Kidney stones are formed when substances that are normally dissolved in the urine become firm. Often, kidney stones do not produce symptoms. But especially larger crystals can cause colic and other ailments. What are possible causes? And which treatment makes sense?

The kidneys purify the body. They filter breakdown products, poisons and other unwanted substances out of the blood. From this "garbage" the kidneys form urine, which the body excretes via the bladder and the urethra.

Normally, these substances are dissolved in the urine. Under certain conditions, however, some of the substances may crystallize and accumulate as stones in the urinary tract. Depending on where they are deposited, it is called kidney stones, ureteral stones or bladder stones.

What are kidney stones?

Kidney stones (nephroliths: Greek nephrós = kidney, líthos = stone) are solid structures that form from normally dissolved in the urine substances. Their size can range from a few millimeters (about rice grain size ) to several centimeters. Most kidney stones occur on one side.

stone types
Kidney stones can be divided into different stone types depending on the composition :

Calcium oxalate stones make up about 80 percent of all urinary stones.
Uric acid stones (urate stones) (10%)
Magnesium-ammonium-phosphate stones (struvite stones) - also called infectious stones, as they are associated with a urinary tract infection, 5%
Calcium phosphate stones (5%)
rare stones (<1%) such as cystine stones and xanthine stones
Kidney stones: Symptoms usually appear late
Whether and what symptoms occur depends on the size and location of the kidney stones. Small kidney stones can go unnoticed through the ureter into the bladder and get out while urinating.

Larger kidney stones, on the other hand, can touch the wall of the ureter and even get stuck in it. This can cause violent spasms or labor-like, stinging pains (so-called ureter colic ). They usually start in the flank and radiate along the ureter into the lower abdomen.

Deep-seated kidney stones can even trigger pain radiating into the genitals ( scrotum or labia ). As the stone moves slowly through the urinary tract, pain also often moves with it.

In addition, if a kidney stone injures the wall of the ureter, bleeding may occur. When the stone passes into the urinary bladder and then into the urethra, there is often so much blood in the urine that it can be seen with the naked eye (so-called gross hematuria ).

Kidney stones: causes and development
Whether a human develops kidney stones depends primarily on the composition of his urine. The decisive factor is above all:

the amount of stone-forming substances in the urine,
the amount of so-called stone formation inhibitors (lat inhibitor = inhibitor) in urine and
the acidity of urine (pH).
Too high a concentration of stone-forming substances
If certain substances in the urine exceed a certain concentration, they become solid crystals. When, over time, layers of new layers are attached to the crystals on the onion-peel-like scale, kidney stones develop. The substances that can form kidney stones include:

Calcium,
Phosphate,
Oxalate (salt of oxalic acid),
Uric acid as well
Cystine.
Too few inhibitors
The urine of healthy people is sometimes supersaturated with one or some of the substances mentioned. They, too, form crystals - but the body normally excretes them unnoticed without forming kidney stones.

This is because the urine of healthy people contains substances such as citrate and magnesium, which inhibit the formation of stones. In contrast, people susceptible to kidney stones often have very low levels of such inhibitors in the urine.

Too high or too low acidity
Healthy is slightly acidic urine with a pH of 6. If the pH is lower than 5.5, the urine contains too much acid. People with acid urine often develop uric acid stones.

Urinary tract infections can cause the acidity of the urine to drop and the pH to rise. A pH above 7 favors phosphate-containing kidney stones.

What influences the composition of the urine?
Which substances accumulate in which concentration in the urine depends above all on the lifestyle, that is,

how much you drink,
how to eat,
if you move regularly and
whether you have certain pre-existing conditions such as chronic diarrhea, gout or diabetes.
If a man drinks too little liquid while eating and drinking, his kidneys can produce only a little urine. The water content of the urine decreases and the concentration of certain substances in the urine increases. Fluid loss through sweating (eg in hot climates) or diarrhea (watery stools) also increases the risk of kidney stones.

Wrong diet
If you eat a lot of salt, more calcium and less citrate get into the urine. Therefore, a high-salt diet increases the risk of calcium-containing kidney stones. Of course, these can also occur if you ingest too large amounts of calcium-rich foods. These include milk, cheese, and other dairy products.

A permanently to protein-rich diet (lots of meat and sausage products, especially organ meats) leads to an oversupply of certain substances in the blood (known. Purines), which breaks down the body to uric acid and thus eliminated in the urine. If the level of uric acid in the urine rises above a certain level, uric acid residues can form.

Metabolic diseases
High levels of calcium and phosphate in the blood can sometimes be attributed to parathyroid hyperfunction (hyperparathyroidism).

An excess of oxalic acid is sometimes the result of primary hyperoxaluria, a congenital enzyme disorder. The oxalic acid content in urine may also increase due to inflammatory bowel diseases such as ulcerative colitis (chronic colitis ) or Crohn's disease. Then doctors speak of secondary hyperoxaluria.

