A LOW COST LED BASED BILIRUBIN METER
Description and Evaluation of a Low Cost Spectrophotometer Bilirubin Analyzer
L. A. L. Azeka and M. S. V. de Paiva
Department of Electrical Engineering, University of São Paulo
Avenida Trabalhador, São-carlense- 400, São Carlos, Brazil
Keywords: Jaundice, Bilirubin, Bilirubin meter, Spectrophotometry, Bilirubin Measurement.
Abstract: Jaundice is a disease caused by excessive levels of bilirubin in the blood. It is very common in newborns
and mainly in premature ones. By using resources such as LEDs with high luminous intensity and light to
digital photoreceptors, the present article describes and evaluates a low cost bilirubin meter (Bilimed),
which measures the total bilirubin in the blood serum samples of neonates, using the technique known as
direct spectrophotometry. Samples of newborns were collected and measured in the equipment. The result
was compared with reference values of a commercial bilirubinometer and with laboratory analysis in order
to evaluate the equipment’s performance.
1 INTRODUCTION
During the first weeks of a newborn’s life it is
common the appearance of the illness called
jaundice or hyperbilirubinemia defined as a
yellowish discoloration of the skin and the mucous
membranes, caused by the accumulation of a yellow
pigment called bilirubin (Odell, 1980). It is
manifested in about 60% of the newborns, being this
rate much bigger in premature neonates (Knudsen,
1989, Taksande et al., 2005). The increase of the
bilirubin concentration in the blood is generally
caused by the immaturity of the liver in processing
it, among other external factors such as breast-
feeding, hepatic malfunctions and blood
incompatibility (Askin and Diehl-Jones, 2003). The
high value of bilirubin is toxic for the brain and may
cause an encephalopathy called kernicterus, leaving
irreversible sequels to the child’s brain (Diamond,
1970).
The determination of the bilirubin levels is
generally carried out by three types of equipment
known as bilirubin meters or bilirubinometers: the
portable analyzer which measures the transcutaneous
bilirubin; the spectrophotometers which use the
photometric analysis in the blood serum to measure
the total bilirubin; and laboratory photometric
analyzers which analyze chemically reacted blood
samples by using scientific methods. The
transcutaneous bilirubinometers are the state-of-the-
art bilirubin measurement method and although
some authors have shown good correlation between
the transcutaneous bilirubin and the direct bilirubin
(Bhutani et al., 2000), not all the results show that
they are totally independent of factors such as race,
gestation and birth-weight (Maisels, 2006).
The bilirubinometers that use the
spectrophotometry as a principle - based on the light
absorption by the bilirubin molecule - are known as
direct spectrophotometers. This equipment was
firstly proposed in the 60s (Jackson, 1961) and
presented reliable results compared with the
transcutaneous method and other laboratory methods
(Grohmann et al., 2006).
The aim of this work is to describe the main
resources used by the direct spectrophotometer
Bilimed bilirubinometer, its technological
innovations, as well as to evaluate the equipment
performance through measurements in newborns
blood samples.
2 MATERIALS AND METHODS
The bilirubin molecule has a peak of light absorption
of about 455 nm. In this same wavelength there is
interference of the oxyhemoglobin molecule, being
necessary to measure its absorption (peaks of 545
nm or 575 nm) in order to make a compensation
(Roggan et al., 1999). The difference in absorption
231
Azeka L. and de Paiva M. (2009).
A LOW COST LED BASED BILIRUBIN METER - Description and Evaluation of a Low Cost Spectrophotometer Bilirubin Analyzer.
In Proceedings of the International Conference on Biomedical Electronics and Devices, pages 231-234
DOI: 10.5220/0001547702310234
Copyright
c
SciTePress
in the bilirubin and oxyhemoglobin 455 and 575 nm
wavelengths is used to measure the concentration
value of the total bilirubin. The figure 1 shows the
absorption spectrum of bilirubin and
oxyhemoglobin.
