What is the pH value?
The pH value is defined by the amount of positively charged hydrogen ions (H+ ions) in a solution. Strictly speaking, it corresponds to the negative decadic logarithm of the concentration of H+ ions. It can be determined for any solution and provides information about how acidic it is.
pH value: acidic or basic?
An acidic pH in the blood is said to exist at values of less than 7.36. When the blood has such a low pH, the doctor speaks of hyperacidity of the blood (acidosis). A pH value of 7.44 or more is considered alkaline. Then an alkalosis is present. The reference range of the pH value in the blood is therefore very narrow and allows only minimal deviations.
The control of the pH value
It is important that the pH remains neutral – otherwise alkalosis or acidosis will occur, both of which can be life-threatening. To prevent this, the body has various buffer systems.
Other systems are protein and phosphate buffer systems.
When do you determine the pH value?
The doctor determines the pH value in the blood when a disorder of the acid-base balance is suspected. The blood sample can come from either a vein or an artery. Indications of a pH change include headaches, tremors, delirium and clouding of consciousness.
In clinical practice, the physician usually determines the blood pH during a blood gas analysis. It is useful and necessary in:
- pulmonary dysfunction, respiratory disorders
- severe circulatory disorders (shock)
- metabolic derailments
- loss of endogenous acids or bases (for example in case of vomiting or diarrhea)
- poisoning
- kidney weakness (renal insufficiency)
- high fever
- sepsis (“blood poisoning”)
pH value: Table with normal values
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Normal value |
|
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pH value: blood |
Adults and children: 7.36 to 7.44 Newborns: 7.2 to 7.38 |
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pH value: gastric juice |
2,0 |
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pH value: Urine |
5.0 to 7.0 |
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pH value: Saliva |
7.0 to 7.1 |
When is the pH value in the blood too low?
Respiratory acidosis occurs when there is a lot of carbon dioxide (CO2) in the body. This happens, for example, in patients suffering from chronic lung diseases.
In metabolic acidosis, a lowered bicarbonate concentration is the problem. Possible causes are:
- Insulin deficiency in diabetes mellitus
- Vitamin B1 deficiency
- Shock
- Alcoholism
- Poisoning
- diarrhea or abuse of laxatives
When is the pH in the blood too high?
When the pH is elevated, it is called alkalosis. It means that the pH is alkaline. A variation up to 7.5 denotes mild alkalosis. A pH of 7.6 or higher indicates severe, life-threatening alkalosis. Again, the metabolic form is distinguished from the respiratory form:
Metabolic alkalosis results from loss of acids or supply of bases. Acid loss can result, for example, from prolonged vomiting or treatment with diuretics (dehydrating agents). Excessive base intake consists of the excessive administration of basic (alkaline) substances such as citrate or sodium bicarbonate.
What to do in case of altered blood pH?
The therapy for pH changes depends on the cause. Therefore, the physician must first determine it. To determine the mechanism of the pH disturbance, he assesses the values of bicarbonate and carbon dioxide measured in the blood gas analysis. If the pH is severely altered, i.e., if there is a severe derailment, the physician must care for the patient in the intensive care unit.
pH value: urine
Urine pH can be determined quite easily with a conventional urine test strip. Altered values can indicate a disease, for example a urinary tract infection.
pH value (urine): Acidosis
If the pH value in the urine is lower than normal, this is referred to as acidosis or acidotic urine. It occurs in, among others:
- high fever
- gout
- metabolic or respiratory acidosis
- a diet very rich in meat
- taking certain medications
pH (urine): alkalinization
pH value (urine): Pregnancy
Pregnant women have an increased risk of urinary tract infections. This is one of the reasons why the urine is tested with a test strip during regular prenatal examinations. If the urine pH is conspicuous, the doctor can immediately initiate pathogen-specific treatment, for example with antibiotics.
