Urine ph

The pH value represents the negative decadic logarithm of the hydrogen ion concentration.

In an aqueous solution, it indicates the proportion of free H+ ions in the form of H 3 O+ ions.

A solution with a pH value < 7 is called "acidic" and with a pH value > 7 "alkaline".

(Müller 2005).

The pH value of fresh urine normally lies between 4.6 - 8.0 (Herold 2021). It depends on food and is therefore subject to large daily fluctuations (Manski 2019).

The pH- value is usually measured with a strip test, which has a pH-sensitive dye in the range of pH 5 - pH 9 (Eichenauer 2013). If the pH value is outside this range, the measurement is taken with the pH meter.

The pH value of the urine gives indications of disturbances in the acid-base balance.

(Kuhlmann 2015)

1. alkaline urine pH values

They can occur with:

• vegetarian diet
• Alkalosis
• long storage of urine (due to bacterial overgrowth [Keller 2010]).

(Herold 2021)

• Drug treatment with e.g. potassium citrate, which is used therapeutically (Kuhlmann 2015).
• Urinary tract infections (Hegele 2015) with urease-producing bacteria such as Proteus, Klebsiellen, Pseudomonas, Staphylokokken etc. (Risler 2008)
• Increased excretion of Na+, K+ and bicarbonate (at pH- values > 7, urine always contains high concentrations of bicarbonate).

(Kuhlmann 2015)

2. acidic urine pH values

They are found with:

• Meat-rich diet
• Acidosis (especially in diabetic ketoacidosis [Luppa 2017])

(Herold 2021)

• in a state of fasting (urine pH < 5.0)
• Diarrhea
• high fever

(Luppa 2017)

• insufficient supply of NH3 into the medullary renal interstitium in the context of a disturbance of the acid-base balance

(Kuhlmann 2015)

At pH values < 6, the urine no longer contains bicarbonate (Kuhlmann 2015)

Nephrolithiasis

Clinically, the pH- value of the urine plays a major role in the formation of certain forms of kidney stones (seetypes of urinary stones).

(Kuhlmann 2015)

In the case of a urinary tract infection, for example, gram-negative bacteria (such as Proteus, Klebsiae, Pseudomonas - except E. coli) cause a change in the pH value, through which the urea is split into NH3 and CO2, which in turn increases the pH value of the urine. This leads to a change in ion solubility and thus to the formation of kidney stones.

Nephrolithiasis and urinary tract infection favor each other.

(Herold 2020)

Kidney stone formation

• Calcium stones

In calcium stones, the pH- value of the urine plays a major role: calcium- oxalate stones form at low pH, calcium- phosphate stones at high pH (Kuhlmann 2015).

• Ammonium-urate stones

These form preferentially in a pH- range of > 6.5.

(Seitz 2018)

• Dahllite / carbonate apatite stones.

They occur preferentially at high urine pH values of > 6.8 .

(Seitz 2018)

• Pure uric acid stones

The pH value in the urine is low in pure uric acid stones, since uric acid crystallizes at acidic pH values. In an alkaline environment, however, uric acid returns to solution. This principle is used therapeutically by raising the pH value. Even already existing stones can be dissolved again (Wendt-Nordahl 2014 / Seitz 2018).

Solubilities

The pH-value also has an influence on the solubility of certain substances, e.g.

• Uric acid

At a urine pH of 6.5, the predominant number of uric acid ions is present as sodium urate and uric acid shows a high solubility of up to 1,000 mg / l.

At a pH of 5.35, 50% of the uric acid is dissociated.

From a pH ≤ 4.5, only undissociated uric acid is found in urine.

(Kuhlmann 2015)

• Ammonium-urate

Ammonium urate, on the other hand, only crystallizes at high pH values. This is used therapeutically for urate stones by acidifying the urine (Seitz 2018).

• Potassium urate

Potassium urate, like sodium urate, is highly soluble at a pH of 5.35.

(Kuhlmann 2015)

• Calcium phosphate

Calcium phosphate is soluble at pH- values of < 6.7. At a pH > 6.7, the solubility decreases (Klinke 2005).

• Cystine

At pH- values of ≥ 7.5, there is good solubility of cystine, which is also used medicinally for cystine stones (Kuhlmann 2015).

Mismeasurements

The pH- value plays a role in the detection of certain substances in urine.

For example, a pH value of > 7.0 can indicate false positive values for albumin (Kasper 2015).

Therapy

In the case of certain types of urinary calculi, the possibility of alkalinising or acidifying the urine with medication is used to prevent recurrences or to keep them as low as possible.

1. Eichenauer R H et al (2013) Clinician's guide to urology. Urban und Fischer Verlag 2.4.1
2. Hegele A et al (2015) Urology: intensive course for continuing education. Thieme Verlag 35
3. Herold G et al (2021) Internal medicine. Herold Publishers 600
4. Kasper D L et al (2015) Harrison's Principles of Internal Medicine. Mc Graw Hill Education 293
5. Keller C K et al (2010) Practice of nephrology. Springer Verlag 19
6. Klinke R et al (2005) Physiology. Georg Thieme Publishers 369
7. Kuhlmann U et al. (2015) Nephrology: pathophysiology - clinic - renal replacement procedures. Thieme Verlag 41, 304, 596 - 599
8. Luppa P B et al (2017) POCT - patient-oriented laboratory diagnostics. Springer Verlag 190
9. Manski D (2019) The urology textbook. Dirk Manski Publishers 74
10. Müller O (2005) Chemistry simply and understandably: an easy-to-understand introduction to the fundamentals of chemistry for high school students and for students with a minor in chemistry. Books on Demand GmbH Publisher 171
11. Risler T et al (2008) Specialist nephrology Urban and Fischer.
12. Seitz C et al. (2018) S2k guideline on the diagnosis, therapy and metaphylaxis of urolithiasis (AWMF registry number 043 - 025).
13. Wendt- Nordahl G (2014) Metabolic diagnosis and prevention of urolithiasis. The Urology 1 - 21 DOI 10.1007/978-3-642-41168-7_37-1.