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• The need for explicit documentation of degree of skin pigmentation
  osacr,m jolobe
  Published on: 23 February 2023

• Published on: 23 February 2023

  The need for explicit documentation of degree of skin pigmentation

  • osacr,m jolobe, retired geriatrician British Medical Association

  In an observational study where 200 participants were black, 269 asian, and 4330 white, the authors demonstrated an inverse association between blood pressure and pulse oximetry accuracy that was not influenced by ethnicity[1]. In that study no specific mention was made of the degree of pigmentation in individual members of the ethnic subgroups, presumable because self-reported ethnicity was accepted as a surrogate for skin colour. This acceptance is in sharp contrast with the methodology in the study where subjects of African-American descent were further characterised by a description of their degree of pigmentation, using terminology such as "very darkly pigmented".. This was one of the earliest prospective studies conclusively to show that some oximeters overestimate arterial oxygen saturation in hypoxic subjects who are "darkly pigmented" [2].
  In retrospective studies such as the ones subsequently undertaken to explore the theme of racial bias in oximetry it was easy to fall into the trap of using ethnicity as a surrogate for skin colour[3],[4], largely because skin colour is not consistently recorded as part of the medical record[3]. Explicit description of skin colour also gets omitted when race and ethnicity are defined using self-reported demographic data[4].
  Future studies, however, might seek to ascertain whether or not skin pigmentation compounds the overestimation of oxygen saturation attributable to hypotension....

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  In an observational study where 200 participants were black, 269 asian, and 4330 white, the authors demonstrated an inverse association between blood pressure and pulse oximetry accuracy that was not influenced by ethnicity[1]. In that study no specific mention was made of the degree of pigmentation in individual members of the ethnic subgroups, presumable because self-reported ethnicity was accepted as a surrogate for skin colour. This acceptance is in sharp contrast with the methodology in the study where subjects of African-American descent were further characterised by a description of their degree of pigmentation, using terminology such as "very darkly pigmented".. This was one of the earliest prospective studies conclusively to show that some oximeters overestimate arterial oxygen saturation in hypoxic subjects who are "darkly pigmented" [2].
  In retrospective studies such as the ones subsequently undertaken to explore the theme of racial bias in oximetry it was easy to fall into the trap of using ethnicity as a surrogate for skin colour[3],[4], largely because skin colour is not consistently recorded as part of the medical record[3]. Explicit description of skin colour also gets omitted when race and ethnicity are defined using self-reported demographic data[4].
  Future studies, however, might seek to ascertain whether or not skin pigmentation compounds the overestimation of oxygen saturation attributable to hypotension. For those studies to be scientifically robust explicit documentation of the degree of pigmentation will have to be made., using, for example, strategies such as the Melasma Area and Severity Index[5], and the Willis and Earle scale[6], to mention a few.
  I have no funding and no conflict of interest
  References
  [1]Crooks CJ., West J., Morling J et al
  Inverse association between blood pressure and pulse oximetry accuracy: an observational study in patients with suspected or confirmed COVID-19 infection
  Emergency Medical Journal Article in Press
  doi:10.1136/emermed-2022-212443
  [2]Bickler PE., Feiner JR., Severinghaus SW
  Effects of skin pigmentation on pulse oximeter accuracy at low saturation
  Anesthesiology 2005;102:715-719
  [3]Valbuena VSM., Seelye S., Sjoding MW et al
  Racial bias and reproducibility in pulse oximetry among medical and surgical inpatients in general care in Veterans Administration 2013-19: multicenter retrospective cohort study
  BMJ 2022;378:e069775
  [4]Wong A-K I., Charpignon M., Kim H et al
  Analysis of discrepancies between pulse oximetry and arterisl oxygen saturation measurements by race and ethnicity and association with organ dysfunction and mortality
  JAMA Netweork OPEN 2021;4:e2131674
  [5]Pandya AG., Hynan LS., Bhore R et al
  Reliability assessment and validation of the Melasma Area and Severity Index(MASI) and a new modified MASI scoring method
  J Am Acad Dermatol 2011;64:78-83
  [6]Roberts W
  Skin type classification systems old and new
  Dermatology Clinics 2009;27:529-533

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  Conflict of Interest:
  None declared.

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