hg, pulse is 76/min, and respirations are 14/min. Examination shows no mucosal pallor. Cardiopulmonary examination is normal. Abdomen is soft and nontender. There is no skin rash. Laboratory results are as follows:
| Serum chemistry | |
| Blood urea nitrogen | 14 mg/dL |
| Creatinine | 0.8 mg/dL |
| Creatine kinase | 60 U/L (normal 10-90 U/L) |
| Urinalysis | |
| Specific gravity | 1.0219 |
| Protein | none |
| Blood | 3+ |
| Leukocyte esterase | negative |
| Bacteria | none |
| White blood cells | 1-2/hpf |
| Red blood cells | 50+/hpf |
| Casts | none |
| Crystals | none |
What is the most likely cause of this patient's presentation?
Show Explanatory Sources
Significant exertion (eg, long-distance running) can lead to dark urine due to the following:
Because urinary RBCs are absent with myoglobinuria and hemoglobinuria, the presence of ≥3 RBC/hpf on this patient's urinalysis makes her most likely diagnosis benign exercise-induced hematuria due to traumatic injury to the bladder mucosa. In addition, her normal creatine kinase level is inconsistent with rhabdomyolysis (Choice C).
Long-distance runners and cyclists are at highest risk for exercise-induced hematuria because repeated collision of the bladder wall and base while running, or the bladder and the perineum during a bumpy bike ride, leads to bruising and bleeding of the mucosal lining. Further testing is not typically required for diagnosis in a patient with a classic history and no other findings concerning for renal disease (eg, hypertension, proteinuria, elevated creatinine). Symptoms are generally self-limited, with resolution of hematuria expected within a week of discontinuing the triggering exercise.
(Choice A) Urinary tract infection, or bacterial invasion of the urogenital epithelium, typically presents with dysuria, urgency, and frequency, none of which are seen in this patient. Hematuria can occur, but urinalysis would also show bacteria, leukocyte esterase, and/or white blood cells.
(Choice B) Lupus nephritis (associated with anti-dsDNA) most commonly presents with proteinuria but can present with microscopic hematuria. However, creatinine is typically elevated, and urinalysis often shows RBC casts due to glomerular disease, which are not seen in this patient.
(Choice D) Malignant transformation of urothelium (ie, bladder cancer) can cause painless hematuria but typically presents in older men (age >55) exposed to cigarette smoke. This woman's age makes this diagnosis very unlikely.
Educational objective:
Exercise-induced hematuria is a benign condition that can occur in long-distance runners due to traumatic injury to the bladder mucosa from repeated collision of the bladder wall and base. The presence of urinary red blood cells distinguishes this condition from exertional skeletal muscle injury causing myoglobinuria.