Seeing blood in the urine can be frightening. One possible cause is a kidney stone. Kidney stones are hard deposits made of minerals and salts that form in the kidneys and may move through the urinary tract. As they move, they can cause pain, irritation, blockage, and bleeding.
Blood in the urine is called hematuria. Sometimes it is visible, which is known as gross hematuria. In other cases, it is found only on a urine test, which is called microscopic hematuria. Even when blood is not visible, it can still matter and may still need medical evaluation depending on the situation.
Kidney stones are a common cause of hematuria, but they are not the only cause. Blood in the urine is a symptom, not a diagnosis. That is why it should never be ignored, even when a stone seems likely.
What Causes Kidney Stones?
Kidney stones form when certain substances in the urine become concentrated enough to crystallize. Over time, these crystals can grow into a stone. Common stone types include calcium stones, uric acid stones, struvite stones, and cystine stones. Because different stone types can form for different reasons, prevention should be based on the stone type whenever possible.
Some people are at higher risk than others. Risk can be increased by a personal history of stones, a family history of stones, recurrent dehydration, gout, certain bowel disorders, and some metabolic conditions.
Why Kidney Stones Can Cause Blood in the Urine
Kidney stones can cause hematuria in more than one way. As a stone moves through the urinary tract, it may irritate and injure the delicate lining of the kidney, ureter, or bladder. That local tissue injury can lead to bleeding.
However, bleeding is not always caused only by surface irritation. If a stone blocks the flow of urine, pressure can build up behind the obstruction. This may cause distension of the collecting system or ureter, local inflammation, and increased retrograde pressure. In some cases, this pressure-related stress can also contribute to hematuria and pain. That makes the clinical pathway more accurate as:
stone → obstruction → pressure buildup and tissue stress → hematuria.
This distinction matters because a stone that is causing obstruction may need more urgent medical attention, especially if infection is also present. A stone plus obstruction plus possible infection can become a medical urgency.
Not All Blood in the Urine Means the Same Thing
Although stones are a common urinary cause of hematuria, not all hematuria comes from a stone rubbing the urinary tract. In some cases, blood in the urine may come from a glomerular cause, meaning a problem in the kidney’s filtering barrier rather than the lower urinary tract.
The appearance of the urine may offer clues, although it is not a reliable diagnosis by itself. In some cases, bright red or pink urine, especially with clots, may point more toward a urologic source, while tea-colored, cola-colored, or dark brown urine may suggest a glomerular source. These are clinical clues, not absolute rules.
Microscopic Hematuria Still Matters
Microscopic hematuria means blood is present in the urine but cannot be seen with the naked eye. It is often found incidentally during a urinalysis. Even though it may be invisible, it should not automatically be dismissed. Depending on the patient’s age, symptoms, risk factors, and medical history, it may still require evaluation.
It is also important to remember that the absence of visible blood does not rule out a kidney stone. Some stones cause only microscopic hematuria, and some may even be present when blood is not detected at every moment. Small stones may also cause few symptoms or no symptoms at all.
Symptoms That May Happen With a Kidney Stone
Kidney stones can cause a range of symptoms, including:
- Sharp pain in the back, side, lower abdomen, or groin
- Nausea or vomiting
- Pain with urination
- Frequent urination or urgency
- Difficulty urinating or low urine output
- Cloudy or foul-smelling urine
- Visible or microscopic blood in the urine
Not every stone causes severe classic renal colic. Some may cause only mild discomfort, intermittent symptoms, or be found incidentally on imaging.
A Special Warning About Painless Blood in the Urine
Painless blood in the urine should never be ignored.
Although some stones may not cause dramatic pain, hematuria without pain should prompt medical evaluation because it can also be linked to other causes, including infection, glomerular disease, or urologic tumors. Patients should not assume that blood in the urine is “just a stone,” especially when there is no typical stone pain or when the bleeding keeps happening.
How Long Does It Take to Pass a Kidney Stone?
That depends on more than just size. Passage may also depend on the stone’s location, shape, degree of obstruction, and the patient’s symptoms.
Some small stones may pass within days or over a couple of weeks. Others may not pass on their own and may need medication or a procedure. A stone that becomes stuck can block urine flow and cause pain or bleeding.
How Kidney Stones Are Evaluated
When a kidney stone is suspected, evaluation is not only about “finding the stone.” It may also aim to:
- confirm whether there is obstruction
- look for signs of infection
- assess the effect on kidney function
- determine whether the bleeding could have another cause
Testing may include:
- Urinalysis, to look for blood, infection, and crystals
- Blood tests, to check kidney function and electrolyte levels
- Imaging, such as CT scan or ultrasound, to locate the stone and look for blockage
For people who form stones repeatedly, clinicians may sometimes recommend a more detailed metabolic evaluation, which may include 24-hour urine testing or other studies depending on the case.
Treatment and Symptom Relief
Treatment depends on the size and location of the stone, whether there is obstruction, whether infection is present, how severe the pain is, and whether kidney function is affected.
Pain Management
Kidney stone pain can be intense. Pain relief should be chosen carefully, especially in people with chronic kidney disease, dehydration, or other medical conditions.
Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen or naproxen are sometimes used for kidney stone pain, but they are not safe for everyone. In some patients, especially those who are dehydrated or already have reduced kidney function, NSAIDs may reduce blood flow to the kidneys and increase the risk of kidney injury. Patients should not assume that over-the-counter pain medicine is automatically safe.
Hydration
Hydration is often part of kidney stone management because it may help support urine flow and reduce urine concentration. But there is an important difference between sensible hydration and forcing large amounts of water.
Trying to drink excessive amounts of water may not be appropriate in people with advanced chronic kidney disease, heart failure, severe vomiting, or a fluid restriction. Fluid advice should be individualized.
Medications and Procedures
Some people are prescribed medication to help relax the ureter and improve stone passage. Others may need antibiotics if infection is suspected. If a stone is too large to pass, causes persistent obstruction, is associated with infection, or leads to uncontrolled pain, a procedure may be necessary.
Prevention: Lowering the Risk of Future Stones
Prevention should not be one-size-fits-all. The best prevention plan usually depends on the stone type, urine chemistry, medical history, and sometimes the results of a metabolic evaluation.
Sodium
Reducing excess sodium is especially important for many people who form calcium-based stones. A high-sodium diet can increase the amount of calcium excreted into the urine, which may make calcium stone formation more likely.
Animal Protein
Moderation of animal protein may help in selected patients. Diets high in animal protein can lower urine pH and raise uric acid levels, which may contribute to some types of stones.
Calcium
Many patients assume they should cut calcium out of their diet, but that is not always correct and may sometimes be counterproductive. Calcium intake should be discussed with a clinician rather than reduced on a patient’s own.
Supplements and Home Remedies
Supplements and home remedies are not always safe or appropriate, especially for people with kidney disease or people taking multiple medications. Patients should check with their care team before starting them.
When Should You Seek Medical Attention Right Away?
Seek prompt medical care if blood in the urine happens along with any of the following:
- Fever or chills
- Severe or worsening pain
- Repeated vomiting
- Difficulty passing urine
- Very little urine output
- Dizziness or weakness
- A known single kidney
- Pregnancy
- Blood clots in the urine
- Blood in the urine without pain, especially if it keeps happening
These may be warning signs of obstruction, infection, dehydration, or another serious condition that needs urgent evaluation.
Nephrologist or Urologist: Who Helps With What?
A urologist often becomes especially important when there is obstruction, a need for a procedure, or another structural issue in the urinary tract.
A nephrologist may be especially important when there is chronic kidney disease, concern about reduced kidney function, glomerular causes of hematuria, or a need for a more complex metabolic evaluation. In some situations, both specialists may be involved.
Questions to Ask Your Doctor
- Could the blood be coming from a kidney stone or another cause?
- Is there any sign of blockage or infection?
- Do I need imaging or follow-up testing?
- What kind of stone do I have, if known?
- What diet or fluid changes are safe for me given my kidney health?
- Do I need a more detailed urine or metabolic evaluation?
The Bottom Line
Kidney stones are a common cause of hematuria, but they are not the only cause, and the bleeding does not always happen only because a stone “scratches” the urinary tract. Stones may also cause obstruction, increased pressure, inflammation, and kidney stress. The goal is not only to identify the source of bleeding, but also to protect kidney function, detect obstruction early, and avoid missing another serious diagnosis. Patient-friendly guidance from organizations such as the National Kidney Foundation and NIDDK supports that hematuria deserves proper evaluation rather than self-diagnosis.
FAQs
What does blood in the urine mean if I have a kidney stone?
Blood in the urine can happen when a kidney stone irritates the urinary tract or blocks the flow of urine, which can raise pressure and cause local inflammation or bleeding. However, blood in the urine does not always mean a stone is the only cause, so medical evaluation may still be needed.
Can a kidney stone cause blood in the urine without severe pain?
Yes. Some kidney stones cause severe pain, but others may cause only mild discomfort, intermittent symptoms, or even no obvious pain. Painless blood in the urine should still be evaluated.
Is microscopic hematuria serious if I cannot see the blood?
It can be. Microscopic hematuria means blood is present even though it is not visible. In some cases it is found incidentally on a urine test, but it may still need evaluation depending on your symptoms, age, and medical history.
When is blood in the urine an emergency?
Blood in the urine needs urgent evaluation if it happens with fever, chills, severe pain, repeated vomiting, trouble urinating, very low urine output, weakness, clots, or possible signs of infection or obstruction.
Can drinking more water always help pass a kidney stone?
Not always. Hydration may help some people, but forcing large amounts of water is not appropriate for everyone, especially people with advanced kidney disease, heart failure, severe vomiting, or fluid restrictions.
Should I stop calcium or take supplements to prevent stones on my own?
No. Reducing calcium on your own is not always helpful and may sometimes be counterproductive. Supplements and home remedies are not always safe either, especially if you have kidney disease. Prevention should be individualized.
Do recurrent kidney stones need more testing?
Sometimes, yes. People who form stones repeatedly may need a more detailed evaluation, such as urine chemistry or 24-hour urine testing, to help identify the cause and guide prevention.