Urine is a solution containing various substances, such as calcium, phosphate, oxalate, cystine, and uric acid, among others, which are normally in a state of equilibrium so that they can be easily absorbed, utilized by the body, and easily eliminated through the urinary tract.
However, if the urine is very concentrated or if there is something that alters the concentration of its constituent substances, meaning this equilibrium is disrupted, it can lead to the formation of crystals. When these crystals get stuck in the renal tissue and grow in size, we then refer to them as kidney stones.
Thus, the formation of stones will depend on the action of various factors (presence of substances that favor crystal formation, absence of crystallization inhibitors, urinary tract infections, urinary flow, urine pH, metabolic disorders, lifestyle, diet...) on the equilibrium of the urinary flow's composition. There are five main groups of kidney stones:
- Uric acid: formed by an excess of protein in the urine and urinary acidity below pH 5.5.
- Calcium phosphate: formed mainly by a high concentration of calcium in the urine and generally alkaline urine with pH values above 6.2.
- Calcium oxalate: composed of calcium and oxalate, their appearance depends on a previous crystalline formation, commonly uric acid or calcium phosphate. This is the most common type of kidney stone.
- Struvite: formed by phosphate, calcium, and magnesium. They are directly related to the presence of bacteria in a urinary tract infection, which will favor an increase in urinary pH above 6.2.
- Cystine: formed by an excess of cystine in the urine. This is the least common type of kidney stone but has a higher frequency of formation. Its prevention is complex; among other measures, a very strict control of urinary pH is recommended to maintain it at alkaline levels above 7.5.
One of the factors most related to the formation of kidney stones is changes in the level of urinary pH because they influence the solubility and crystallization of the different components present in urine.
If the urine is alkaline (with a pH value above 6.2), present, for example, in cases of urinary tract infection, it will promote the formation of phosphate stones (calcium or struvite) and calcium oxalate stones. Conversely, if the urine contains a high level of acidity (with a pH value below 5.5), it will favor the appearance of uric acid, cystine, and also calcium oxalate stones.
To prevent their initial formation or recurrence (known as relapse), it is recommended to maintain very strict control of urinary pH to keep it at optimal safety levels, which would be between 5.5 and 6.2. For this, alternative treatments can be used, including food supplements that promote an adequate acid-base balance of the urine, and these can be monitored with the help of medical devices for measuring urine pH with the aim of properly tracking urinary pH.
