PH value

and Martina Feichter, medical editor and biologist

Martina Feichter studied biology with an elective subject pharmacy in Innsbruck and also immersed herself in the world of medicinal plants. From there it was not far to other medical topics that still captivate her to this day. She trained as a journalist at the Axel Springer Academy in Hamburg and has been working for since 2007 - first as an editor and since 2012 as a freelance writer.

More about the experts All content is checked by medical journalists.

The pH value provides information about the ratio of acids and bases in a solution. It depends on the amount of hydrogen ions (H + ions) and can be determined for the blood, urine or saliva, for example. Here you can read everything you need to know about the pH value: definition, regulation and possible causes for shifts in the degree of acidity.

What is the pH?

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 each solution and provides information about how acidic it is.

pH value: acidic or basic?

An acidic pH in the blood is when the pH is less than 7.36. If the blood has such a low pH value, the doctor speaks of over-acidification of the blood (acidosis). A pH of 7.44 or more is considered basic. Then there is an alkalosis. The reference range for the pH value in the blood is therefore very narrow and only allows minimal deviations.

Control of pH

It is important that the pH value remains neutral - otherwise alkalosis or acidosis will occur, both of which can be life-threatening. To prevent this, the body has various buffer systems.

The most important buffer system is the bicarbonate system: Here the acid-base balance is regulated by carbon dioxide (CO2) and bicarbonate (HCO3-). If there is an excess of acids, the negatively charged bicarbonate absorbs positively charged particles, which are then exhaled as carbon dioxide. If there are too many basic substances, on the other hand, less carbon dioxide is exhaled.

Other systems are protein and phosphate buffer systems.

When do you determine the pH value?

The doctor determines the pH value in the blood if a disturbance in the acid-base balance is suspected. The blood sample can come from either a vein or an artery. Headaches, tremors, delirium and impaired consciousness are indications of a change in pH.

In everyday clinical practice, the doctor usually determines the blood pH with a blood gas analysis. It is useful and necessary for:

• Pulmonary dysfunction, breathing disorders
• severe circulatory disorders (shock)
• Metabolic imbalances
• Loss of endogenous acids or bases (for example, when vomiting or diarrhea)
• Poisoning
• Kidney failure (renal failure)
• high fever
• Sepsis ("blood poisoning")

pH value: table with normal values

	Normal value
pH value: blood	Adults and children: 7.36 to 7.44 Newborns: 7.2 to 7.38
pH value: gastric juice	2,0
pH value: urine	5.0 to 7.0
pH value: saliva	7.0 to 7.1

When is the pH in the blood too low?

A low pH indicates that the solution is acidic. This is called acidosis. If the value drops to a maximum of 7.3, one speaks of a slight acidosis; Values ​​below 7.1, on the other hand, are life-threatening. Depending on the mechanism of development, the doctor differentiates respiratory from metabolic acidosis:

Respiratory acidosis occurs when there is a lot of carbon dioxide (CO2) in the body. This happens, for example, with patients who suffer from chronic lung diseases.

In metabolic acidosis, decreased bicarbonate levels are the problem. Possible causes for this are:

• Insulin deficiency in diabetes mellitus
• Vitamin B1 deficiency
• shock
• alcoholism
• Poisoning
• Diarrhea or laxative abuse

When is the pH in the blood too high?

If the pH value is increased, this is called alkalosis. It means the pH is basic. A deviation of up to 7.5 indicates a slight alkalosis. A severe, life-threatening alkalosis is present at a pH value of 7.6 or more. Here, too, a distinction is made between the metabolic and the respiratory form:

Metabolic alkalosis is caused by the loss of acids or the intake of bases. Loss of acid can result, for example, from prolonged vomiting or treatment with diuretics. An excessive base intake consists in the excessive administration of basic (alkaline) substances such as citrate or sodium hydrogen carbonate.

Respiratory alkalosis, on the other hand, is often based on hyperventilation, i.e. breathing that is too fast and too deep. Other possible causes are pulmonary fibrosis, pneumonia, and pulmonary embolism.

What to do if the blood pH value changes?

Therapy for pH changes depends on the cause. Therefore, the doctor must first determine this. In order 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 value has changed significantly, i.e. if there is a serious derailment, the doctor has to look after the patient in the intensive care unit.

pH value: urine

The pH value in the urine can be easily determined with a conventional urine test strip. Changed values ​​can indicate an illness, for example a urinary tract infection.

pH value (urine): acidification

If the pH value in the urine is lower than normal, this is referred to as hyperacidity or acidotic urine. Among other things, he appears at:

• high fever
• gout
• metabolic or respiratory acidosis
• very meat-rich diet
• Taking certain medications

pH value (urine): alkalization

If the pH value (urine) is too high, there may be a urinary tract infection with certain pathogens (such as Proteus mirabilis). However, alkaline urine is not always indicative of an infection: The test field shows an increased pH even with a diet rich in vegetables or if the urine sample has been standing too long before the pH determination.

pH (urine): pregnancy

Pregnant women are at increased risk of urinary tract infections. This is one of the reasons why the urine is checked with a test strip during regular prenatal check-ups. If the urinary pH value is abnormal, the doctor can immediately initiate a pathogen-specific treatment, for example with antibiotics.

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