Originally Published June 2000

Bilirubin Analyzer Uses Light Touch to Test for Jaundice among Infants

Rugged, compact microspectrometer is key component in noninvasive device.

Norbert Sparrow, Editor

A majority of newborns require at least one blood test for jaundice. This is typically done by lancing the heel of the infant and measuring the total serum bilirubin levels in the drawn blood. Not only is the procedure painful, but the results may be inaccurate. Studies have shown that clinical methods for measuring total serum bilirubin can vary by more than 17% within and across laboratories. Noninvasive bilirubin analyzers eliminate the need to draw blood while producing more-accurate results. These devices rely on miniature spectrometers to quantify the optical spectrum reflected from an infant's head.

A noninvasive analyzer developed by SpectRx (Norcross, GA) measures total serum bilirubin levels by directing white light onto the skin of the newborn and measuring the intensity of the reflected wavelengths. A spectrometer divides the reflected light into wavelength bands and measures the strength of each band. The intensity of the various wavelengths is then analyzed by a microprocessor to generate bilirubin measurements. A study of 1043 babies showed the optical analyzers to generally be more accurate than traditional tests, according to Vinod K. Bhutani, MD, professor, section of newborn pediatrics, Pennsylvania Hospital (Philadelphia).

Right: A noninvasive bilirubin analyzer developed by SpectRx eliminates the need to draw blood from most infants to test for jaundice.
Left: This microspectrometer, manufactured by microParts and distributed in the United States by American Laubscher, measures the intensity of light reflected from an infant's forehead to determine total serum bilirubin levels.

"The technology involved in this type of device is quite well known," says SpectRx senior product engineer Greg Newman. The real challenge, he adds, was designing a device that would provide the required level of accuracy while being suitably compact and rugged for use in a newborn ward or a patient's home. "We needed a product that was small enough to fit into a nurse's hand and even into the entrance of an isolet," says Newman. It also had to be sufficiently rugged to withstand a 4- to 5-ft drop without affecting the accuracy of the test results, he added. "The most critical component of an optical analyzer is the microspectrometer," says Newman. The company evaluated a wide range of meters from manufacturers around the world; the company opted for one that is manufactured by the microParts Div. of Steag AG, headquartered in Dortmund, Germany. It is distributed in the United States by American Laubscher Corp. (ALC; Farmingdale, NY).

Component Survives 4-ft Drop

The component measures 2½ x 1½ x 3/8 in., about half the size of the next-smallest comparable device, according to Newman. "It also proved to be very rugged," he adds. "Early in our evaluation process we put the microspectrometer in a simple package and dropped it onto a tile floor from a height of 4 ft. It passed this test with flying colors. In fact, potential customers told us that a competitive analyzer based on optical filter technology required repairs nearly every time it was dropped," says Newman.

The ALC meter is constructed of three layers of PMMA, the center layer of which contains the diffraction grating, a fiber alignment groove and a mirror that reflects the spectrum onto a photodiode array. The input is a 105 x 125-µm step index glass fiber, while the optical output is based on a 256-pixel photodiode array. The grating dispersion of 0.12 nm/µm leads to a pixel dispersion of approximately 3 nm/pixel that is linear over the entire spectral range.

The ALC meter covers the entire visible 380–780-nm spectral range, another advantage it has over components based on optical filter technology, according to Newman. "Optical filter instruments are only capable of making measurements at a few discrete wavelengths," says Newman. "Being able to make full-scan measurements enabled us to avoid revising the instrument during the prototype stage as the algorithm was perfected. Being able to skip these design modifications helped us to bring the product to market 9 to 12 months faster," he notes.

Blended Technology Brings Down Costs

The ALC meter is manufactured using LIGA technology, an acronym for the German words for lithography, electroforming, and molding, the processes that constitute this novel manufacturing method. Its primary advantage is to bring down production costs on high-quantity products.

A master structure is made by exposing a polymer resist to highly energetic and parallel synchrotron radiation. The polymer resist carries a gold absorber mask, which duplicates the top view of the final component. The finished resist—a 3-D projection of the mask structure—is transferred onto metal by means of electroforming. The resulting solid metal block carries the exact negative of the master structure; it serves as a mold insert that can then be used to produce the final product either by injection molding or embossing. In this particular case, the meter is manufactured by embossing the structure onto PMMA foil.

SpectRx estimates that noninvasive monitors can eliminate the need for blood samples among about 85% of newborns. The accuracy of these devices will allow more-precise monitoring of jaundice, thereby reducing the number of infants needing to receive phototherapy, adds Bhutani.

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