Accuracy of Pulse Oximeter
The most accurate way to determine the "true" oxygen saturation level is to take a blood sample and run tests against the sample. Even so, repeated tests on the same sample may yield slightly different results . Unlike using a ruler to obtain the distance between two points, there are too many factors involved. The cost associated with this test is high and can only be performed in a medical lab.
Pulse oximeter provides an indirect method. The derived blood SpO2 level is calculated from on a formula based on the light absorption by venous vessels. 1% to 2% variation from the "true" value is normal with this technology. The accuracy of a pulse oximeter is stated in terms of the root-mean-square (rms) difference between measured SpO2 values and co-oximetry (SaO2) reference values. With a accuracy rating of ±2%, a well-behaved oximeter may sometimes have some readings that are off by as much as 6%. Pulse oximeter is a sensitive device and many factors, such as random noise, motion, and physiological conditions, can cause the erroneous readings . The accuracy published in the specifications of a pulse oximeter is based on the performance of a collection of test samples rather than each individual reading.
In general, with an accuracy rating of ±2%, saturation readings in the 90-100% range would have an accuracy of less than 2%; saturation readings in the 80-90% range would have an accuracy of about 2%; saturation readings in the 70-80% range would have an accuracy of greater than 2%. The accuracy would also decrease with low blood perfusion and low heart rate.
- Paul Batchelder and Dena Raley, "Maximizing the Laboratory Setting for Testing Devices and Understanding Statistical Output in Pulse Oximeter", International Anesthesia Research Society, Vol. 105, No. 8, August 2007.