Fluorescence is the ability to absorb light, then re-emit light at a longer wavelength. There are naturally occurring fluorescent molecules in the human body. Their fluorescence can be exploited to measure the molecules’ presence. Conventional fluorometers employ sample cells that require the light to be transmitted through the sample, not be highly absorbing, and not scatter the light. All of these rules are violated by blood. While fluorescent molecules can be extracted from samples, and concentrated, these steps are time consuming, require additional materials, increase the complexity, and could be damaging. It is better if measurements can be made on native samples.

The hematofluorometer was developed in the 1970’s at Bell Laboratories, a division of ATT. The hematofluorometer makes its measurement of the surface of blood, thus avoiding the problems conventional fluorometers experience. The first instrument commercialized measured the presence of Zinc Protoporphyrin (ZPP). This technology was licensed to Aviv Biomedical, Inc. Zinc protoporphyrin (ZPP) is a precursor in the synthesis of hemoglobin. When an individual is lead poisoned, or iron deficient, ZPP accumulates in the blood. As a result, the blood becomes slightly fluorescent. This device was approved by the US FDA, and has been available continuously.

Shortly after the development of the ZPP, it was found that bilirubin can also fluoresce. There are a number of different bilirubin species present. Only bilirubin that is bound to serum albumin will fluoresce at significant levels. This property forms the basis for a bilirubin binding assay. What distinguishes the hematofluorometer bilirubin assay from other bilirubin assays available in the US, is that it is a direct measure of bilirubin binding functionality.