What are Acidosis and Alkalosis?

Acidosis and alkalosis are conditions in which there is a disturbance in the pH balance (acid-base balance) of the body. Acidosis is a condition in which the bodily fluids become too acidic, with an abnormally low pH level. In alkalosis, the opposite is true: the fluids of the body are too alkaline (high in pH).

Acid-Base Balance in the Body

pH is a way of measuring the acidity or alkalinity of a fluid, on a scale from 1 to 14. A pH of 7 is considered neutral, while 1 is extremely acidic, and 14 is extremely alkaline, which is sometimes called “basic”. Normally, the pH of the human body is around 7.4, which is slightly higher than the chemically-neutral pH of 7. This slightly alkaline pH is ideal for many crucial processes that take place continually in the human body.

For instance, normal pH and proper acid-base balance enables the right amount of oxygen to enter and circulate in the blood, moving oxygen to all the cells and tissues of the body. Proteins, including enzymes, which speed up many chemical actions in the body, can’t function normally if body fluids are too acidic.


Acidosis occurs when bodily fluids contain too much acid. This results in a decrease in blood pH, since lower numbers represent more acidic substances. The blood is considered to be abnormally acidic (high in acid) when its pH is lower than 7.35.

Mild acidosis may be present without causing symptoms. In some cases, especially in seriously ill people, it can worsen if it is not diagnosed and treated. Acidosis can sometimes lead to serious physical effects, such a:

  • Hyperventilation (breathing abnormally fast or deeply)
  • Impaired heart function
  • Low blood pressure
  • Coma


Alkalosis is a condition in which the blood has too little acid, making it too alkaline or basic, which is another term for alkaline. This results in a higher blood pH, as higher numbers represent more alkaline substances. The blood is considered to be abnormally alkaline when its pH is above 7.45.

Mild, longstanding (chronic) alkalosis may occur without noticeable symptoms. Alkalosis that causes severe or rapid pH changes is more likely to cause symptoms that can include:

  • Dizziness or lightheadedness
  • Numbness of the hands and feet
  • Confusion
  • Nausea or vomiting
  • Muscle twitching or spasms
  • Low levels of oxygen in the blood
  • Seizures
  • Losing consciousness or being nearly unconscious

Staying in Balance

The normal pH of the human body ranges from 7.35 to 7.45, with 7.4 being average.

The body constantly engages in a number of activities to maintain pH within this narrow range. Under normal circumstances, the level of acids and bases in the body may rise and fall, as more acids and bases are produced or taken in. Processes in the body are always at work to adjust for these changes and keep the acid-base balance within the normal range.

Acid Buildup

Our bodies constantly produce acids during the normal processes of metabolism. Metabolism means all of the chemical and physical processes that our bodies use to generate energy and to produce substances necessary to maintain life. For example, our bodies convert nutrients in our food like fats, carbohydrates, and proteins into energy. The processes of metabolism normally generate large quantities of acids during these ongoing activities.

Most of the acid in our bodies is carbonic acid. The metabolism of fats and carbohydrates generates carbon dioxide which combines with water in the body to form carbonic acid. Other acids produced by the body include:

  • Lactic acid: This acid is mainly produced in muscle cells and red blood cells when the body metabolizes carbohydrates and oxygen levels are low, such as during intense exercise.
  • Ketoacids or ketones: These acids are formed by the breakdown of fats when the body’s main source of energy, glucose (sugar), is in short supply or when there is a lack of insulin, which is necessary for using glucose for energy.

Neutralizing and Removing Acids

Specialized cells in the brain and blood vessels sense the body’s acidity, and control processes that neutralize and remove acids. This feedback loop is essential to maintaining the body’s acid-base balance. Maintaining balance is crucial because even small changes can severely affect many organs and disrupt the way the cells of the body function.

