Blood in Urine

Red blood cells in urine, often invisible to the eye.

Blood in urine — hematuria — is often present in amounts far too small to see. A test strip can catch it anyway. Many causes are minor, but because a few are not, hidden blood is one of those markers where the right response is calm follow-up, not alarm.

What it means

Red blood cells can enter urine anywhere along the urinary tract — kidneys, ureters, bladder, or urethra. When there’s enough to change the color, it’s called gross hematuria; when only a test can detect it, microscopic hematuria. A strip detects the hemoglobin those cells carry.

Why it happens

Common causes include urinary tract infections, kidney stones, and vigorous exercise — runners see it often enough that it has its own name. Menstrual blood can also contaminate a sample. Less commonly, hematuria traces to kidney or bladder conditions that benefit from early attention, which is why persistent blood should always be evaluated.

What a result can tell you

A positive result tells you blood is present — useful information, especially alongside other markers. With UTI symptoms, it supports that picture. Without an obvious explanation, or if it repeats on retesting, it’s a clear reason to see a healthcare provider, who can find the source properly.

What it can’t tell you

A strip can’t tell where the blood is coming from or why — and it can’t distinguish true hematuria from menstrual contamination, so time your test away from your period. One clean retest after exercise-related blood is common. Persistent or unexplained positives deserve a professional look, even when you feel fine.