CASE REPORT hemoglobin-H; pulse oximetry Evaluation of Pulse 0ximetry Hemoglobin-H Disease in Anemia From From the Department of Emergency Medicine, University of Massachusetts, Worcester. Received for publication July 1, 1991. Revision received October 11, 1991. Acceptedfor publication December 9, 1991. Gregory D Jay, MD, PhD Francis P Renzi, MD, FACEP A patient with hemoglobin-H (Hb-H) disease developed an acute hemo- lytic crisis after treatment with trimethoprim and sulfamethoxazole. Despite her poor clinical condition and profound anemia (Hb, 2.7 g/dL), pulse oximetry continued to demonstrate a high 02 saturation percent- age, Manipulation of Beer's law shows that anemia theoretically should not affect pulse oximetry values. The literature describes the effects of dyshemoglobinopathies such as carboxyhemoglobinemia and methe- moglobinemia on 02 saturation percentage measured by pulse oxime- try, but the effect of genetic hemoglobinopathies on pulse oximetry values is largely unreported. Because most hemoglohinopathies do not significantly change the protein-heine electronic interaction, the values of 02 saturation percentage determined through pulse oximetry should remain clinically valid. Hb-H is an exception to this generalization; as in patients with carboxyhemoglobinemia, pulse oximetry measurements showing high 02 saturation percentage do not correspond to high levels of oxygen available for delivery to tissues. [Jay GD, Renzi FP: Evaluation of pulse oximetry in anemia from hemoglobin-H disease: Ann Emerg Med May 1992;21:572-574.] INTRODUCTION The widespread use of pulse oximetry in the emergency department has significantly changed the course of rapid patient evaluation. Emergency physicians should be aware of the limitations of this technology as well as causes of mea- surement error. Fingernail polish, 1 ambient light, 2 sensor location, 3 methemoglobinemia,4, 5 vasoconstriction,6 and anemia 7 have all been associated with erroneous readings of 0 2 saturation percentage (Sa02). In carboxyhemoglobine- mia, the pulse oximeter overestimates Sa02.8 Some of these confounding chnical variables and other hematologic pathologies lack adequate quantitative study. The literature contains only a few references2, 9 to the accuracy of pulse oximetry in anemic patients and only one report 10 examining this test in dogs with life-threatening anemia. Clinicians might anticipate that pulse oximetry in the latter situation would either underestimate SaO z or would not work below some "critical" hematocritJ 1 This case report explores this notion and identifies hemoglobin-H (Hb-H) as an abnormal hemoglobin with enhanced oxygen affinity that may affect • 130/572 ANNALS OF EMERGENCYMEDIClNE 2 1 : 5 MAY1992