What is a kidney stone?
Kidney stone, also called kidney stone or kidney lithiasis, is a very common disease, caused by crystallization of mineral salts present in the urine, which group together and form, literally, a small stone inside the urinary tract.
When this stone is large enough to obstruct the flow of urine, the internal structures of the kidney may become enlarged, which causes what is known as renal colic.
Renal colic is one of the most painful events that a patient can experience in their lifetime. The pain caused by kidney stones is often described as being worse than childbirth, bone fractures, gunshot wounds, or burns.
How do kidney stones form?
A kidney stone is exactly what the name says, a solid formation composed of minerals that appears inside the kidneys. More than 70% of stones are composed of calcium salts, such as calcium oxalate and calcium phosphate. There are also stones based on uric acid, struvite (magnesium + ammonium + phosphate), and cystine.
Understanding stone formation is simple. Imagine a glass full of clear, transparent water. If we throw a little salt into it, it will dilute and make the water a little cloudy. If we continue to pour salt into the glass, the water will become less and less clear, until the point where the salt begins to precipitate at the bottom of the glass. The precipitation happens when the water becomes oversaturated with salt, that is, the amount of water present is no longer sufficient to dilute the salt.
This is the principle of stone formation. When the amount of water in the urine is not enough to dissolve all the salts present in the urine, the salts return to their solid form and precipitate in the urinary tract. The salts precipitated in the urine tend to clump together, forming, over time, stones.
This precipitation of salts present in the urine occurs basically for two reasons: lack of water to dilute or too many salts to be diluted.
Most cases of kidney stones occur due to a lack of water to dilute the urine properly, and the cause is too little fluid intake.
However, there is a group of patients who, even if they drink plenty of water throughout the day, continue to form stones. These individuals usually have alterations in the natural urine composition, with an excess of mineral salts, especially calcium. The amount of calcium in the urine is so large that even with a good intake of water it can still precipitate.
Risk factors of kidney stones
Having enough water in the urine is essential to prevent the formation of stones. Patients who tend to develop stones drink on average 300 to 500 ml less water per day compared to people who have never had a kidney stone.
Patients who live in tropical climates or work in very hot places should try to keep themselves well hydrated to avoid producing too concentrated urine.
The type of liquid ingested does not have much importance. There are still no definitive studies that can state that one type of liquid is superior to another. Some studies suggest that besides water, orange juice, coffee, and teas (including the famous stonebreaker tea) may have some benefit.
Grapefruit juice, on the other hand, seems to be harmful, increasing the risk of stone formation.
As for alcoholic beverages, there is controversy, with studies indicating an increase in stone formation and others suggesting a reduction, especially with wine consumption.
Vitamin C increases the renal excretion of oxalate, and some studies suggest that its excessive consumption may increase the risk of calcium oxalate kidney stones (read: VITAMIN C – Importance, effects and rich foods)
People who have had at least one episode of kidney stones, or who have a family history of kidney stones, should urinate at least 2 liters a day.
Since no one is going to collect urine all day to measure the volume, a tip is to monitor the color of the urine. Well-diluted urine has a weak odor and a very clear, almost transparent color (read: STRONG-Smelling Urine). If your urine is very yellowish, this indicates dehydration.
Regarding diet, there are some habits that can increase the incidence of kidney stones, especially if the patient already has higher than average urine calcium concentrations.
Diets high in salt, protein, and sugars are risk factors. Interestingly, although most stones are composed of calcium and arise from excess calcium in the urine, there is no need to restrict calcium consumption in the diet. Restriction, in fact, can be harmful. If you are already losing too much calcium in your urine and you do not replace it with your diet, your body will get the calcium it needs from your bones, which can lead to early osteoporosis .
The only caution should be with calcium supplements, since their consumption, especially when fasting, seems to increase the risk of kidney stones.
Other risk factors for the appearance of stones are obesity, age over 40, hypertension, gout, diabetes, being male, and very rapid weight gain.
It is important to remember that there are also kidney stones formed by the precipitation of some drugs in the kidneys. Several medications can have the side effect of stone formation. The most common include: indinavir, atazanavir, guaifenesin, trianthenesin, silicate, and sulfa drugs such as sulfasalazine and sulfadiazine.
Symptoms of kidney stones
Many patients have stones in their kidneys and do not experience any symptoms. If the stone forms inside the kidney and remains stationary inside the kidney, the patient can remain asymptomatic for years.
Many people discover the kidney stone by chance, during an abdominal imaging exam, such as an ultrasound or CT scan, requested for some other reason.
Very small stones, smaller than 3 millimeters (0.3 centimeters), can travel through the entire urinary system and be eliminated in the urine without causing major symptoms. The patient starts urinating and suddenly notices that a pebble has fallen into the toilet bowl.
