The pH of blood refers to how acidic it is. Changes to blood pH can signal underlying medical issues, including metabolic acidosis, respiratory acidosis, metabolic alkalosis, and respiratory alkalosis.
The pH scale, otherwise known as the acid-base scale, runs from 0 to 14. It measures how acidic a solution of a substance in water is. For example, pure water has a pH of 7.
Solutions with a low pH have a high concentration of hydrogen ions and are acidic. Solutions with a high pH have a lower concentration of hydrogen ions and are alkaline, or basic.
The pH scale is a compact scale, and small changes in pH represent big leaps in acidity.
This article will look at what the normal pH level of blood is and what can cause the pH level to move outside of this range. It will also examine what can happen to the body if blood pH levels go above or below the normal range.
The pH of blood in the arteries should be between 7.35 and 7.45 for the body’s metabolic processes and other systems to work well. These processes produce acids, so the body has a complex system of feedback and regulation to maintain healthy pH levels.
Much of the acid made in the body is carbonic acid. This forms when carbon dioxide combines with water. Carbon dioxide occurs within the tissues of the body due to the process of respiration.
The lungs and the kidneys are the two main organs that regulate the pH of the blood, often at the same time. There are also chemical buffering mechanisms throughout the body’s cells.
The lungs can help regulate blood pH rapidly through the process of exhaling carbon dioxide, sometimes producing changes within seconds. For example, when someone exercises, they produce more carbon dioxide, so they breathe faster to prevent the blood from becoming too acidic.
The kidneys regulate the pH of the blood by excreting acids in urine. They also produce and regulate bicarbonate, which increases blood pH. These changes take longer than those that occur due to breathing, potentially taking hours or days.
Certain situations and medical conditions can mean that the body is unable to keep blood pH within the healthy range.
The pH of the blood can change in both directions.
Acidosis occurs when the blood is too acidic, with a pH below 7.35. Alkalosis occurs when the blood is not acidic enough, with a pH above 7.45.
There are four main ways in which blood pH can change:
- Metabolic acidosis: This occurs due to reduced bicarbonate or increased acid levels.
- Respiratory acidosis: This occurs when the body removes less carbon dioxide than usual.
- Metabolic alkalosis: This occurs due to increased bicarbonate or reduced acid levels.
- Respiratory alkalosis: This occurs when the body removes more carbon dioxide than usual.
To restore blood pH levels to a healthy range, it is important to identify and treat the underlying issue that has caused the change.
Metabolic changes in blood pH can occur as a result of kidney conditions or problems. Respiratory changes relate to how the lungs are working.
When a change happens in one direction, there are mechanisms to move the acid-base balance the other way. For example, if a person has respiratory acidosis, there should be a metabolic response from the kidneys to reset the balance.
If the body does not reset the pH balance, it can lead to more severe illness. For example, this can happen if the level of acidosis is too serious, or if the person’s kidneys are not working well.
Depending on the cause, changes in blood pH can be either long lasting or brief.
The sections below will look at the specific causes of each type of change to blood pH.
Metabolic acidosis
Metabolic acidosis can occur due to:
- kidney damage that leads to urea and other waste products building up in the blood
- strenuous exercise, which produces lactic acid
- consuming certain substances, such as aspirin, methanol, or paraldehyde
- losing bicarbonate from the body, such as during chronic diarrhea
- infection
- an excess of acids called ketones in the blood
Ketoacidosis typically occurs in people with diabetes or due to alcohol misuse.
Learn more about diabetic ketoacidosis here.
Respiratory acidosis
Respiratory acidosis occurs due to conditions that make breathing difficult. These include:
- lung conditions, such as pneumonia or chronic obstructive pulmonary disease
- congestive heart failure
- severe obesity
myasthenia gravis Guillain-Barre syndrome - brain injury
Using drugs such as opiates can also lead to respiratory acidosis.
Metabolic alkalosis
Some causes of metabolic alkalosis include:
- excess consumption of bicarbonate, antacids, or citrate
- Cushing’s disease, wherein there is too much of the hormone cortisol in the blood
- prolonged vomiting or serious dehydration
- an excess of fluid in the body
- taking too many laxatives
- some diuretics, which are medications that help the body get rid of excess water or salt
Respiratory alkalosis
Respiratory alkalosis often occurs due to situations or conditions that make people breathe quicker or deeper than usual. These include:
- shock, fear, or panic
- high temperature
- serious infection
- some lung conditions, such as pneumonia
- pulmonary embolism
- liver failure
- aspirin overdose, as the body overcompensates for the high acid levels this causes
If a person’s blood pH moves outside of the healthy range, they can begin to experience certain symptoms.
The symptoms they experience will depend on whether their blood has become more acidic or is no longer acidic enough.
Some symptoms of acidosis include:
- headache
- confusion
- tiredness
- lethargy and sleepiness
- coughing and shortness of breath
- an uneven or increased heart rate
- stomach upset or feeling sick
- muscle seizures or weakness
- unconsciousness and coma
Symptoms of alkalosis include:
- confusion and lightheadedness
- shaky hands
- numbness or tingling in the feet, hands, or face
- muscle twitches or spasms
- vomiting or nausea
- coma
There are two main types of tests that doctors can use to find out the pH of someone’s blood: arterial blood gas testing and electrolyte testing.
Knowing the pH of a person’s blood can help a doctor find out if that person has an acid-base disorder.
Doctors can also use these tests to monitor blood pH levels, establish and treat any underlying causes, and help care for people who are critically ill.
Arterial blood gas tests often take place in a hospital. They measure the acidity, oxygen, and carbon dioxide levels of the blood. A doctor will remove a small amount of blood, often from the wrist. They will then send this sample to a laboratory for analysis.
Electrolyte tests may be a part of routine care, or a doctor may perform them when a person becomes seriously ill. The test measures the levels of salts and minerals, such as bicarbonate, that are present in the blood. The doctor will usually need to take blood from a vein in the arm.
The results of these tests can help a doctor determine what is causing certain symptoms and whether or not the body’s regulatory systems are working correctly.
The pH of blood refers to how acidic it is.
The typical pH for blood in the arteries is 7.35 to 7.45. A complex set of mechanisms and feedback loops help regulate blood pH and keep the body working properly.
When the pH of the blood changes, it can indicate an underlying health concern that needs addressing. A doctor can use arterial blood gas and electrolyte tests to identify when this happens and make appropriate treatment recommendations.