Figure 1: Absorption spectrum of bilirubin and
oxyhemoglobin. (Du et al., 1998, Zijlstra et al., 1991).
The direct bilirubinometer’s operation principle
is the use of a high intensity light source in order to
generate the necessary light for the
spectrophotometric process. A white Philips
Lumiled Luxeon K2 LED is used as light source and
a circuit drives the LED through signals sent by the
microcontroller. The capillary tube containing the
serum to be analyzed is inserted in the optic set
through a holder. The light goes through the sample;
the light shaft is split and goes through 455 and 575
nm band-pass filters. The luminous signal is then
transformed in digital signal by the TAOS TCS 230
photosensors which are positioned just after the
filters. This signal is sent to the microcontroller and
a routine converts the frequency sent by the
photosensor into a value correspondent to the
luminous intensity. In order to make the calculation
of the bilirubin absorption, a measurement of a
capillary tube containing distilled water, which will
serve as a reference value, is carried out. The signal
is processed and is converted into a concentration
value of total bilirubin (mg/l or μmol/dl).
The user interacts basically using two switches
and a LCD display. The figure 2 illustrates the
system.
Products which use high power LED have
recently revolutionized the medical area. Among
their application can be pointed out: lighting of
surgery rooms using surgical focus; source of
lighting which offers low level of photo biological
influence in closed environments, reducing
malfunctions in night workers and the “Jet-Lag”
effect; dermatological treatment for acne, psoriasis
Figure 2: Chart of the electrical (continuous arrow),
luminous (dashed arrow) and digital signals (dotted arrow)
in the system of the bilirubinometer.
and eczemas; phototherapy for the treatment of
jaundice; ultraviolet LED based disinfection systems
(Jones and Barnett, 2006). The programmable
photosensors which convert the light into frequency
in a sole CI operate with photodiodes matrix in
series with a current to frequency converter circuit.
The frequency of the signal out is directly
proportional to the incident light, and may be
connected to a microprocessor without the need of
any additional electronic or analogical to digital
converter. There are many laboratory and medical
applications using these ICs, such as low cost LED
based spectrophotometer (Yeh and Tseng, 2006) and
glucose meters (King, 2006).
3 RESULTS
130 measurements were analyzed based on 26
samples from different bilirubin concentrations,
besides their respective zero measurements, which
formed a data base for the Bilimed analysis. The
samples were collected in different newborns
hospitalized in the pediatric sector of the Clinical
Hospital of the Faculty of Medicine of Ribeirão
Preto - Brazil.
The obtained values were compared with the
value which was measured by using a commercial
bilirubinometer (Photo Ictometer OHC Model IV-
O’Hara & Co LTD) and by laboratory analysis
carried out in the pediatric laboratory of the same
hospital. From the collected data, 41 measurements
(30% of the results) have concentrations which is
greater than 10 mg/dl (171 μmol/dl). Figures 3 and 4
show the relationship of the concentration measured
by the Bilimed and the linearity of the results.
Electrical Sign
Optic Set
Microcontroler
Lenses and
Filters
Ultra
Bri
g
ht LED
455 nm
Photosensor
Signal Processing
LCD
Capillary Tube
575 nm
Pho
t
osensor
Drive
LED
Circui
t
Sensors
Reading
Switches
Re
g
ulated Source
Light Shaft Digital Data
Wavelenghts (nm)
420 460 500 540 580
1000
10000
100000
Molar Absorption (l/ mol)
Oxyhemoglobin
Bilirubin
BIODEVICES 2009 - International Conference on Biomedical Electronics and Devices
232
Figure 3: Graphic of the bilirubin concentration by the
concentration of the Bilimed, where the straight line is the
tendency found and the dots are the collected data.
