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To the Editor:
The careful study of Foster et al. (1) reminds us of the difficulty of assessing amniotic fluid bilirubin absorbance in specimens contaminated by blood. However, it is not correct, as Foster et al. conclude, that bilirubin absorbance cannot be appropriately assessed in specimens contaminated in this manner.
To eliminate interference from nonbilirubin pigments, my colleagues and I (2) exploited the fact that bilirubin is highly photolabile whereas interfering chromagens such as hemoglobin and methemoglobin are remarkably photostable. A few minutes of exposure to an intense light source (such as that from an ordinary slide projector) eliminates most of the bilirubin absorbance and allows the absorbance present before irradiation to be determined as described in the next paragraph. Slide projectors of a type similar to the one used here continue to be manufactured, e.g., the Kodak Carousel 4600 (Eastman Kodak Company) or the Vivitar 5000 AF (Vivitar USA). These and similar projectors and their replacement lamps can be purchased at local camera stores or via the internet at sources such as Amazon.com. They are also readily obtainable "used" at Ebay.com. Furthermore, the light sources in modern high-intensity projectors commonly used to display...