A high concentration of uric acid in the urine is sometimes related to diabetes. Why is not clear yet.

lack of exercise
People who move little often have an increased risk of kidney stones. If, for example, you are bedridden for a long time due to a serious illness, the body not only removes muscle tissue but also calcium from the bones. As a result, the concentration of calcium in the urine increases and kidney stones can form.

Kidney stones: diagnosis
If the patient complains of labor-like pain in the flanks, the doctor will consider kidney stones as a possible cause. To be able to make a diagnosis, he must first look at the kidneys. For this, he can make an ultrasound examination. If the results are ambiguous, he may additionally take CT images of the kidney.

In addition, the doctor examines the patient's urine. For example, he can determine whether the patient has an infection or whether his calcium or uric acid levels are elevated.

Kidney stones: treatment
Small kidney stones with a diameter of 5 millimeters usually separate the patients within one month by themselves. Therapy is then not necessary. Sometimes, however, it causes pain when a kidney stone passes through the ureter (so-called acute ureteral colic). In this case, the doctor may prescribe anti-inflammatory analgesics such as diclofenac.

If the stones are more than a centimeter in size or cause severe discomfort, they should be removed. This is especially advisable if:

the patient has severe pain despite medication,
the patient is also suffering from a urinary tract infection with fever and/or
a kidney stone completely blocks the urinary tract.
This is how kidney stones are removed
Only uric acid stones can sometimes be dissolved by medication. The patient should then drink a lot so that the kidneys form more urine, in which the uric acid can dissolve.

Other types of kidney stones cannot be eliminated medically. To remove them, the doctor may either smash them or surgically remove them.

How can kidney stones be smashed?
To smash kidney stones, no surgery is needed. The doctor can smash kidney stones from the outside with the aid of so-called extracorporeal shockwave lithotripsy (ESWL) . To do this, he applies a probe to the skin, which sends sound waves through the skin to the kidney. The sound waves shatter the kidney stones into small pieces. These then excrete the kidneys by itself with the urine.

During pregnancy or untreated urinary tract infection, this therapy should not be used.

When is an operation necessary?
For kidney stones with a diameter of 2 centimeters or more, a shock wave treatment is not enough. The resulting fragments would still be too large to be excreted by the kidneys.

Large kidney stones usually need to be removed. However, an open operation is rarely used today. As a rule, doctors use the following endoscopic procedures :

Ureterorenoscopy (URS): The doctor introduces an endoscope and fine instruments through the urethra into the ureter. The doctor uses a laser to crush the kidney stone. Then he removes the fragments with a stone basket. If the urinary tract is inflamed, this method is not recommended.
Percutaneous nephrolitholapaxy (PCNL): This procedure is performed under general anesthesia and is performed in the hospital. The doctor puts a small skin incision. Through the opening, he can insert the endoscope and surgical instruments directly into the renal pelvis or into the cavities of the kidney. Also, this treatment is not suitable during pregnancy and an untreated urinary tract infection.
Kidney stones: course
About 85 percent of the smaller urinary stones are eliminated by the body itself. This usually happens within a month. Nearly half of those affected do not develop kidney stones afterward.

It usually makes sense to remove larger kidney stones that the body does not excrete by itself. This is absolutely necessary if the stones close the urinary tract. Because then there is a risk that bacteria immigrate and cause infections of the urinary tract and kidneys.

Can you prevent kidney stones?
More than half of the patients repeatedly develop kidney stones. However, this can often be prevented with certain measures.

drinking water
Kidney stones are formed when the urine contains so much of certain substances that they do not dissolve anymore. By drinking a lot (at least 2.5 liters of unsweetened liquid daily), you can dilute the urine and thus reduce the risk of kidney stones.

Soft drinks such as cola, however, are not recommended because they contain phosphoric acid (usually referred to as additive E338). Physicians suggest that phosphoric acid favors the formation of kidney stones.

change nourishment
In addition, one can specifically prevent individual types of kidney stones. Because some of the stone-forming substances are found in different foods, it is possible to lower their urinary concentration through a controlled diet :

Those who have oxalate stones or calcium oxalate stones should avoid oxalate foods such as spinach, rhubarb, beetroot, green and black tea, and chocolate and cocoa. However, people should not give up calcium with these types of stones, since too little calcium in the diet causes more oxalate to enter the urine.
For calcium oxalate stones, it is also recommended to eat low salt and low animal protein.
In combination with gout and diabetes, uric acid stones are common. Uric acid is produced by the breakdown of so-called purines, which are contained in animal offal (liver, kidneys, heart, tongue), meat and sausages, oil sardines and legumes. Maybe a low-purine diet helps to prevent uric acid stones. So far there is no scientific evidence for it.
drugs
Patients at increased risk for certain types of kidney stones may prescribe medication to the doctor:

Calcium citrate is suitable for the prevention of kidney stones of calcium, uric acid, and cystine. It reduces the acidity of the urine. The less acidic the urine, the more salts can dissolve in it.
Allopurinol lowers the uric acid level in the urine and thus counteracts uric acid stones. Studies have shown that it can also protect against calcium stones.
Thiazide diuretics reduce the risk of calcium oxalate stones and calcium phosphate stones by causing less calcium to get from the blood into the urine.