BiliChek Service Manual
7
1014988
The light reflected from the skin of neonates and collected by
the BiliChek Non-Invasive Bilirubin Analyzer is analyzed with
a highly sophisticated, proprietary algorithm to generate a serum
bilirubin measurement. The major skin components which
impact the spectral reflectance in newborns are (1) dermal
maturity, (2) melanin, (3) hemoglobin, and (4) bilirubin. The
intensity of the reflected light is converted to absorbance units,
Optical Density (OD), for analysis. The total OD at each
measured wavelength is equal to the sum of the component ODs.
This is represented mathematically as: OD
TOTAL
= OD
DERM
+
OD
MEL
+OD
HEME
+OD
BILI
By utilizing known spectral
characteristics of each component, the contribution to the total
OD can be sequentially subtracted until bilirubin is all that is
remaining.
Theory of Operation (continued)
Non-Invasive Skin Spectral Components
1
1
Jacques, S., Saidi, I., Ladner, A., and D. Oelberg. Developing and optical
fiber reflectance spectrometer to monitor bilirubinemia in meonates.
Each of these components have also been considered in the
development of the algorithm by which the BiliChek Non-
Invasive Bilirubin Analyzer computes the bilirubin measurement.
By measuring the intensity of the reflected light at more than
100 individual wavelength bands across the visible spectrum, a
spectral analysis can be performed. By normalizing against a
reference standard, the BiliCal
®
Individual Calibration tip, the
variations over time of the bulb and the photo-detectors are
eliminated. The peak absorption of the bilirubin is at
approximately 460nm as measured by subtracting the absorption
of the other components from the total skin absorption. This is
represented by the equation below.
OD
BILI
= OD
TOTAL
-OD
MEL
-OD
HEME
-OD
DERM
The absorption of light by a molecule is proportional to its
concentration. Therefore, the absorption of bilirubin, as
calculated above, is proportional to the concentration of bilirubin
in the subcutaneous capillary beds and subcutaneous tissue. By
subtracting the contribution of the aforementioned components,
the bilirubin absorbance can be quantified and is correlated to
the laboratory total serum bilirubin levels.
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