What color is produced by the Jaffe reaction when creatinine reacts with the Jaffe reagent?

• A. Blue
• B. Red-orange tautomer
• C. Green
• D. Yellow

Answer: (B)

Creatinine reacts with picric acid in an alkaline medium to form a creatinine–picrate complex. This complex has a distinctive orange-red color, often described as red-orange, which is the color measured in the Jaffe colorimetric assay. The intensity of this red-orange hue increases with higher creatinine concentration, making it useful for quantifying creatinine levels. Colors like blue, green, or yellow do not come from this reaction, so they wouldn't be observed in the standard Jaffe test. The mention of a red-orange tautomer reflects the possible forms of the complex, but the observable color under typical conditions is the red-orange.