The Science Journal of the American Association for Respiratory Care

1996 OPEN FORUM Abstracts

EVALUATION OF THE FETAL HEMOGLOBIN CHANNEL ON THE IL 682 CO-OXIMETER

Andres M Pierce PhD, Charles Morash RRT, Bruce Randall MS RRT, Lynn Maillet MS, Instrumentation Laboratory, Lexington MA and Boston Regional Medical Center, Stoneham MA

BACKGROUND: IL has developed a new CO-Oximeter instrument for the multicomponent analysis of hemoglobin derivatives. The IL682 CO-Oximeter uses the same principle as its predecessors for determining the percentages of O_{2}Hb, CO Hb, Met or Fe^{3+} Hb, and HHb (Deoxy Hb) in a whole blood sample. The IL 682 CO- Oximeter uses the differences in the molar absorptivities of hemoglobin in the visible wavelength region to determine these Hb species. Subtle differences in the absorbance spectra of fetal hemoglobin (Hb F) result in some inaccuracy when analyzing fully oxygenated neonatal or cord blood samples with high Hb F concentrations. Typically a false elevation in the % COHb and a concomitant decrease in the %O_{2}Hb occurs when these samples are measured in the adult mode. Methods: IL has generated an algorithm for calculating the % HbF in whole cord blood samples which was correlated to the alkali denaturation reference method (r^{2}= 0.9678, n=5). Using this data, a unique set of HbF coefficients was generated based on the absorbance spectra of fetal hemoglobin and incorporated into a new fetal hemoglobin channel on the IL 682 CO-Oximeter. In this study, we analyzed 31 cord blood samples run in the fetal hemoglobin mode on the IL 682 CO-Oximeter and on the Radiometer OSM3 Hemoximeter. Routine quality control of the IL 682 was performed using IL's Multi 4 (r) CO-Oximeter control (CV %'s of 0.97%, 0.28%, and 0.74% for THb, % O_{2}Hb, and % COHb). Results: Analysis using the two tailed t-test for paired data gave no statistical difference of the means (calculated value of 0.003894, n-1=27 vs. 2.052 critical value, 95% C.I.) and acceptable correlation (r= 0.881, n=28) for the estimation of % Hb F. Similarly, no statistical differences were observed for the means of % COHb, % O_{2}Hb, and % Met Hb when using the two-tailed paired t-test (t=0.8384, 0.3129, and 0.0000, respectively, n-1=27 vs. 2.052 critical value, 95% C.I.). Bias plot analysis revealed a trend where the mean value of % Met Hb for the IL 682 CO-Oximeter was slightly higher than that of the OSM3 (mean value of the IL 682=0.31 vs. mean of the OSM3 =-0.02, and did give a statistical difference between the standard deviations (F=1.84 calculated vs. F=1.83 critical value). Additionally we tested the Hb F extinction matrix in the presence of elevated bilirubin concentrations, since bilirubin is a common interferent in neonatal specimens. Samples with concentrations of bilirubin equal to 100 mg/L or less, showed on statistical difference from baseline samples (0 mg/L bilirubin concentration). At concentrations of 300 mg/L, bilirubin's presence did not affect the % MetHb and % HHb but had a slight effect on the other species where the measured % O_{2}Hb was decreased by an average of 1.4% (mean values 99.72% at 0 mg/L bilirubin vs. 98.30 +/- 0.35% at 300 mg/L), and the % COHb was increased by 2.5% from baseline samples (means -2.81% at 0 mg/L vs.-0.36 +/-0.34% at 300mg/L). Conclusions: This study then confirms that the IL 682 CO-Oximeter can accurately determine the percentage Hb species in neonatal or cord blood specimens when analyzed in the fetal Hb mode and is not affected by bilirubin in samples at concentrations up to 100 mg/L.

Reference: OF-96-004

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