Generality
The pH of the urine may vary within a fairly broad normal range. Unlike the sanguine one, for which oscillations of ± 0.4 points are already in itself a sign of serious pathologies, the pH of urine normally fluctuates between 4.6 and 8, in relation to the diet and the health of the organism. Outside of these limits, although with slight differences between the various analysis laboratories, the condition is considered pathological.
What's this
The pH is the measure of the acidity or alkalinity of a solution.
The pH scale varies from 0 to 14, so:
- Neutrality is indicated by 7;
- PH values below 7 indicate acidity;
- PH values above 7 indicate alkalinity / basicity.
The lower the pH value is compared to 7, the more the solution is acid; the higher this value is compared to 7, the more it is alkaline.
What does urine pH depend on?
The pH of urine reflects renal ability to maintain a normal concentration of hydrogen ions in plasma and extracellular fluids. This result is obtained mainly through the reabsorption of sodium and the secretion of hydrogen and ammonium ions by the renal tubules.
The most traditional and simple method for assessing the pH of urine is to soak a litmus paper in a fresh urine sample. In practice, a strip of paper containing a dye of natural origin is used, which gives it the ability to turn from light green (at neutral pH) to the various shades of red (in an acid environment, pH 8.0). Litmus paper is therefore an excellent pH indicator, which is established by comparing the color obtained with the relative chromatic scale of reference.
In the medical field, urinary pH is monitored in order to evaluate the existence of systemic acid / base disorders of metabolic or respiratory origin. Furthermore, it is important in the monitoring of all those patients who for certain reasons must maintain a specific pH of their urine. This is the case, for example, of people at risk of kidney stones, more likely when the urinary pH deviates significantly from the "ideal" value (6.0 / 7.0 depending on the authors). Acid urine is associated with cystine, xanthine and uric acid stones, while in the presence of basic urine the risk of renal calcium phosphate, calcium carbonate, magnesium phosphate and struvite concretions increases. Calcium oxalate stones develop most in neutral or alkaline urinary environments.
- In the presence of urolithiasis it is advisable to maintain the urinary pH between 6.5-6.8 to favor the dissolution of uric acid crystals. A daily water intake of 2.5-3 liters is also recommended to favor the dilution of urinary uric acid.
An acidification of urinary pH can help as a support to the pharmacological treatments against urinary infections *, while the maintenance of a basic pH is seen, especially by the lovers of alternative medicines, as a sort of "purification" of the organism.
Notwithstanding the importance of a diet rich in fruit and vegetables, exacerbating a certain aspect of one's diet by moving away from the concept of "varied and balanced" is always dangerous; we have seen, for example, how this practice can increase the risk of some types of kidney stones, but there are also other conditions (such as taking certain medicines, for example potassium-sparing diuretics) that support the danger of this approach dietary.
* Drugs such as streptomycin, neomycin and kanamycin are effective in treating urinary infections when urine pH is alkaline.
Why do you measure
The measurement of urinary pH provides indications regarding the patient's acid-base status, on which the good functionality of the whole organism depends.
Usually, urine pH is used to measure the presence of various diseases:
- Acid / base systemic disorders;
- Respiratory disorders;
- Metabolic problems;
- Urinary tract infections.
Moreover, for some categories of patients it is important to maintain stable urinary pH values during the therapies, in order to succeed them.
Urine is considered alkaline when the pH is greater than 7; this outcome is often found in cases of urinary tract infection. When the pH is less than 7, however, there may be problems like diarrhea or starvation. There is also an inverse relationship between urine pH and ketone levels (acetone) in urine.
Normal values
Normal pH values in urine are between 5.0 and 7.0 (also variable depending on the diet).
High Urine pH - Causes
Increased (alkaline) values of urine pH may be caused by:
- He retched;
- Acidosis of the renal tubules;
- Respiratory acidosis;
- Metabolic or respiratory alkalosis;
- bacteriuria;
- Urinary tract infections;
- Kidney failure;
- Pyloric obstruction;
- Fanconi syndrome;
A high pH in urine can also be determined by the use of some drugs, such as:
- Acetazolamide;
- amiloride;
- Antibiotics;
- Potassium citrate;
- Sodium bicarbonate.
Most fruits and vegetables make the urine more alkaline, so raise the pH.
Low Urine pH - Causes
Minute values (acids) of urine pH may be due to:
- Poorly controlled diabetes (diabetic ketoacidosis);
- Diarrhea;
- Severe dehydration;
- Emphysema;
- Metabolic acidosis;
- Phenylketonuria;
- Urinary tract infections;
- Renal tuberculosis;
- Respiratory diseases with insufficient elimination of carbon dioxide;
- Particularly prolonged fasting and starvation (the most extreme form of malnutrition).
A low pH in urine can also be determined by the use of some drugs, such as:
- Ammonium chloride;
- Ascorbic acid;
- Diazosside;
- Methenamine mandelate;
- Metolazone.
Currant juice, eggs, meat, pineapple juice and high-protein diets make urine more acidic, so they reduce the pH.
How to measure it
The most traditional and simple method for measuring the pH of urine involves the use of a litmus paper, which is immersed in the urine sample, strictly fresh. This strip of paper contains a dye of natural origin, which gives it the ability to turn from green (at neutral pH) to various shades of red (in an acid environment, pH 8.0).
The litmus paper is then compared with the relative chromatic scale of reference.
Preparation
- The urine pH should be evaluated on a strictly fresh urine sample; in the event that time passes between the collection of the same and the analysis, the sample must be properly stored in a refrigerator at a constant temperature.
- For the pH measurement it is necessary to collect a small amount of urine in a sterile container, after having carried out a thorough intimate hygiene and after letting go of the very first issue.
- The urine pH readings can vary substantially if the measurement is made in the morning, in the middle of the day or in the evening. In fact, when waking up, there are decidedly lower pH values.
Interpretation of Results
- A high urine pH (alkalinity) may be due to: vomiting, urinary tract infections (Proteus sp.), Renal failure, some diuretic therapies, renal tubular acidosis, gastric lavage and respiratory diseases characterized by hyperventilation (with excessive elimination of CO2 ).
- A reduced urine pH (acidity) may be due to poorly controlled diabetes (diabetic ketoacidosis), diarrhea, severe dehydration, emphysema, respiratory diseases with insufficient elimination of carbon dioxide, particularly prolonged fasting and starvation (the most extreme form of malnutrition).
As regards the influence of the diet on urinary pH, acid urine is typically present in diets rich in meat, especially if preserved, and alkaline urine in vegetarian or more generally diets rich in vegetables and fruit (with the exception of prunes and blueberries) . The topic, together with the physiological mechanisms responsible for the control of urinary and plasma pH, has been deepened in this article dedicated to the alkaline diet.
Finally, we emphasize that the urine pH is lower in the morning than in the evening, since during sleep the reduction in pulmonary ventilation causes respiratory acidosis; for this reason it is preferable to measure it especially when waking up.
There are also lower urinary pH values in fasting compared to post-prandial periods.
