Which reagent is used in the colorimetric Jaffe method for creatinine determination?

• A. Saturated picric acid + 10% NaOH
• B. Sodium nitroprusside
• C. Sodium hypochlorite
• D. Sulfuric acid

Answer: (A)

In the Jaffe colorimetric method, creatinine reacts with picric acid under strongly alkaline conditions to form a red-orange creatinine-picrate complex, whose color intensity reflects the creatinine concentration. This requires saturated picric acid in an alkaline medium, commonly with NaOH. The other substances don’t produce this chromogen for creatinine measurement: sodium nitroprusside detects ketone bodies, sodium hypochlorite is a general oxidizer used in other assays, and sulfuric acid alone doesn’t create the Jaffe chromophore.