The different mechanisms that the body uses to continually neutralize and remove acids and maintain pH balance include:

  • Breathing out carbon dioxide, which reduces acid in the body
  • Release of acid in urine
  • Regulating body pH through chemical buffering. Circulating weak acids and weak bases in the blood guard against abrupt changes in acidity and alkalinity.

How the Body Maintains Acid-Base Balance

The body automatically adjusts when it notices an imbalance in pH. The mechanisms it uses push the acid-base balance back toward the ideal pH range. The main organs involved in these processes are the lungs and the kidneys.

Lung Functions that Correct Imbalances

The lungs respiratory system responds to changes in acid-base balance caused by the body’s metabolic processes. Carbon dioxide, when combined with water, forms an acid (carbonic acid).   When you breathe out, carbon dioxide is removed from your body into the environment and your body removes acids that have been produced by metabolism. Your respiratory system automatically adjusts your breathing rate and the amount of air that moves out of the lungs. This ensures you exhale the right amount of carbon dioxide based on how much acid your tissues are producing.

For example, in diabetic ketoacidosis, low levels of insulin force the body to break down fats for energy use, in place of using glucose that requires insulin.  Breakdown of fat produces excess ketoacids, which lower the body’s pH. The breathing rate increases to get rid of carbon dioxide. When carbon dioxide is removed from the body at a faster rate, the level of acid in the body drops, and the pH starts to return toward the normal range.

The lungs also can also adjust when blood pH is too high. For example, if someone loses stomach acid due to vomiting, the blood pH can rise.  The breathing rate will slow and less carbon dioxide will be removed through breathing. This drives the body’s pH lower, toward the normal range.

Kidney Functions that Correct Imbalances

Your kidneys also play a critical role in maintaining your body’s pH. Generally, the kidneys respond with acid-base imbalances from conditions that affect the lungs.

The kidneys help maintain normal pH balance by increasing the amount of acid released in the urine when the body’s pH level is too low (acidic), and retaining bicarbonate, which is a base (alkaline substance). This drives the pH higher toward the normal range.

Conversely, when the body’s pH is too high (alkaline), the kidneys increase the amount bicarbonate released in the urine, and retain acid to lower the pH back toward the normal range.

The pH of urine shifts up or down as the kidneys adjust to blood acidity or alkalinity.

How Things Can Go Wrong

Although the body can generally maintain pH balance, some conditions can overwhelm the body’s ability to react to an imbalance. Acid-base imbalances can also occur when lung or kidney disorders affect the ability of these organs to control for pH imbalances.

Metabolic vs Respiratory Acidosis and Alkalosis

Acidosis and alkalosis are categorized according to whether they are caused by metabolic (related to basic bodily processes) versus respiratory (lung) problems. Understanding and determining the cause of the imbalance is important in helping to guide treatment of the pH imbalance.

The categories of acidosis are:

  • Metabolic acidosis: Metabolic acidosis occurs when too much acid is produced by the body, or too much bicarbonate, which is a base (alkali), is lost. Also, taking in certain substances or poisons that are acidic or become acidic in the body can overwhelm the body’s mechanisms and cause metabolic acidosis.
  • Respiratory acidosis: Respiratory acidosis occurs when lung or breathing disorders affect the body’s ability to breathe out carbon dioxide, leading to too much acid in the body.

The categories of alkalosis are:

  • Metabolic alkalosis: Metabolic alkalosis may be caused by losing too much acid from the body, or by having too much bicarbonate.
  • Respiratory alkalosis: Respiratory alkalosis can happen when there is too little carbon dioxide in the blood due to the lungs breathing out too much carbon dioxide. This may be due to hyperventilating, which is breathing abnormally fast, or conditions that cause shortness of breath.

The following table summarizes how the body works to adjust for acid-base imbalances:

Common causes of acidosis

The table below provides examples of common causes of acidosis:

Common causes of alkalosis

The table below provides examples of common causes of alkalosis:

Mixed acid-base imbalances

More than one acid-base imbalance can occur at the same time. This is called a mixed acid-base disorder or a complex acid-base disturbance. Mixed disorders happen when a patient has a condition that causes one type of imbalance then a second type of imbalance occurs.