The classic symptom of kidney stones, called renal colic, appears when a stone of at least 4 mm (0.4 cm) is impacted in the kidney or somewhere in the ureter (tube that carries urine from the kidney to the bladder), causing obstruction and dilatation of the urinary system.
Renal colic is usually an excruciating low back pain, which is often the worst pain the patient has ever had. Renal colic makes the patient restless, fidgeting all the time, looking in vain for a position that will provide relief.
Unlike back pain, which improves with rest and worsens with movement, renal colic hurts intensely, no matter what the patient does. Sometimes the pain is so intense that it is accompanied by nausea and vomiting. Blood in the urine is frequent and occurs due to direct stone injury in the ureter.
Renal colic usually has three phases:
- The pain starts suddenly and peaks in about 1 or 2 hours.
- After reaching its apex, the pain remains severe for another 1 to 4 hours, on average, making the patient extremely restless.
- The pain spontaneously starts to alleviate and over a further 2 hours tends to disappear.
In some unfortunate ones, the entire process takes more than 12 hours, if they do not seek medical attention.
If the stone is impacted in the lower half of the ureter, renal colic can radiate to the leg, labia, or testicles (read: Causes of Pain in the Testicles ).
It is also possible that the stone can cross the entire ureter, being impacted only in the urethra, which is the smallest point in the urinary system. In this case, pain occurs in the pelvic region and is accompanied by burning when urinating and bleeding. Often, the patient is able to recognize that there is a stone in his urethra, about to come out.
Diagnosis of kidney stones is usually made with an imaging test. The simplest is ultrasonography.
The disadvantage of ultrasound is its poor ability to identify stones impacted in the middle of the ureter, because intestinal gas hinders the formation of a clear image.
The best exam is the CT scan, which can identify the stones anywhere in the urinary system, even without the use of contrast.
The imaging exams in addition to diagnosing the stone are also able to measure its size, information that is important for the doctor to try to predict what will happen in the coming days.
Natural history of the stone
The location and size are the factors that define whether the stone has a chance of coming out spontaneously or whether a urological procedure will be necessary to remove it.
Stones smaller than 5 mm (0.5 cm), especially if they are located at the end of the ureter, usually pass spontaneously through the urine without treatment. The stone takes, on average, 8 to 14 days to be expelled. However, depending on the location, the time can be up to one month.
Less than 20% of the patients with stones smaller than 5 mm need some medical intervention to remove their kidney stone.
Above 5 mm, the larger the stone, the smaller the chance that it will be eliminated spontaneously. 60% of kidney stones between 5 and 7 mm (0.5 and 0.7 cm) are eliminated without treatment; this rate drops to less than 50% for stones between 7 and 9 mm (0.7 and 0.9 cm).
As for large stones, larger than 9 mm (0.9 cm), only 25% come out spontaneously, even then, only if they are already at the end of the ureter.
Stones larger than 10 mm (1 cm) located at the beginning of the ureter, close to the kidney, usually do not come out on their own, because they are up to three times larger than the average diameter of the ureter.
These large stones can become impacted in the ureter, causing an obstruction to the drainage of urine and consequent dilatation of the kidney, which we call hydronephrosis.
Hydronephrosis is a serious complication, as the obstruction of the urine passage and the dilatation of internal structures can cause permanent damage to the kidney if treated in time.
Both ultrasound and CT scan can easily identify a hydronephrosis.
Treatment of renal colic crisis
The first step in treating renal colic is obviously to relieve the patient’s pain. The most commonly used medications are anti-inflammatory drugs and opioid analgesics (morphine derivatives).
Most patients with renal colic can be treated conservatively, with medication to control pain and hydration until the stone is eliminated spontaneously.
If hydronephrosis is present, it should be corrected as soon as possible, because the longer the obstruction lasts, the greater the chance of irreversible damage to the obstructed kidney. Obstructed patients should be referred to a urologist.
Treatment outside the renal colic crisis
Once the patient’s pain is controlled and a kidney stone of less than 10 mm is diagnosed with no signs of complications, the patient can be treated at home, waiting for spontaneous elimination of the stone.
Usually the patient is released home medicated with anti-inflammatory drugs to control the pain and drugs that relax the ureter, which facilitates the passage of the stone towards the bladder.
The most commonly used drugs for this purpose are Tansulosin (a drug also used in benign prostatic hyperplasia) or Nifedipine (a drug also used to treat high blood pressure).
If the patient has stones larger than 1 cm, pain that is difficult to control, signs of kidney obstruction (hydronephrosis), signs of urinary infection, or if after 4 to 6 weeks the stone has not come out spontaneously, evaluation by a urologist is indicated.
To find out what diet is indicated for those with recurrent kidney stones, read: Diet for those with kidney stones.
Are there medicines that dissolve kidney stones?
If the stone is mainly composed of uric acid, alkalinizing the urine with bicarbonate or potassium citrate (Litocit) can help dissolve the stone. This is the only situation in which dissolving stones is possible.
