Zur präanalytischen Phase chemisch-toxikologischer UntersuchungenI. Immunochemisches Drogenscreening im Urin – Erkennbarkeit von Manipulationen und Strategien bei rechtsmedizinischer Fragestellung

The significant legal and ecomonic ramifications of a positive drug test produce an incentive among users of illicit drugs to escape detection. Therefore, being the easiest body fluid to handle for drug screening urine is very often manipulated to test clean. Methods available to cause a negative result range from substitution of urine, adulteration of the collected specimen by various chemical agents and in-vivo manipulations. Among these, the preferred strategy is to increase fluid intake and urine flow so as to dilute the concentration of drugs below the threshold of detection. To determine the extent of possible specimen dilution the urinary creatinine concentration is generally determined. Based on data from uncontrolled and controlled fluid intake studies in the literature and physiological conditions of urinary excretion, the meaningfulness of creatinine concentration in randomly obtained urine samples is discussed. A low creatinine concentration not clearly proving an intentional dilution of the sample, the application of GC/MS analysis or the concentration of the urine prior to drug screening is recommended for specimens exhibiting a “suspect” urinary creatinine concentration.