We all know how important oxygen is to our bodies. Breathing properly and having the right amount of oxygen in the blood is essential to staying healthy. So, sometimes doctors need to know exactly how much oxygen and carbon dioxide are in your blood. That's when this test called ABG (Arterial Blood Gas) is done.
What is this ABG (Arterial Blood Gas) test?
Simply put, an ABG (Arterial Blood Gas) test is a test that uses a blood sample taken from your artery to measure the amount of oxygen and carbon dioxide in your blood. Think about it, there are two types of blood vessels in our body, one is the arteries, and the other is the veins. The arteries carry clean, oxygen-rich blood from the heart to the rest of the body. So, for this ABG test, a blood sample is taken from those arteries.
This test not only measures oxygen and carbon dioxide, but also the acid-base balance , or pH, of your blood. Our bodies normally regulate the levels of oxygen and carbon dioxide in our blood very closely. If the oxygen level in our blood drops (which we medically call `hypoxemia`), it can cause very serious problems . It can damage your brain and heart in particular.
The ABG test helps doctors understand diseases related to your respiratory system , circulatory system , and metabolic processes (the way you convert the food you eat into energy). This is especially important in emergency situations .
There is another test called "blood gas analysis." In this test, a blood sample can be taken from anywhere in the body (an artery, a vein, or a capillary). However, in the ABG test, blood must be taken from an artery .
This ABG test has several other names:
- Blood gas test
- Arterial blood gases
- ABG
- Blood gas analysis
What exactly does an ABG test measure?
An ABG test typically measures:
- Oxygen content (O2CT) : This measures how much oxygen is in your blood.
- Hemoglobin : Hemoglobin is a protein found in our red blood cells that carries oxygen throughout the body. This measures the amount of hemoglobin.
- Oxygen saturation (O2Sat) : This measures how much oxygen is being carried by the hemoglobin in your blood.
- Partial pressure of oxygen (PaO2) : This measures the pressure of oxygen dissolved in your blood. It shows how well oxygen is getting into your blood from your lungs.
- Partial pressure of carbon dioxide (PaCO2) : This measures the amount of carbon dioxide in your blood and how well carbon dioxide is being removed from your body.
- pH (`pH`) : This measures the balance between acids and bases in your blood. Normally, the pH of blood should be between 7.35 and 7.45. Anything lower than that is considered too acidic, and anything higher than that is considered too basic or alkaline .
- Bicarbonate (`Bicarbonate - HCO3`) : This is calculated using pH and PaCO2. It determines the amount of a base compound formed from carbon dioxide.
When is an ABG test done?
Doctors usually order an ABG test in cases like these:
- Emergency medicine : This refers to illnesses or accidents that require immediate medical attention.
- Anesthesiology : The field of medicine concerned with the care of patients before, during, and after surgery.
- Pulmonology : The field that deals with diseases related to your respiratory system.
Doctors use an ABG test to diagnose several conditions, including:
- Acute respiratory distress syndrome (ARDS) : This is a life-threatening lung condition that causes a dangerously low level of oxygen in the blood. It can be caused by conditions such as sepsis and COVID-19.
- Severe sepsis : Sepsis is a life-threatening medical emergency caused by your body's response to an infection.
- Septic shock : This is also a life-threatening condition in which your blood pressure drops dangerously after an infection.
- Hypovolemic shock : An emergency condition in which the heart is unable to pump enough blood to the body due to excessive blood loss or loss of other fluids.
- Diabetes-related ketoacidosis (DKA) : This is a serious, life-threatening complication that affects people with diabetes (especially type 1 diabetes) and undiagnosed type 1 diabetes. It causes the blood to become acidic.
- Renal tubular acidosis (RTA) : In this condition, your kidneys don't properly remove acids from your blood into your urine, causing your blood to become more acidic.
- Acute respiratory failure : This is when fluid builds up in the air sacs in your lungs, making it difficult for the lungs to release oxygen into the blood.
- Acute heart failure : This is a condition in which the heart suddenly becomes weak and its function is limited.
- Cardiac arrest : This is when your heart suddenly stops beating.
- Asthma attack : A sudden increase in asthma symptoms caused by tightening of the muscles around the airways.
- Inborn errors of metabolism : These are rare, genetic (inherited) conditions in which your body cannot properly convert food into energy.
If you have any of these lung conditions, your doctor may also do an ABG test to see if your treatment is working properly:
- Asthma
- Chronic obstructive pulmonary disease (COPD)
- Cystic fibrosis
- Heart disease
Who performs the ABG test?
A respiratory therapist usually takes blood for an ABG test. They take blood from an artery in your wrist, arm, or groin. They then test the blood sample themselves, or they send it very quickly to a laboratory, where medical laboratory scientists test the sample.
What happens before an ABG test?
