Kidney stones can come in a variety of colors, which can indicate what type of stone it is. The color of a kidney stone provides clues about its composition. While black kidney stones are possible, they are very rare. Much more common kidney stone colors are brown, yellow, gold, or tan.
What are kidney stones?
Kidney stones form when minerals and salts in the urine crystallize and stick together. These stone-forming minerals can include calcium, oxalate, uric acid, cysteine, and struvite. The most common type of kidney stones is calcium oxalate stones.
Kidney stones can range in size from a tiny grain of sand to larger than a golf ball. Smaller kidney stones may be able to pass through the urinary tract on their own, while larger ones can get stuck and block the flow of urine.
Kidney stones can cause severe pain, most commonly in the back, side, lower abdomen or groin area. Other symptoms of kidney stones can include:
- Painful urination
- Blood in the urine
- Cloudy or foul-smelling urine
- Nausea and vomiting
- Fever and chills
If the kidney stone does not pass on its own, treatment may be required. This can include pain medication, fluids, vibration or shock wave therapy, surgery and more. The goal is to try to help pass the stone or break it into smaller pieces that can more easily travel through the urinary system.
What causes different kidney stone colors?
The mineral composition of the kidney stone affects its color. Here are some of the common colors of kidney stones and what they may indicate:
- Brown: Most commonly calcium oxalate stones. Oxalate is a compound found in many foods including spinach, nuts, strawberries, tea, wheat bran and chocolate.
- Yellow or gold: Also suggests calcium stones, specifically calcium phosphate stones. Eating too much salty, high-oxalate, or animal-protein rich foods can contribute.
- Pink or red: Indicates the presence of blood in the urine as the stones pass. Not necessarily the stone’s true color.
- Green: Rare type of stone made of uric acid. Gout can increase uric acid levels in urine.
- White: Often struvite stones, made of magnesium ammonium phosphate. More common in women and can be related to urinary tract infections.
- Black: Very rare pigmented calcium oxalate stones. The pigment may come from medications, food or blood.
Are black kidney stones common?
While it is possible for kidney stones to appear black, this is relatively uncommon. Black kidney stones make up less than 1% of all stones. The black color is thought to come from pigments absorbed by the stone.
Some potential sources of the black pigment include:
- Medications like anti-malarials and anti-inflammatories.
- Foods and supplements containing pigments, like rhubarb and aloe.
- Metabolic disorders leading to excess pigment accumulation.
- Blood, such as from urinary tract bleeding.
The main type of black kidney stones is black calcium oxalate stones. The oxalate gives them the basic crystal shape while the pigment adds the black color.
It may be difficult to tell a stone is black until it is passed and can be directly examined. Stones within the kidneys often appear lighter on imaging tests. The dark coloring becomes more evident when outside the body.
Signs that you may have black kidney stones
Black kidney stones will cause the same symptoms as other stones, so the color alone does not provide specific clues. Symptoms to watch for include:
- Severe pain in the back, abdomen or groin
- Pain that comes in waves and fluctuates in intensity
- Pain on one side of the body or the other
- Nausea and vomiting
- Difficulty urinating or blood in the urine
- Feeling an urgent need to urinate
- Fever and chills
Some factors that may point to black kidney stones include:
- Being prescribed medications that cause visible discoloration of the urine
- Having a condition that leads to excessive pigment in the kidneys and urinary tract
- Noticing very dark or black coloration of your urine
- Having a prior history of kidney stones, especially black ones
Catching kidney stones early allows quick treatment to relieve symptoms and prevent complications. Contact your doctor right away if you suspect you have a kidney stone.
Diagnosing black kidney stones
To diagnose kidney stones, doctors use imaging tests to visualize the kidneys and urinary tract. This can identify the size, location and number of any stones. Some tests used include:
- CT scan: Uses x-rays and computer imaging to create cross-sectional pictures. Good for identifying all types of kidney stones.
- Ultrasound: Uses sound waves to create images of kidneys and urinary tract. Ultrasound is also useful during pregnancy.
- X-rays: Help locate kidney stones and can confirm if a stone has passed after symptoms resolve.
- IVU: Intravenous pyelogram involves injecting dye into a vein and taking x-rays as it travels through the kidneys.
These tests may not clearly show that a stone is black, but they can reveal its size and location. Any stones that are passed can be directly examined, making it easier to identify black coloring.
Other tests that may be done to help diagnose kidney stones include:
- Blood tests to assess kidney function and check for signs of infection or gout.
- Urine analysis to look for blood or excess crystal-forming minerals.
