abstract:The Jaffe reaction is a colorimetric method used in clinical chemistry to determine creatinine levels in blood and urine. In 1886, Max Jaffe (1841–1911) wrote about its basic principles in the paper Über den Niederschlag, welchen Pikrinsäre in normalem Harn erzeugt und über eine neue Reaction des Kreatinins in which he described the properties of creatinine and picric acid in an alkaline solution.