0 5 10 15 20 25 30
0
5
10
15
20
25
30
Linearity
Reference bilirubin concentration (mg/dl)
Bilimed bilirubin concentration (mg/dl)
Figure 4: Linearity of the Bilimed equipment (dots) by the
reference (straight line).
Figure 5: Error in the measurement of the Bilimed
bilirubin concentration (points). The mean is equal to 0
mg/dl (dotted line), the double of the standard deviation is
2,093 mg/dl (dashed line), and the tendency line is shown
by the full line.
The reading error graph, generated by the
difference between the concentrations measured and
the reference ones, is shown on figure 5. The
statistical results on table 1 (standard deviation,
variance and maximum error) of the Bilimed
readings were also calculated.
Table 1: Standard deviation, variance and maximum error
found in the Bilimed reading.
Standard
Deviation
1,048 mg/dl (17,864 μmol/dl)
Variance 1,098 mg/dl (18,769 μmol/dl)
Maximum Erro
r
2,474 mg/dl (42,303 μmol/dl)
3.1 Result Analysis
There is a large linearity in the measurements
carried out by the Bilimed. Through the analysis of
the graph’s tendency curve of the bilirubin
concentration and of the signals sent by the
photosensors, the measurements are safe up to 30
mg/dl (513 μmol/dl), as for this value the absorption
of the 455 nm light shaft is still within the limit of
the photosensor reading error. Above this value the
luminous intensity and the signal become very low,
significantly increasing the reading error. The
equipment presents standard deviation of ± 1,05
mg/dl (± 17,1 μmol/dl), a result within the direct
bilirubin meters expectation. The maximal reading
error was 2,5 mg/dl (42,75 μmol/dl) for a
concentration of 23,5 mg/dl (401,85 μmol/dl). There
is a greater difficulty in obtaining samples with
values above this one, thus limiting the data base.
The main reasons for reading errors are related
to the temperature variations between the
measurements, the bad positioning of the capillary
tube in the holder, the bad separation of the serum in
the centrifugation process, and flaws and dirt in the
capillary tube.
In order to ensure the quality of the results it is
very important to follow the instructions correctly,
to carry out the measurement from zero before each
analysis, to avoid direct contact with the capillary
tube, and to centrifuge the sample so that a
homogeneous serum is obtained.
4 CONCLUSIONS
The measurement of the bilirubin concentration is a
very common procedure in hospitals and the
bilirubin meters are equipment which allow for a
quick evaluation of the patient’s condition. The
Bilirubin concentration (mg/dl)
Bilirubin concentration (mg/dl)
Diference
(
m
g
/dl
)
Reference bilirubin concentration (mg/dl)
Bilirubin measurement error
Bilirubin concentration
A LOW COST LED BASED BILIRUBIN METER - Description and Evaluation of a Low Cost Spectrophotometer
Bilirubin Analyzer
233
direct spectrophotometers have been in the market
for a long time and Bilimed has the same reliability,
accuracy and simplicity of these equipments.
In spite of the limited data base, the tests carried
out with the Bilimed equipment show an optimal
linearity in the result, with accuracy of 1mg/dl,
upper range limit of 30 mg/dl and strong co-relation
with the results obtained with the commercial
bilirubinometer used as reference. In order to assure
the reliability of the data, some procedures must be
used.
Bilimed offers technological improvements
contrasting with available devices. There is a strong
tendency in the use of LEDs to substitute high
intensity luminous sources. Due to the use of the
white ultra bright LED and special photosensors, the
size and the number of electronic components
involved in the project were reduced. Another point
that must be emphasized is the reduced production
cost and, as consequence, the final client price.
With the use of filters, lenses, LEDs and
photosensors, the Bilimed equipment can get to 20%
of the price of a transcutaneous bilirubinometer and
50% of a conventional bilirubinometer.
ACKNOWLEDGEMENTS
The authors sincerely thank Olidef cz, PE Lucio
Kimura and Prof. Dr. Arthur Lopes Gonçalves for
all the support.
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