[Is the assessment of serum creatinine reliable?]

Chemical and enzymatic methods are used to measure creatinine in serum and urine. Chemical methods are mostly based on the reaction of creatinine with alkaline picrate (Jaffe reaction). The Jaffe reaction is not specific for creatinine, the same reaction resulting in Jaffe-like chromogens show many interfering substances (ascorbic acid, bilirubin, proteins, ketones, cephalosporins and other drugs). Chemical and enzymatic methods show similar accuracy and day-to-day precision. Chemical methods are cheaper than enzymatic methods. Enzymatic methods require low sample volume and are not affected by the interfering substances as the chemical methods. Presented case report shows an unusual occurrence of drug interference in the enzymatic creatine deaminase procedure. Biological factors (circadian rhythm, pregnancy, hemodialysis, transplantation, stress, exercise), analytical and preanalytical factors (pH, glucose, pyruvate, bilirubin, fatty acids, sample storage and sample collection - gel tubes) and biological variability of creatinine play significant role in the creatinine examination.