Unexpectedly low pulse oximetry measurements associated with variant hemoglobins: A systematic review

Pulse oximetry estimates arterial blood oxygen saturation based on light absorbance of oxy‐ and deoxy‐hemoglobin at 660 and 940 nm wavelengths. Patients with unexpectedly low SpO 2 often undergo cardio‐pulmonary testing to ascertain the cause of their hypoxemia. However, in a subset of patients, a variant hemoglobin is responsible for low SpO 2 measurements. The extent of this problem is unclear. We performed a systematic literature review for reports of low SpO 2 associated with variant hemoglobins. We also reviewed unpublished cases from an academic hemoglobin diagnostic reference laboratory. Twenty‐five publications and four unpublished cases were identified, representing 45 patients with low SpO 2 and confirmed variant hemoglobin. Fifty‐seven family members of patients had confirmed or suspected variant hemoglobin. Three low oxygen affinity variant hemoglobins had concordantly low SpO 2 and SaO 2 . Eleven variant hemoglobins were associated with unexpectedly low SpO 2 measurements but normal SaO 2 . Hemoglobin light absorbance testing was reported in three cases, all of which showed abnormal absorption spectra between 600 and 900 nm. Seven other variant hemoglobins had decreased SpO 2 , with unreported or uncertain SaO 2 . Twenty‐one variant hemoglobins were found to be associated with low SpO 2 . Most variant hemoglobins were associated with spuriously low SpO 2 . Abnormal absorption spectra explain the discrepancy between SpO 2 and SaO 2 for some variants. The differential diagnosis of possible variant hemoglobin ought to be considered in asymptomatic patients found to have unexpectedly low SpO 2 . The correct diagnosis will help to spare patients from unnecessary investigations and anxiety. Am. J. Hematol., 2010. © 2010 Wiley‐Liss, Inc.