The key difference between SAO2 và SPO2 is in the type of measurement of O2 levels in the blood. SAO2 or Saturation of Oxygen is the direct measurement of O2 bound to lớn heme protein of hemoglobin in the blood. SPO2 measurement or oximetric measurement of O2 bound to hemoglobin is an indirect measurement of saturation of haemoglobin with O2.

SAO2 & SPO2 are measured during different disease conditions khổng lồ monitor the màn chơi of available O2­ in hemoglobin. The saturation levels of O2 bound to lớn hemoglobin will provide details regarding the efficiency of the alveolar lung system.

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1. Overview & Key Difference2. What is SAO23. What is SPO24. Similarities Between SAO2 và SPO25. Side by Side Comparison – SAO2 vs SPO2 in Tabular Form6. Summary

What is SAO2?

Saturation of O2 (SAO2) in blood defines the percentage of hemoglobin binding sites that occupied with O2. Each hemoglobin molecule can occupy four O2 molecules as it can allosterically modify its conformation to lớn facilitate binding of O2 khổng lồ its binding site. The normal SAO2 value of a healthy individual occurs between 95 – 100 %. However, this may increase during conditions such as polycythemia và hyper ventilation. SAO2 decreases during anemia, hypoventilation, and bronchospasm.

Figure 01: Co-Oximeter

The co-oximeter measures SAO2. The ratio between oxyhemoglobin lớn all other types of hemoglobin provides the SAO2 value. Other types of hemoglobin include deoxyhemoglobin, methaemoglobin, carboxyhemoglobin, sulfhemoglobin & carboxy sulfhemoglobin.

What is SPO2?

SPO2 or the oxygen saturation measurement by pulse oximetry measures the functional saturation of hemoglobin. SPO2 is the ratio between the amount of oxygenated hemoglobin to the sum of deoxyhemoglobin and oxyhemoglobin. Thus, the SPO2 value will not be the same as the SAO2 value.

This method of obtaining the saturation of O2 in hemoglobin is more efficient and rapid in comparison with the co-oximeter measurement.

Figure 02: SPO2

The SPO2 levels in a healthy individual should be more than 94%. The levels can increase or decrease for different health conditions as in SAO2.

What are the Similarities Between SAO2 & SPO2?

Both SAO2 và SPO2 depend on the concentration of O­2 in blood.SAO2 & SPO2 measure the saturation of O2 in haemoglobin.Both the levels of SAO2 và SPO2 increase during hyper ventilation.The SAO2 và SPO2 levels decrease during hypo ventilation và anaemic.

What is the Difference Between SAO2 and SPO2?

SAO2 vs SPO2

SAO2 is the direct measurement of O2 bound to lớn heme protein of haemoglobin in the blood.SPO2 measurement is the oximetric pulse measurement of functional saturation of haemoglobin with O2.
 Saturation cấp độ in a Healthy Individual
SAO2 in healthy person should be 95 – 100%.SPO2 in healthy person should be more than 94%.
Device Used for Measurement
Co-oximeter is used lớn measure SAO2.Pulse Oximeter is used to lớn measure SPO2.
 Invasiveness of the Technique Used
Invasive technique is used to lớn measure SAO2. It uses the measurement of O2 saturation in arterial blood.No-invasive technique is used lớn measure SPO2. It uses earlobes or fingertips for measurement.
SAO2 measurement is slower than SPO2SPO2 measurement is raid than SAO2
Less efficient.More efficient.

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Summary – SAO2 vs SPO2

Measurement of O2 saturation levels is very important during disease conditions to assess the respiratory levels and to check for cardiac and respiratory health. Increase or decrease of these saturation levels indicates the disease conditions. SAO2 and SPO2 differ in the method they use for measuring O2 saturation in blood. That is, SAO2 ­­measures the total O2 bound lớn haemoglobin using co-oximeter whereas SPO­2 measures the O2 bound to haemoglobin by pulse oximeter method. Further, SAO2 is a direct measurement of saturation of O2 in the blood while SPO2 is an indirect measurement of SAO2. This is the difference between SAO2 và SPO2.


1.“Meaning of Blood Oxygen Saturation SpO2.” Meaning of Blood Oxygen Saturation SpO2 – HeathcareFor Home. Available here 2.Haws, Sandra. “Oxygen Saturation (SaO2).” NRSNG, 7 Sept. 2016. Available here

Image Courtesy:

1.’Co monitor’By James Heilman, MD – Own work, (CC BY-SA 3.0) via Commons Wikimedia2.’OxyWatch C20 Pulse Oximeter’By Thinkpaul – Own work, (CC BY-SA 3.0) via Commons Wikimedia

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