An investigation into the extent of possible dilution of specimens received for urinary drugs of abuse screening.

Recent American and Swedish studies have shown an increase in "false" negative results when analysing dilute urine specimens for drugs of abuse. In the light of these studies, it was decided to perform a pilot study to determine the extent of possible specimen adulteration and dilution in a random batch of 50 urine specimens presented to this laboratory, using creatinine, osmolality, pH and relative density. It was found that 20% of the specimens were outside the pH range associated with the optimum working of Syva EMIT Drugs of Abuse in Urine (DAU) immunoassay screening techniques, and that if the National Institute on Drug Abuse (NIDA) recognized dilution cut-off of 1.8 mmol/L for urine creatinine concentration is applied, 84% of the specimens surveyed here would need to be repeated to ensure accurate results. Because of these findings, it is recommended that routine creatinine and pH estimations should be performed on all specimens submitted for urinary drugs of abuse screening, or at least when unexpectedly negative results are obtained.