For example, a patient with an alcohol abuse disorder may develop ketoacidosis due to alcohol misuse and metabolic alkalosis due to vomiting with loss of stomach acid. The ketoacidosis increases the acidity of body fluids at the same time the loss of stomach acid decreases acidity.

Another example of a mixed acid-base disorder may occur due to aspirin poisoning. Aspirin triggers increased breathing, which can lead to respiratory alkalosis due to hyperventilating. At the same time, aspirin is an acid, and large doses often cause metabolic acidosis.

Mixed acid-base disturbances may result in misleading test results that seem normal. Health care providers must carefully review laboratory test results to determine whether a single or mixed acid-base imbalance is present.

Testing for Acidosis and Alkalosis

When an acid-base imbalance is suspected, your health care provider will evaluate your vital signs, including blood pressure, breath rate, pulse, and temperature, and order tests to help diagnose or rule it out. If acidosis or alkalosis is detected, you may also have additional tests to determine its cause. Some people may have testing for acidosis or alkalosis to follow up on abnormal results on a common screening test, such as a complete metabolic panel (CMP).

Main tests

Diagnosis is typically based on the results of the following tests:

  • Blood gases: Blood gases are a group of tests performed on a blood sample that is usually collected from an artery, instead of a vein. Arteries are the blood vessels which carry blood from the heart to the rest of the body. Measurements of blood pH from an artery generally better reflect what is going on in the body than blood from a vein. Blood gases provide measurements that are important for the diagnosis of acidosis and alkalosis:
    • Blood pH
    • Carbon dioxide level, also called partial pressure of CO2, PaCO2 or PCO2
    • Oxygen level, also called partial pressure of O2, PaO2 or P02
    • Oxygen saturation, also called O2 Sat: determines oxygen levels based on measuring levels of hemoglobin. Hemoglobin is the protein in red blood cells that is responsible for carrying oxygen throughout the body.
    • Bicarbonate
  • Electrolytes and anion gap: These tests measure minerals in the blood, including sodium, potassium, chloride, and bicarbonate.Your health care team can use the results of this test to calculate your anion gap, which helps them narrow down the cause of acidosis and distinguish between anion-gap and non-anion-gap metabolic acidosis. Electrolytes may be measured by themselves, or as part of a Basic Metabolic Panel (BMP) or a Comprehensive Metabolic Panel (CMP).

Understanding acidosis and alkalosis test results

Blood gas results are interpreted in the context of your symptoms and history, as well as results from other tests performed at the same time.

Examples of test results associated with the four main acidosis and alkalosis conditions are provided in this table.

Additional testing

Additional testing may be done to understand the cause of acidosis or alkalosis. This is important because treatment typically is directed at the underlying cause. Testing may include one or more of the following, depending on the suspected cause:

Non-lab tests

Patients who are undergoing evaluation for acidosis and alkalosis may also have some of the following non-lab tests performed to determine what might be the underlying cause:

Treatment of Acidosis and Alkalosis

Treatment of both acidosis and alkalosis is almost always directed at reversing the cause of the disorder. It is rare for alkaline or acid substances to be given to restore balance.

Treatment of acidosis

How acidosis is treated will depend on what is causing it. For example, in metabolic acidosis caused by untreated diabetes, therapy may be directed at controlling blood sugar with insulin. If acidosis is caused by breathing problems, treatment aims at improving lung function. If breathing is severely impaired, mechanical ventilation may be needed.

Treatment of alkalosis

Metabolic alkalosis may be treated by giving fluids and electrolytes while treating the cause of fluid loss. Respiratory alkalosis is treated by ensuring the patient has sufficient oxygen and treating the underlying cause of hyperventilating, such as an infection, pain, or anxiety.


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