Before the respiratory therapist takes blood from your wrist, they may perform a blood flow test called the Allen test . This involves holding your arm up with your hand in a fist. The therapist will press on the artery in your wrist for a few seconds. This simple test checks whether both arteries in your wrist are working properly and are open.
If you are on supplemental oxygen therapy, your therapist may turn off your oxygen about 20 minutes before the blood draw. This is called a room air test . However, if you cannot breathe without supplemental oxygen, they will not do this test.
What kind of experience do you get when you have an ABG test?
Most blood tests take blood from your vein. But for an ABG test, the respiratory therapist takes a blood sample from your artery . This is because arterial blood has a higher oxygen content than venous blood.
The respiratory therapist usually takes blood from the radial artery on the inside of your wrist. Sometimes they may also take blood from an artery in your arm (brachial artery) or groin (femoral artery).
If a newborn baby needs an ABG test, a doctor may take blood from the baby's heel or umbilical cord.
Important: Taking blood from an artery can usually be a little more painful than taking blood from a vein. This is because arteries are further into the body than veins, and they have nerves around them. You may feel a little dizzy, lightheaded, or nauseous when your blood is taken.
These are the steps to follow when taking blood for an ABG test:
1. You will be seated in a chair or lying on a bed. The respiratory therapist will find an artery, usually on the inside of your wrist. They may also use an ultrasound scan (`ultrasound imaging`) to find the artery.
2. Once the artery is found, the area is cleaned and disinfected.
3. Then they will insert a small needle into your artery and take a blood sample. You may feel a sharp pain as the needle goes into the artery.
4. After inserting the needle, a small amount of blood is collected into a syringe.
5. After they have taken enough blood for the test, they will remove the needle and apply pressure to the area with a piece of cotton or gauze to stop the bleeding. If you are taking blood-thinning medication, you may need to hold the pressure for five to ten minutes or longer.
6. They put a bandage on the area. Then the job is done.
What can you expect after an ABG test?
You may feel some bruising and/or soreness where the needle was inserted. Your doctor may tell you not to lift anything heavy for 24 hours after the blood draw.
Are there any risks with the ABG test?
If the respiratory therapist performs this test correctly, the ABG test is very low risk . Everyone's arteries are different sizes, and they vary from one side of the body to the other. So it can be a little more difficult to draw blood from some people than others.
The risks associated with having blood drawn for an ABG test are very low, but things like this can happen:
- Feeling dizzy or lightheaded.
- Having to poke the needle several times to find the artery.
- A blood clot (a hematoma - a collection of blood under the skin).
- Excessive bleeding.
- Infection (there is a small risk anytime the skin is broken).
How long does it take to get the results of the ABG test?
ABG tests usually provide results very quickly . Respiratory therapists and laboratory scientists usually use automated blood gas analyzers, which can provide results within 10-15 minutes.
What do the results of the ABG test say?
Blood test reports, including ABG test reports, typically contain the following information:
- The name of the blood test or what was measured in your blood.
- The number or measurement of your blood test result.
- That is the normal measurement range for the test.
- Information that shows whether your result is normal, abnormal, or high or low.
If your ABG test results are abnormal, it could mean things like:
- You're not getting enough oxygen.
- You're not exhaling enough carbon dioxide.
- Your blood has a pH imbalance (either too acidic or too alkaline).
An ABG test can help diagnose certain diseases. If your results are abnormal, your doctor may order further tests (such as other blood tests and/or scans) to confirm or rule out a diagnosis.
What are the normal values for an ABG test?
Normal ranges can vary slightly from lab to lab. When you get your blood test results, they will include information that shows what the normal ranges are for each measurement from that lab. If you have any questions about your results, be sure to ask your doctor .
Generally, the average values at sea level are as follows:
- pH : 7.35-7.45
- Partial pressure of oxygen (`PaO2`) : 75 to 100 millimeters of mercury (mmHg)
- Partial pressure of carbon dioxide (`PaCO2`) : 35 to 45 mmHg
- Bicarbonate (`HCO3`) : 22 to 26 milliequivalents per liter (mEq/L)
- Oxygen Saturation (`O2Sat` or `SaO2`) : 95% to 100%
At altitudes of 3,000 feet (900 meters) and above, average oxygen levels are much lower.
When should I see my doctor?
If you have a chronic lung disease like COPD or asthma, you will likely need to see your doctor regularly and have ABG tests to make sure your treatment is working properly. If you develop any worrying symptoms related to your lung disease, talk to your doctor as soon as possible.
Finally, things to remember
An ABG test is a useful diagnostic tool , especially in some emergency situations. Doctors also use this test to monitor certain health conditions. If you are having an ABG test, keep in mind that it is a slightly different procedure than a regular blood test, and it can be a little more painful. If you have any questions about the procedure or what to expect, don't hesitate to ask your doctor . They are here to help you.
` Blood gas test, arterial blood gas, oxygen, carbon dioxide, pH value, respiratory system, medical tests
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