What Is Blood Oxygenation?

The amount of oxygen being carried by the blood to the body's organs and tissue is called the blood oxygenation, or oxygen saturation level. This dissolved oxygen is measured through a few methods to ensure that an adequate supply is naturally furnished by the lungs. The blood oxygenation level is calculated by analyzing a blood sample in the laboratory, in an arterial blood gas test, or by attaching a light sensor clip to the fingertip.

The blood's hemoglobin molecules can be medically analyzed in a few different ways to verify that enough oxygen is on board to keep the body functioning properly. The two methods measure the level of oxygen (O2), on average, that occupies the hemoglobin molecules. As many as four oxygen (O2) molecules can be held by each hemoglobin molecule, so 100 could contain a maximum of 400 oxygen molecules. This is the maximum score — 100 percent.

If a patient has an average of two or three oxygen molecules occupying most hemoglobin molecules, the blood oxygenation score will be closer to 50 percent or 75 percent, respectively. The blood test is considered the more accurate means of determining an exact percentage. Any score above 95 percent is considered strong, though certain factors like age and weight will play a role.

The fingerclip technique, called a pulse oximeter, works by shining light through the skin and gauging the color of the blood, which changes slightly according to how much oxygen is present. The clip also may be attached to a toenail, earlobe or even over the nose, depending on the type of equipment used. This test can be performed at home, if the patient has invested in the device. A blood test is usually performed when the physician strongly suspects that a blood oxygenation problem exists. This test is considered the most accurate appraisal of blood oxygen levels.

Before a blood sample test is performed, a physician is likely to perform a cursory test to make sure the blood is being drawn from an area where arterial blood flow is representative of the entire body. Both sides of the arm are pinched, just above where the blood will be drawn, which turns the area below the pinch pale. When the doctor releases the pinch, it is rudimentary to analyze how quickly the color returns to the skin.

A pulse oximeter can calculate results immediately. Likewise, it only takes about 15 minutes for a lab technician to perform an arterial blood gas examination. If a patient's blood oxygenation level is determined to be low or borderline risky, a doctor may recommend supplemental oxygen, medication or more testing.