Pulse oximetry is accurate in acute anemia from hemorrhage

Ann Emerg Med. 1994 Jul;24(1):32-5. doi: 10.1016/s0196-0644(94)70158-x.


Hypothesis: Pulse oximetry is an accurate, noninvasive assay of oxygen saturation percentage (SaO2) in acutely severe anemia (less than 5 g/dL).

Design: A paired comparison of SaO2 by pulse oximetry (SpO2) and arterial blood gas analysis (SaO2) in patients with either acute gastrointestinal bleeding or blunt trauma with hematocrit of less than 20%.

Setting: An academic emergency department in a tertiary referral hospital with a Level I trauma center.

Participants: Seventeen nonhypoxic patients were identified with initial hematocrit of less than 20% over a 9-month period.

Measurements and main results: Determination of SaO2 by pulse oximetry and arterial blood analysis was not statistically significantly different (P < .05) over a range of hemoglobin levels from 2.3 to 8.7 g/dL. The observed mean difference between SpO2 and SaO2 was 0.53 +/- 0.23% (mean +/- SEM; n = 17). The 95% confidence interval associated with this difference score ranged from 0.044 to 1.014.

Conclusion: Despite reports that pulse oximetry is inaccurate below a hemoglobin concentration of 5 g/dL, our study suggested that this technology is accurate and reliable at 2.3 g/dL for nonhypoxic SaO2 values (SaO2 of more than 93%). The anemic endpoint where pulse oximetry either becomes inaccurate or simply fails to work has not been determined. Pulse oximetry overestimates SaO2 on average by 0.53% over a range of hemoglobin concentrations from 2.3 to 8.7 g/dL.

MeSH terms

  • Acute Disease
  • Adult
  • Aged
  • Aged, 80 and over
  • Anemia / blood*
  • Anemia / etiology
  • Female
  • Hematocrit
  • Hemoglobins / analysis
  • Hemorrhage / blood
  • Hemorrhage / complications*
  • Humans
  • Male
  • Middle Aged
  • Oximetry*
  • Oxygen / blood*


  • Hemoglobins
  • Oxygen