As the blood travels through the body, it delivers oxygen to the tissues and organs before traveling back through the heart and into the lungs to reoxygenate.

A blood oxygen level that is too low can indicate a variety of problems. Some of these conditions are minor, but others are far more serious.

Oxygen in the Blood

Red blood cells contain a protein called hemoglobin, which gives them their red color. Oxygen binds to hemoglobin, and the red blood cells carry it around the body. When they reach their destination, they release the oxygen.

Red blood cells are shaped like thin discs that can change shape and squeeze into small and narrow blood vessels, ensuring that oxygen gets everywhere it needs to go.


Normal Blood Oxygen Level

What is considered a normal blood oxygen level depends on how it is measured. If measured directly from blood taken from an artery, a normal blood oxygen level is between 75 and 100 mm Hg.

If the oxygen level is read through the skin using a pulse oximeter, a normal reading is between 95 and 100 percent.


Abnormal Blood Oxygen Levels

A below-normal blood oxygen level is called hypoxia. Checking the blood oxygen through the skin can indicate hypoxia, especially if the level is less than 90 percent, but the condition is typically confirmed with a blood test as they are more accurate.

Many things can cause low blood oxygen. Some of the causes are situational, while others indicate a problem.


Factors that Affect Blood Oxygen

Some less serious causes of low blood oxygen include sleep apnea, strong pain medications, and being at a high altitude where less oxygen is available.

When using a pulse ox monitor to determine blood oxygen, a number of factors can affect accuracy, including artificial nails, nail polish, skin temperature, and skin color.


Cardiac Causes of Low Blood Oxygen

More serious causes of low blood oxygen include heart conditions such as heart defects. Anything that interferes with the blood circulating into the lungs can cause low blood oxygen, as it prevents the blood from getting reoxygenated.

Anemia can also cause low blood oxygen because having fewer red blood cells mean that the blood cannot carry adequate amounts of oxygen.


Pulmonary Causes of Low Blood Oxygen

Many lung conditions can cause low blood oxygen. These include asthma, bronchitis, emphysema, COPD, pulmonary edema, blood clots, and scarred or damaged lungs.

When low blood oxygen results from lung conditions, it is because the lungs cannot properly reoxygenate the blood as it circulates through. These conditions vary in severity. Some can require emergency medical attention, while others are chronic and need long-term management.


Pulse Oxymetry

Pulse oxymetry is an easy way to monitor blood oxygen at home. These small devices clip onto the finger or toe or attach to the earlobe. The device passes beams of light through the skin and reads the amount of oxygen in the blood.

This method of measuring blood oxygen is indirect, and it is not as accurate as a direct measurement.


Arterial Blood Gas

An arterial blood gas is the most accurate way to measure blood oxygen. Blood samples drawn directly from an artery are analyzed, and test results show not only the blood oxygen but also the carbon dioxide, pH, and bicarbonate in the blood. Doctors can tell a lot about the patient's condition by looking at the results of arterial blood gas.



Hypoxia treatment depends on the blood oxygen level and the underlying health issues. In some cases, the person uses an inhaler to deliver medicine directly to the lungs.

People who have an underlying chronic condition and experience hypoxia may require oxygen therapy. Depending on the severity of the hypoxia and the person's health, they may require oxygen at all times or during activity.



To prevent hypoxia, maintaining heart and lung health is important. To increase oxygen levels in the blood, there are some simple things you can do, including deep breathing exercises, drinking plenty of water, eating a healthy diet, and quitting smoking.

Regular exercise is also essential, and even things like yoga or walking can help.


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