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

 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

ht LED

455 nm

Photosensor

Signal Processing

LCD

Capillary Tube

575 nm

Pho

osensor

Drive

LED

Circui

Sensors

Reading

Switches

ulated Source

Light Shaft Digital Data

Wavelenghts (nm)

420 460 500 540 580

1000

10000

100000

Molar Absorption (l/ mol)

Oxyhemoglobin

Bilirubin

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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

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

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)

Diference

(

/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.

REFERENCES

Askin, D. F. & Diehl-Jones, W. L. (2003) The Neonatal

Liver, Iii: Pathophysiology Of Liver Dysfunction.

Neonatal Network, 22, 5 - 15.

Bhutani, V. K., Gourley, G. R., Adler, S., Kreamer, B.,

Dalin, C. & Johnson, L. H. (2000) Noninvasive

Measurement Of Total Serum Bilirubin In A

Multiracial Predischarge Newborn Population To

Assess The Risk Of Severe Hyperbilirubinemia.

Pediatrics, 106.

Diamond, L. K. (1970) A History Of Jaundice, Baltimore,

Willians And Willians.

Du, H., Fuh, R. A., Li, J., Corkan, A. & Lindsey, J. S.

(1998) Photochemcad: A Computer-Aided Design

And Research Tool In Photochemistry.

Photochemistry And Photobiology, 68, 141–142.

Grohmann, K., Roser, M., Rolinski, B., Kadow, I., Müller,

C., Goerlach-Graw, A., Nauck, M. & Küster, H.

(2006) Bilirubin Measurement For Neonates:

Comparison Of 9 Frequently Used Methods.

Pediatrics, 117, 1174-1183

Jackson, S. H. (1961) A Simple Stable Instrument For

Determination Of Bilirubin By Direct

Spectrophotometry. Clinical Chemistry, 7.

Jones, G. & Barnett, G. (2006) High-Power Leds Provide

Illumination And Treatment In Medical Applications.

Leds Magazine.

King, R. (2006) Optoelectronic Sensors In Medical

Applications. In (Taos), T. A. O. S. (Ed.) Sensors.

Knudsen, A. (1989) Prediction Of The Development Of

Neonatal Jaundice By Increased Umbilical Cord Blood

Bilirubin. Acta Paediatrica Scandinavica, 78, 217-21.

Maisels, M. J. (2006) Historical Perspectives:

Transcutaneous Bilirubinometry. Neoreviews, 7, 217-

225.

Odell, G. B. (1980) Neonatal Hyperbilirubinemia, Grune

& Stratton.

Roggan, A., Friebel, M., Dörschel, K., Hahn, A. & Müller,

G. (1999) Optical Properties Of Circulating Human

Blood In The Wavelength Range 400–2500 Nm.

Journal Of Biomedical Optics, 4, 36-46.

Taksande, A., Vilhekar, K., Jain, M., Zade, P., Atkari, S.

& Verkey, S. (2005) Prediction Of The Development

Of Neonatal Hyperbilirubinemia By Increased

Umbilical Cord Blood Bilirubin. Current Pediatric

Research, 9, 5-9.

Yeh, S. & Tseng, S. S. (2006) A Low Cost Led Based

Spectrometer. Journal Of The Chinese Chemical

Society, 53, 1067-1072.

Zijlstra, W. G., Buursma, A. & Roest, W. P. M.-V. D.

(1991) Absorption Spectra Of Human Fetal And Adult

Oxyhemoglobin, De-Oxyhemoglobin, Carboxy-

hemoglobin, And Methemoglobin. Clinical Chemistry,

, 1633-1638.

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