Blood in the urine, known as hematuria, can be alarming. Hematuria is categorized as either gross (visible blood, turning urine pink, red, or cola-colored) or microscopic (only detectable under a microscope). While dehydration alone is not a direct cause of hematuria, severe dehydration can lead to conditions that result in blood appearing in the urine. Any instance of blood in the urine requires professional medical investigation to rule out serious underlying issues.
How Dehydration Affects Urine Concentration
Dehydration occurs when the body loses more fluid than it takes in, prompting the kidneys to conserve water. This results in highly concentrated urine containing high levels of dissolved waste products and minerals. The increased concentration can irritate the delicate lining of the urinary tract and the bladder, potentially leading to minor bleeding and microscopic hematuria.
Severe dehydration can cause a reduction in blood flow to the kidneys, known as renal ischemia. This decreased blood supply forces the kidneys to work harder with fewer resources. Such stress can temporarily impair the filtering units (nephrons), potentially damaging the filtering mechanisms and allowing red blood cells to leak into the urine.
A rare example is exercise-induced hematuria, sometimes called “march hematuria,” which commonly affects long-distance runners or individuals engaging in intense, prolonged physical activity. This microscopic bleeding is often linked to strenuous exertion combined with poor hydration. Mechanisms involved can include reduced blood flow to the kidneys and physical trauma, such as the bladder walls repeatedly hitting each other during high-impact exercise. Dehydration acts as a contributing factor that exacerbates physical stress on the urinary system.
More Common Causes of Hematuria
While dehydration can contribute, blood in the urine is far more often a symptom of other conditions affecting the urinary system. Urinary Tract Infections (UTIs) are one of the most frequent causes of hematuria, particularly in women. UTIs occur when bacteria colonize the urinary tract, causing inflammation and irritation of the lining of the urethra or bladder, which leads to bleeding.
Inadequate hydration is a major factor in the formation of kidney stones. Low fluid intake causes salts and minerals in the urine to become highly saturated, leading to crystallization and stone formation. As these stones pass through the narrow ureters, they can injure the lining of the urinary tract, causing visible bleeding.
Other serious conditions must be considered, including kidney or bladder diseases and injuries. Kidney diseases, such as glomerulonephritis, can damage the glomeruli (the small blood vessels that filter blood), allowing blood cells to escape into the urine. Trauma or injury to the kidneys, bladder, or urethra can also cause immediate bleeding. Certain medications, such as blood thinners, increase the likelihood of hematuria. Hematuria may also indicate serious conditions like kidney or bladder cancers, making professional evaluation necessary.
When to Seek Medical Attention
Any instance of visible blood in the urine (gross hematuria) should prompt an immediate consultation with a healthcare provider. Visible blood requires a thorough evaluation to determine the underlying cause and rule out serious conditions. Even if you suspect the cause is minor dehydration, a professional diagnosis is necessary to ensure the bleeding is not a sign of infection, stones, or malignancy.
Urgent medical care is necessary if hematuria is accompanied by severe symptoms, including fever, chills, severe pain in the side, back, or abdomen, or an inability to urinate. If microscopic hematuria is detected on a routine lab test, follow-up testing is required. If hematuria from strenuous activity does not clear up within 24 to 72 hours, medical attention is also warranted.