However, the vast majority of kidney stones are composed of calcium salts. In these cases, unfortunately, there is no way to dissolve the stones that have already formed.
Be careful. Some dishonest companies take advantage of the fact that most stones come out on their own and that some can change size spontaneously in order to sell “natural miracle products”.
There are dozens of fake websites advocating the use of substances that are supposed to dissolve kidney stones. These treatments are not scientifically proven. No International Society of Urology or Nephrology recommends the use of calcium-based stone dissolving substances.
What about stonecrop tea?
The famous stone-breaker tea does not break any stones. But it seems to be effective in preventing kidney stones. If the patient already has a calcium stone formed, the tea works as well as any other liquid, including water. However, if taken frequently it seems to decrease the formation of new stones, reducing the incidence of new kidney stones.
If the kidney stone is too large or complications arise, such as a urinary tract infection or an obstruction in the functioning of one of the kidneys, the only way to treat the patient is through medical intervention.
The treatment of kidney stones has evolved a lot over the years and today there are several options to eliminate a stone in the urinary tract.
Roughly, the most used methods are:
- Extracorporeal lithotripsy (ESWL) – a method where stones are broken by means of shock waves applied through the skin.
- Ureterolithotripsy – shock waves are applied directly to the stones, through an endoscope inserted through the urethra into the ureter.
- Percutaneous nephrolithotomy – a minor surgery where the endoscope is inserted through the skin to where the stone is.
- Conventional surgery – procedure where the kidney needs to be opened to remove the stones. Commonly used in complicated calculi, especially coral-like calculus.
Extracorporeal shock wave lithotripsy (ESWL) is currently the most used procedure, especially if the stone is inside the kidney or in the proximal ureter (initial part, close to the kidney).
In cases of very large stones, larger than 15 mm (1.5 cm), or if the stone is impacted in the lower half of the ureter, extracorporeal lithotripsy cannot be as effective. In these cases, ureterolithotripsy or percutaneous nephrolithotomy have better results.
Double J Catheter
After any manipulation of the ureter, it may present a degree of edema secondary to the inflammatory reaction, which in itself can obstruct the passage of urine and calculi that may still remain.
Therefore, it is customary to insert a catheter called a double-J, or pig’s tail (pig-tail in English), to ensure the permeability of the manipulated route.
The catheter has both ends in a shape similar to the letter J, hence its name. Double J has holes in its path that allow urine to flow
One end is inside the kidney and the other inside the bladder. Therefore, even if there is obstruction at any point in the ureter, regardless of the cause, the double-J guarantees the permeability of the urinary tract.
After placement of the double J, there may be lower back and abdominal pain, burning when urinating and bleeding in the urine for a few days. If there is fever, excruciating pain, or exuberant bleeding with clots, contact your urologist for re-evaluation.
The double-J catheter can remain in the ureter for 3 to 9 months depending on its diameter. In most cases, it is not necessary to keep the catheter for that long. When the urologist indicates the prolonged use of double-J, the ideal is that every 3 months the catheter is reassessed to make sure it is not obstructed.
Catheter removal is a simple procedure and is done endoscopically with a cystoscope. You enter the urethra with this endoscope and pull the catheter out. If there are no complications such as adhesions or double-J dislocations, removal is a quick procedure, and in most cases, painless.
Investigation of the composition of the calculus
Once the calculus problem is solved, either spontaneously or through medical intervention, the next step is to try to identify the stone’s composition so that strategies can be devised to prevent the appearance of new kidney stones.
If the patient manages to keep the discarded stone, its contents can be analyzed in a laboratory. But even if it is not possible to recover the expelled stone, a follow-up with a Nephrologist is indicated so that he, through the evaluation of the composition of his urine, can look for problems that facilitate the formation of calculi.
Patients who have excess calcium, oxalate, phosphorus, or uric acid in their urine are at increased risk of forming stones. On the other hand, lack of citrate in the urine or poorly diluted urine are also risk factors. Often, the correction of these changes in urine composition are enough to prevent the appearance of new stones.
The coralliform calculus is so named because it has the appearance of a coral. These are the largest stones and usually occur in patients with a urinary tract infection by a bacterium called Proteus .
This bacteria increases the pH of the urine and favors the precipitation of salts, especially struvite, composed of phosphate, ammonia and magnesium
The coralline calculus is so large that it is easily visualized on a simple abdominal radiograph. Due to its size and shape, the coralliform calculus cannot get out in the urine and a surgical procedure is always necessary for its removal.
If left untreated, this stone leads to recurrent urinary infections and scarring of the kidneys, which can lead to end-stage renal failure.
- Urolithiasis – European Association of Urology.
- Surgical Management of Stones: AUA/Endourology Society Guideline (2016) – American Urological Association.
- What are Kidney Stones? – American Urological Association.