It is quite obvious to almost everyone that blood in urine is not a normal finding. Therefore, it is easy to understand why so many people become alarmed when it happens.

In general, a reddish or darkened urine indicates that something is wrong with the genitourinary system, although not all cases are caused by serious medical conditions. Actually, most of them aren’t.

Blood in urine, known medically as hematuria, is not always visible to the naked eye. In some cases, the amount of red blood cells in the urine is so small, that it can only be detected under a microscope, through urinalysis.

In most circumstances, hematuria is caused by an urinary tract infection. However, a wide range of diseases can cause blood in urine, from serious illness, such as bladder or kidney cancer, to harmless conditions, such as some mild genetic defects in the renal tubules.

What is hematuria?

The simplest definition of hematuria is the presence of blood in urine.

In most situations, the patient with hematuria does not have a frankly bloody urine with visible clots. As a matter of fact, in most cases of hematuria, the urine looks quite normal. The blood loss in urine can be so small, that it is not possible to notice its presence just by looking at it.

On the other hand, not all reddish urine are due to blood loss. The presence of some substances in the urine, such as bilirubin, medicines, dyes, and myoglobin can turn the urine red or pink, giving the false impression of hematuria.

Therefore, in order to correctly ascertain that a urine contains blood, it must be subjected to laboratory tests. The most commonly used test for the diagnosis of hematuria is called urinalysis.

The laboratory investigation of hematuria consists in the evaluation of an urine sample with a microscope, in search of red blood cells, also called erythrocytes. To be considered hematuria, most laboratories use as reference the presence of more than 10,000 erythrocytes per milliliter of urine or more than 5 erythrocytes per high power field (400x magnification).

Types of hematuria

Since there are dozens of causes for blood in urine, the proper characterization of the urine appearance helps in clinical investigation. Hematuria can be classified as:

Macroscopic hematuria (gross hematuria)

Gross hematuria can be seen with the naked eye. The urine may be brownish, reddish, pinkish or with visible blood clots. This type of hematuria can be easily recognized by the patient.

Microscopic hematuria

Microscopic hematuria cannot be seen with the naked eye, because the numbers of red blood cells in urine is very small. The appearance of the urine is completely normal, and the presence of blood can only be detected by urinalysis. This type of hematuria may exist for years until it is discovered incidentally by a urinalysis ordered for some other purpose.

Hematuria with blood clots

Blood clots in urine usually indicates a bleeding of greater volume caused by lesions of the genitourinary tract, which are often big enough to be identified through imaging tests, such as ultrasonography or computed tomography.

Persistent or transient hematuria

Hematuria may be persistent, that is, present in at least two or three properly collected urine samples (taken over a 10-day time period), or transient, that is, a hematuria that appears and disappears from an urinalysis to another.

Dysmorphic hematuria

Dysmorphic hematuria occurs when the urinalysis detects atypical (dysmorphic) red blood cells. This is usually a sign of glomerular disease.

Isolated hematuria

Isolated hematuria occurs when the patient presents no other symptom other than blood in the urine (microscopic or macroscopic). Asymptomatic isolated hematuria usually indicates a benign disease, especially if there are also no laboratory abnormalities, such as elevation of blood creatinine or presence of proteins and leukocytes in the urine.


Hematuria can originate at any point in the urinary tract, including kidneys, ureter, bladder, prostate or urethra. The most common causes of urinary bleeding are:

  • Renal cancer.
  • Bladder cancer.
  • Prostate cancer.
  • Kidney stones.
  • Urinary tract infection.
  • Benign prostatic hyperplasia.
  • Glomerulonephritis.
  • Systemic lupus erythematosus.
  • Sickle cell anemia.
  • Polycystic kidney disease.
  • Renal trauma.
  • Urethral trauma after bladder catheterization
  • Surgical or endoscopic manipulation of the urinary tract.
  • Prostate biopsy.
  • Renal biopsy.
  • Radiation cystitis (bladder injury due to radiotherapy).
  • Urinary tuberculosis.
  • Physical exertion.
  • Hypercalciuria (excessive calcium loss in the urine).
  • Endometriosis.
  • Urethritis.
  • Excessive anticoagulation.

Note: some medications, such as pyridium, quinine, rifampicin, phenytoin, and nitrofurantoin, and some foods, such as beets, may turn the urine red, mimicking hematuria.

Hematuria workup

As shown above, the causes of blood in urine are multiple and, therefore, not always simple to investigate.

For women with microscopic hematuria, the first step is to confirm that the urine sample was not collected during her period. When the woman is menstruating, there is always some contamination of menstrual blood in the urine, causing a false hematuria. In these cases, it is necessary to repeat the urinalysis after the period has ended.

Sometimes, the signs and symptoms that accompany hematuria may suggest the diagnosis, for example:

  • Young women with painful urination and blood in urine probably have cystitis.
  • Patients with hematuria associated with fever, chills, vomiting and low back pain presumably have pyelonephritis.
  • Hematuria accompanied by excruciating lumbar pain radiating to the groin is usually a sign of kidney or ureteral stone.
  • Elderly men with blood in urine and weak urinary stream should always be investigated for prostate diseases.
  • Smokers who present macroscopic hematuria, especially those older than 50 years old, should be investigated for bladder cancer.

When there is no apparent cause for hematuria, a more exhaustive investigation should be done in order to rule out some of the several causes mentioned above. Some of the imaging studies that can be used in the investigation are ultrasonography, computed tomography and cystoscopy. Laboratory tests with blood and urine samples are also frequently ordered. If a glomerular disease is suspected, a renal biopsy may be indicated.

Thin basement membrane disease (benign familial hematuria)

In some cases of isolated hematuria it is not possible to identify the cause. If the patient does not have any complaints and if all tests are normal, an annual or biennial follow-up is indicated.

Usually these patients have a condition called thin basement membrane disease, which is a harmless minor genetic alteration in the membranes of the glomeruli, that causes loss of blood in the urine. These patients usually live their lives with hematuria without any clinical repercussion.

Exercise-induced hematuria

Exercise-induced hematuria can be defined as transient gross or microscopic hematuria that occurs after strenuous exercise and resolves after a few hours or days of rest. It appears in individuals with no urinary tract pathology.

If the patient is young, healthy, has no other complaints, and the hematuria disappears with rest, there is no need for further investigation.


Since hematuria is a sign of disease and not a disease itself, there is no specific treatment for it. Each cause of hematuria has a specific treatment and, in many cases, no treatment is needed at all, such as in patients with thin membrane disease, posttraumatic hematuria or exercise-induced hematuria.

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