Blood in Urine (Hematuria): Causes and Diagnosis

Blood in the urine is most often discovered during a general urine test: the dipstick reacts to hemoglobin, so it can be positive even when the urine contains free hemoglobin or myoglobin (for example after muscle breakdown) rather than red cells themselves. That is why the AUA/SUFU guideline defines microhematuria as at least 3 red blood cells per high-power field on microscopic examination of a single specimen, not just a positive dipstick. An earlier version of the AUA guideline stressed that a positive dipstick should not lead to imaging or further investigation without microscopic confirmation.

False alarms are more common than you might think. Red urine can be caused by beetroot, some food colorings and drugs (for example rifampicin), and real blood by menstruation or spotting that 'gets into' the sample, especially when urine is not collected midstream. Conversely, urine may look normal on dipsticks even though red cells are present if the sample was diluted or stood too long. So before any panic it is worth repeating a general urine test with sediment assessment, after the period, from a correctly collected sample.

The basic diagnostic question is: is the blood leaking through a damaged kidney glomerular filter (glomerular, nephrological hematuria), or is it bleeding somewhere along the path from the renal pelvis to the urethra (non-glomerular, urological hematuria)? The answer determines whether the patient goes to a nephrologist or a urologist, and often to both.

Clues come from the color and character of the bleeding and from microscopic examination of the urine sediment. Tea- or cola-colored urine, without clots, with accompanying proteinuria, swelling or hypertension, suggests a glomerular cause. Fresh bright-red blood, clots, colicky pain or bladder symptoms (frequency, urgency) suggest a urological source. Microscopically, deformed red cells (dysmorphic, especially acanthocytes) and red cell casts point to the glomeruli.

This knowledge has practical importance: a bare 'red cells in urine' result from an automated analyzer does not say where they come from. If you suspect a glomerular problem (swelling, foamy urine, blood pressure), ask your doctor for an assessment of the urine sediment by an experienced analyst or for a referral to a nephrologist rather than stopping at a cell count.

So there is no single answer to 'where does blood in urine come from'. What matters is orderly clarification: first excluding infection and transient factors, then assessing the kidneys (ACR, eGFR, sediment), and then, depending on risk, assessing the urinary tract with cystoscopy and imaging. In our knowledge base we describe kidney stones and benign prostatic hyperplasia, which are among the most common urological causes of hematuria.

We read this as follows: cancer is a rare but real explanation of microhematuria, and its rarity changes with risk. In a 25-year-old non-smoking woman the probability is negligible; in a 65-year-old smoker it is many times greater. That is why modern guidelines moved away from the 'everyone over 35 gets a cystoscopy' scheme (recommended by the 2012 version) toward assessing individual risk. Visible hematuria, on the other hand, remains a signal that usually needs a full urological assessment whether or not it clears up by itself.

Red cells can appear in urine after intense exertion, especially running and sprints. A study in healthy runners showed that exercise hematuria is linked to the intensity of weight-bearing exercise rather than to its duration.

Practical consequence: if blood appeared in your urine after a marathon or a hard interval session, it is reasonable to wait and repeat the test after a few days of rest. If, however, it recurs without any connection to exercise, do not dismiss it. The same goes for menstruation: it is best to collect the urine sample after it ends, midstream, and for spotting outside the period also to consult a gynecologist, because the blood may come from the genital tract rather than the urinary tract.

An important note on anticoagulants: they can worsen bleeding, but they should not be automatically accepted as the only explanation for hematuria, because they may reveal an existing lesion. Taking an anticoagulant should usually not be the sole reason to skip the workup. The doctor always decides the scope of testing, and the drug must never be stopped on your own.

In young adults without proteinuria and without other symptoms, persistent microhematuria usually does not mean cancer; it more often results from benign glomerular disease. The question is whether it deserves long-term follow-up.

Practical conclusion: the relative risk is high, the absolute risk small. In a young person with persistent microhematuria it makes sense to at least periodically check blood pressure, eGFR and ACR, and to see a nephrologist if proteinuria or a fall in eGFR appears. It is not a reason for panic but for calm, systematic follow-up.

Limitations: the AUA/SUFU guidelines are American and rely mainly on studies of Western populations; European urological recommendations may differ in some thresholds. The Korean study involved people from a screening program and so does not represent all patients presenting with symptoms. Cancer yield in the meta-analysis is averaged, and individual risk depends on age, sex, smoking and exposures. This article does not replace a consultation and should not delay a visit to the doctor if visible blood appears in the urine.

From the reader's perspective three things matter most. First, confirm blood with a microscopic examination rather than the dipstick alone, and exclude transient factors (menstruation, intense training, infection). Second, if blood persists or is visible to the naked eye, do not wait: ask for a risk classification and further workup. Third, do not be afraid to ask about the kidneys: ACR, eGFR and blood pressure are simple tests that often clarify whether the problem lies in the glomeruli or the urinary tract.