Can kidney stones cause blood in the urine? 

Yes, kidney stones are a frequent cause of blood in the urine, a condition medically known as haematuria. This occurs when a stone, which often has jagged or crystalline edges, moves through the urinary tract and irritates or scrapes the delicate lining of the kidneys or the ureter. In the UK, seeing blood in the urine can be alarming, but when accompanied by characteristic flank pain, it is a primary diagnostic sign used by clinicians to identify renal stones. While the blood may be clearly visible (gross haematuria), in many cases, it is only detectable via a microscopic laboratory test. 

What We will cover in this Article 

• The biological mechanism: How stones cause bleeding 

• Visible vs. Microscopic haematuria: What to look for 

• Why the colour of your urine changes during a stone attack 

• Other symptoms that typically accompany blood in the urine 

• Differentiating stone-related bleeding from other conditions 

• A data table of common causes for blood in the urine 

How Kidney Stones Cause Bleeding 

The urinary tract is lined with a highly sensitive layer of tissue called the urothelium. Kidney stones are solid masses of mineral crystals that are often far from smooth; many have sharp, needle-like protrusions or jagged surfaces. 

When a stone becomes dislodged and begins its journey from the kidney toward the bladder, it must pass through the ureter a tube only a few millimetres wide. As the ureter contracts to push the stone forward, the sharp edges of the stone can scrape against the urothelium. This mechanical irritation causes small amounts of blood to leak into the urine. Even a very small stone can cause significant bleeding if its surface is particularly abrasive. 

• Mechanical Abrasion: The physical ‘scraping’ of the stone against the urinary tract walls. 

• Inflammation: The presence of the stone causes the lining to become red, swollen, and prone to bleeding. 

• Pressure and Obstruction: Severe blockages can cause small blood vessels in the kidney to burst. 

Visible vs. Microscopic Haematuria 

It is important to understand that you may not always see the blood even if a kidney stone is present. Clinicians categorise haematuria into two types: 

1. Gross Haematuria: This is blood that is visible to the naked eye. Your urine may appear pink, bright red, or even the colour of cola or tea. It only takes a tiny amount of blood to change the colour of a full bladder of urine. 

2. Microscopic Haematuria: In this case, the urine looks completely normal. However, when a sample is tested under a microscope or with a chemical dipstick in a GP surgery, red blood cells are found. Most patients with kidney stones will have at least some level of microscopic haematuria. 

Causes and Triggers of Stone-Related Bleeding 

The primary cause of the bleeding is the movement of the stone, but certain triggers can make the bleeding more noticeable. 

The most common trigger is physical activity. If you have a ‘silent’ stone sitting in your kidney, jarring movements such as running or heavy lifting can cause the stone to shift and irritate the kidney tissue. Dehydration also plays a role; when urine is concentrated, the chemicals and minerals within it are more abrasive, and the lack of fluid means the stone is less ‘lubricated’ as it moves, increasing the likelihood of tissue damage. 

• Stone Movement: Bleeding often spikes when the stone enters the narrow ureter. 

• Exercise: Jarring the body can cause an anchored stone to scrape the kidney lining. 

• Infection: If a stone is associated with a UTI, the inflammation makes bleeding more likely. 

Differentiating Blood in Urine: Stones vs. Other Issues 

Because blood in the urine can be a symptom of various conditions, UK doctors look for associated symptoms to determine the cause. 

Table: Common Causes of Haematuria and Their Symptoms 

Condition	Appearance of Urine	Accompanying Symptoms	Pain Level
Kidney Stone	Pink, red, or cola-coloured	Sharp waves of flank/groin pain	Very High
Cystitis (UTI)	Cloudy or pink-tinged	Burning peeing, frequent urge	Moderate
Kidney Infection	Dark or cloudy	Fever, chills, back ache	High/Aching
Bladder Cancer	Bright red (often painless)	Often no other early symptoms	Usually None
Extreme Exercise	Tea-coloured	Muscle soreness	Low

In the case of a kidney stone, the blood is almost always accompanied by ‘renal colic’—intense, wave-like pain in the side or back. If you see blood in your urine but feel absolutely no pain, it is vital to see a doctor urgently, as painless bleeding can sometimes be a sign of other serious conditions. 

To Summarise 

Kidney stones are a leading cause of blood in the urine due to the mechanical scraping of jagged crystals against the urinary tract. Whether the blood is clearly visible as pink or red urine, or only detectable under a microscope, it serves as a critical clinical marker for stone movement. While the sight of blood can be frightening, it is usually a result of minor tissue irritation rather than a life-threatening haemorrhage. However, any instance of blood in the urine requires a professional medical evaluation. 

If you experience severe, sudden, or worsening symptoms, such as intense pain in your side, visible blood in your urine, or a high fever with chills, call 999 immediately. 

Authority snapshot 

This article was reviewed by Dr. Stefan Petrov, a UK-trained physician with an MBBS and postgraduate certifications including ACLS and BLS. Dr. Petrov has managed hundreds of cases involving haematuria in NHS emergency departments and surgical wards. This guide follows clinical standards to ensure the information regarding renal symptoms and emergency markers is accurate and safe for the public