The Jaffe reaction is a colorimetric method used in clinical chemistry to determine creatinine levels in blood and urine.

The color change that occurred was directly proportional to the concentration of creatinine, however he also noted that several other organic compounds induced similar reactions.

[5] He was promoted to director of the Laboratory for Medical Chemistry and Experimental Pharmacology in 1878 and became a member of the Deutsche Akademie der Naturforscher Leopoldina in 1882.

[6] Jaffe had noticed that, when mixed in a sodium hydroxide (NaOH) solution, picric acid and creatinine formed a reddish-orange color and needle-like crystal precipitate.

[8] Although he found the amount of precipitate directly proportional to the creatinine concentration, he also noted that the reaction was highly nonspecific and could be observed with many other organic compounds.

[10] He took advantage of technology available at the time, using a Duboscq colorimeter for measurement precision, and is credited for introducing colorimetry into modern biochemical analysis.

[1] Diabetes patients are a high-risk population to develop chronic kidney disease (CKD) and, therefore, interferences from glucose and acetoacetate are of particular importance.

[1] Before Jaffe, Neubauer described a similar precipitation reaction by mixing creatinine with zinc chloride (ZnCl2) and performing a Weyl's test—the addition of SNP to NaOH and then incubating with acetic acid (CH3CO2H) to develop a color change.

As Folin's method evolved, various techniques were implemented to remove Jaffe-reacting substances, mostly protein, from the sample and increase specificity.

[1] Kinetic Jaffe methods involve mixing serum with alkaline picrate and reading the rate of change in absorption spectrophotometrically at 520 nm.

[15] High-performance liquid chromatography, HPLC, was more sensitive and specific, and had become the new reference method endorsed by the American Association for Clinical Chemistry.

[2][15][17] HPLC addressed the shortcomings of Jaffe-based methods, but was labor-intensive, expensive, and therefore impractical for routine analysis of the most frequently ordered renal analyte in medical labs.