Blood in Urine (Hematuria)

Hematuria is the medical term for the presence of blood in the urine. It can manifest in two distinct forms. Gross hematuria refers to blood that is visible to the naked eye, causing the urine to appear pink, red, or dark brown — sometimes resembling cola or tea. Microscopic hematuria refers to blood present in amounts too small to cause visible discoloration; it is detectable only through urinalysis under a microscope or by a dipstick urine test, and the urine appears completely normal in color.

While hematuria itself is a symptom rather than a diagnosis, it is one of the most important warning signs in urological medicine. It signals that bleeding is occurring somewhere within the urinary tract — which includes the kidneys, renal pelvis, ureters, urinary bladder, and urethra — and warrants thorough investigation regardless of whether it is painless or accompanied by other symptoms.

A critical clinical point is that the amount of visible blood does not reliably indicate the severity of the underlying condition. A very small tumor can produce striking gross hematuria, while a larger or more advanced lesion may cause only microscopic bleeding. Hematuria that is painless and intermittent — appearing one day and clearing the next — is particularly associated with urological malignancies and should never be attributed to benign causes without appropriate investigation.

Urological malignancies

• Blood in the urine is the most common presenting symptom of cancers affecting the urinary tract. The following malignancies most frequently cause hematuria:
  • Bladder cancer: The leading cancer cause of gross hematuria; typically painless and intermittent
  • Renal pelvis cancer and ureteral cancer (upper tract urothelial carcinoma): Hematuria is the initial symptom in the majority of patients with these cancers
  • Kidney cancer (renal cell carcinoma): Hematuria occurs in advanced or large tumors; when part of the classic triad (hematuria, flank pain, and abdominal mass), it usually indicates locally advanced disease
  • Prostate cancer: Can cause hematuria in advanced disease

Urinary tract infections (UTIs)

• Bacterial infections of the bladder (cystitis) or kidney (pyelonephritis) cause inflammation of the urothelial lining and frequently produce hematuria. UTI-related hematuria is typically accompanied by urinary frequency, urgency, dysuria (burning on urination), or fever, which helps distinguish it from malignancy-related hematuria.

Urinary tract stones (nephrolithiasis / urolithiasis)

• Kidney, ureteral, or bladder stones cause hematuria by traumatizing the urothelial lining as they move through the urinary tract. Stone-related hematuria is typically accompanied by severe, crampy flank or abdominal pain.

Benign prostatic hyperplasia (BPH)

• An enlarged prostate can cause hematuria through engorgement of surface blood vessels, particularly in men with significant prostatic enlargement.

Trauma

• Direct trauma to the kidneys, ureters, bladder, or urethra — from road traffic accidents, falls, pelvic fractures, or surgical procedures — can cause hematuria.

Vigorous exercise

• Sustained strenuous physical activity (e.g., long-distance running) can cause transient microscopic hematuria that resolves with rest. While not dangerous in itself, exercise-induced hematuria should be confirmed to have resolved fully and should not be assumed as the cause without excluding other etiologies.

Medications

• Anticoagulant therapy (warfarin, direct oral anticoagulants) can unmask or amplify hematuria from underlying pathology. The cyclophosphamide chemotherapy metabolite acrolein causes direct urothelial toxicity and hemorrhagic cystitis.

Risk factors for malignancy-related hematuria:

• Tobacco smoking (the most important risk factor for bladder and upper tract urothelial cancers)
• Age over 35–40
• Male sex
• Occupational exposure to aromatic amines, aniline dyes, or benzene compounds
• History of cyclophosphamide chemotherapy or pelvic radiation
• History of prior urological malignancy
• Aristolochic acid exposure
• Lynch syndrome

Any episode of gross hematuria (visible blood in the urine) in an adult requires prompt urological evaluation, regardless of whether it is accompanied by pain or other symptoms.

• Painless gross hematuria — even if it appears to resolve spontaneously — is the cardinal symptom of bladder cancer and upper tract urothelial carcinoma. Spontaneous resolution does not indicate that the underlying cause has resolved; it may simply reflect intermittent bleeding from a tumor.
• Microscopic hematuria detected on urinalysis should be confirmed on repeat testing and then evaluated by a urologist, particularly in adults over 35 and in those with any of the risk factors listed above.
• Hematuria accompanied by pain, fever, and urinary symptoms (frequency, urgency, dysuria) may suggest infection or stone disease, but cancer must still be excluded if hematuria persists after treatment of the identified cause.

Seek emergency evaluation immediately if:

• Gross hematuria is accompanied by the passage of large blood clots that appear to be causing urinary obstruction or inability to void
• Hematuria occurs in the context of significant abdominal or flank trauma
• Hematuria is accompanied by severe, sudden-onset flank or abdominal pain