Total bilirubin measurement by photometry on a blood gas analyzer: potential for use in neonatal testing at the point of care.

The results are summarized in Table 1. The baseline absorbance of untreated plasma samples was significantly higher (0.106 6 0.076) than that of plasma samples treated with PEG (0.007 6 0.003; t 5 5.95; P ,0.001). There were no significant differences between the recovered ICG concentrations and the expected values at any of the four dye concentrations. Zweens and Frankena (4 ) demonstrated that the optimal concentration of PEG to eliminate baseline turbidity in plasma samples containing Evan’s blue dye was 240 g/L. In the present investigation involving ICG, we found that a PEG concentration of 240 g/L produced a 20% loss of the dye in the pellet. This finding is consistent with reports by Baker (1 ) and Kawasaki et al. (5 ), who demonstrated that a portion of ICG binds to non-albumin plasma proteins. A better PEG concentration for studies involving ICG was 120 g/L. This concentration produced the same beneficial reduction in the variable background absorbance as the higher concentrations but did not produce appreciable dye losses, and the recovery of ICG was nearly 100% across a range of typical ICG concentrations that are likely to be encountered in a patient study. Treatment of plasma samples with PEG may eliminate the need to perform separate calibration curves for each test subject. The standard protocol has been for participants to donate an initial blood sample that is used to develop an individual calibration curve. Individual curves have been necessary because the turbidity in the baseline plasma inflated the absorbance readings of subsequent samples. We have demonstrated that treating plasma samples with PEG effectively reduces the turbidity of plasma. Use of a common calibration curve to analyze plasma samples from more than one person is an appealing prospect because it can save time and reduce the volume of blood required to perform a study.