Determination of the serum creatinine concentration is widely used in the clinical evaluation of the patient with suspected renal disease. It provides an approximate estimation of the glomerular filtration rate and is a useful test, provided its limitations are appreciated. The method for determination of creatinine in the laboratory is based on the reaction described by Jaffe in 1886, namely, the development of a yellow or red color by the interreaction of creatinine and picric acid in an alkaline solution.1The presence in the serum of certain substances, usually called "chromogens," which give a similar color with picric acid, presents a problem in the determination and interpretation of the serum creatinine. Some of the chromogen substances are unknown. Others may include acetone, pyruvic and ascorbic acid, proteins, barbiturates, phenolsulfonphthalein, and sodium sulfobromophthalein. Their concentration varies with the method of deproteinization of the serum and the time allowed for development