Noninvasive hemoglobin measurement in pregnancy

Abstract

Hemoglobin measurement is one of the most frequently requested laboratory tests in amaternity setting. Traditional laboratory estimation assesses hemoglobin at a given time point. However, recent advances enable the continuous and noninvasive measurement of total hemoglobin [1,2]. The ability to assess hemoglobin continuously is of particular value in an emergency setting, in the early detection of hemorrhage, and in the identification of cases that warrant intervention, fluid replacement, and blood transfusion. Rapid access to measurements via devices such as the SpHb Pulse CO-Oximeter (Masimo, Irvine, CA, USA) in a clinical outpatient setting also facilitates the identification of the need for additional blood investigations and the instigation of supplemental iron therapy earlier in pregnancy. The aim of the present study was to validate continuous and noninvasive hemoglobin assessment in an outpatient obstetric setting using the SpHb Pulse CO-Oximeter and to compare the valueswith traditional laboratory measurements of hemoglobin. Between August 2 and 31, 2010, 125 women were recruited from the prenatal clinic of the National Maternity Hospital, Dublin, Ireland, at the time of phlebotomy for standard prenatal laboratory hemoglobin estimation. The SpHb Pulse CO-Oximeter was calibrated and 3 noninvasive estimations of hemoglobin were taken and recorded, with consent. Approval was obtained from the institutional ethics committee. The comparison ofmeans between laboratory hemoglobin and SpHb estimation was carried out via t test and f test, as appropriate. A Bland– Altman plot was used to determine the accuracy and precision of the noninvasive test as an alternative to invasive testing in an outpatient clinical setting (Fig. 1). The mean difference between the 2 methods was 0.47 g/dL. The upper limit of agreement was 3.46 and the lower limit was −2.50. Seven (5.6%) of the 125 samples were outside these limits but only 1 result was outside the 95th confidence interval of the limits. The limits of agreement were sufficient to be confident that noninvasive hemoglobin assessment is accurate in the prenatal setting. The present study showed that noninvasive hemoglobin measurement from Pulse COOximetry provides clinically acceptable accuracy comparable to that of traditional hemoglobin testing. Anemia in pregnancy has implications for maternal, fetal, and neonatal wellbeing. The goal of early identification of anemic patients is to facilitate earlier intervention and prevention of serious sequelae. Prenatally, the SpHb Pulse CO-Oximeter could facilitate the earlier identification andmanagement of anemic patients because, traditionally, women in Ireland who are identified as being anemic are contacted by post following receipt of the blood report—a process that involves a variable time delay between identification and treatment. Further advantages of noninvasive continuous hemoglobin measurement in an obstetric setting include the potential for a more efficient patient triage system and, in a cost-conscious era, the possibility of limiting costly “out-of-hours” laboratory investigations. The identification of a subset of patients in any hospital population who require increased monitoring and early transfusion to avoid decompensation is the ideal.