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The bile pigment bilirubin is the major end product of the breakdown of heme in the liver. It is excreted in bile and urine. Its yellow color is responsible for the yellowish appearance of patients with jaundice.

In 1847, German scientist Rudolf Virchow and his colleagues isolated bilirubin crystals from hematomas and conjectured that it was derived from blood. More than a century later, Irving M. London and co-workers at Columbia University demonstrated that heme is indeed its source.

The central structure of heme is a porphyrin ring. Bilirubin’s structure is that of a ring-opened porphyrin: a chain of substituted pyrrole and 1,3-dihydro-2H-pyrrol-2-one rings.

The determination of bilirubin concentrations in blood is a key test for diagnosing medical conditions such as hepatobiliary or heart disease. Traditionally, blood tests have been performed in laboratories and can take several hours to complete. Patient-operated finger-stick tests with appropriate analytical equipment theoretically would take less time and be less expensive. But the recent Theranos debacle showed that . Improvements in biosensors, sampling methods, and other factors are necessary to make this method practical.