- Urine culture to identify any bacteria present.
How are black kidney stones treated?
The treatment approach for black kidney stones involves:
- Pain management with medications such as non-steroidal anti-inflammatories, opioids, and antispasmodics.
- Liquids and hydration to help flush out the urinary system.
- Medications that relax the ureter to allow stone passage, or alpha blockers to relax the ureter.
- Lithotripsy, using sound waves to break up larger stones.
- Surgery such as cystoscopy to manually remove stones, or ureteroscopy to remove impacted stones.
The specific treatment depends on the stone’s location and size. The goal is to relieve symptoms and allow stone passage or removal where needed. The black color of the kidney stones does not change the treatment approach.
Preventing black kidney stones
Many of the same dietary and lifestyle measures can help prevent both black and non-black kidney stones. Recommendations include:
- Drinking plenty of water, around 2 to 3 liters daily.
- Limiting sodium and animal protein intake.
- Getting enough calcium from foods, but avoiding excess supplements.
- Reducing oxalate-rich foods like spinach, nuts, chocolate.
- Eating less sugar, which can increase calcium in the urine.
Your doctor may recommend specific dietary changes or medications after analyzing your stone. Identifying any underlying conditions contributing to recurrent kidney stones is also important.
Being aware of your family history and any personal risk factors for kidney stones allows appropriate preventive steps. Contact your urologist if you have a history of kidney stones.
When to seek emergency treatment
Most kidney stones will try to pass on their own, but some require prompt medical treatment. Seek emergency care for symptoms such as:
- Unmanageable pain not relieved by medications
- Persistent nausea and vomiting
- Fever and chills
- Pus or blood in the urine
- Inability to urinate despite feeling the urge
- Confusion, fatigue and reduced urine output
People at higher risk who need emergency kidney stone care include:
- Those with only one functioning kidney
- On chronic dialysis
- With a kidney transplant
- With a known urinary obstruction or large stone
- Who are pregnant
Prompt medical care can provide relief from symptoms, prevent infection, and avoid lasting kidney damage.
Are there complications from black kidney stones?
Black kidney stones can potentially cause the same complications as other stones if left untreated. Complications can include:
- Infections: Bacteria can get trapped behind an obstructing stone and cause a kidney infection (pyelonephritis).
- Urine blockage: Stones may obstruct the ureters or urethra, allowing urine to back up and injure the kidneys.
- Kidney damage: Prolonged obstruction and pressure can damage kidney tissue and function.
- Recurring stones: People who have had stones are at higher risk of developing them again.
Rarely, extensive kidney stone disease can lead to chronic kidney disease or failure requiring dialysis. However, most complications can be avoided with prompt treatment when kidney stone symptoms first appear.
Are black kidney stones more serious than regular stones?
In most cases, black kidney stones are not necessarily more serious than non-black stones. They are simply an uncommon variety of stones most often made up of calcium oxalate.
Features that determine how serious any kidney stone may be include:
- Stone size – larger stones are more likely to obstruct
- Stone location – stones blocking ureters or urethra can prevent urine flow
- Presence of infection
- Underlying kidney problems
- Genetic and medical factors increasing recurrent stone risk
So while an unusually dark, black stone may seem concerning, its true severity depends on these other factors. Small black kidney stones may pass uneventfully while larger or obstructing black stones can cause complications.
The black pigment itself is not necessarily harmful. But any kidney stones should be evaluated by a urologist, even if symptoms resolve.
Conclusion
While most kidney stones are yellowish to brown in color, black kidney stones can occasionally occur. These darker stones are pigmented by compounds that were absorbed into the stone matrix, such as from food, medicine or blood.
Black kidney stones typically cause the same symptoms and need the same treatment as other types of stones. That is because their black color alone does not make them more dangerous. However, any kidney stones that cause severe symptoms, obstruction or infection require prompt medical care.
Being aware of the first signs of kidney stones allows quick action to relieve pain, prevent complications and analyze stone composition. Anyone who has passed an unusually dark or black stone should have it analyzed and follow up with their urologist.
With the right precautions and ongoing monitoring, black kidney stones can often be prevented from recurring in the future.
Kidney Stone Symptoms Table
| Type of Symptom | Specific Symptoms |
|---|---|
| Pain | Lower back, abdominal or groin pain |
| Pain that comes and goes in waves | |
| Pain on one side or the other | |
| Urinary | Burning with urination |
| Blood in the urine | |
| Inability to urinate despite urge | |
| Constant urge to urinate | |
| Other | Nausea and vomiting |
| Fever and chills |