Considerations in the interpretation of urine analyses in suspected opiate intoxications

Over the years, it has been observed that in many suspected opiate intoxications, a urine screen using the standard 300 ng/mL cutoff has produced negative results. Subsequent analysis of the blood in many of these cases, in fact, were positive for morphine. To identify the frequency of this occurrence and to determine a more appropriate urine screening cutoff, paired blood and urine specimens were tested for opiates at the above cutoffs. Over the 6 months period of this study, 102 cases were identified where the blood morphine concentration by Roche Abuscreen was greater than 100 ng/mL of "morphine equivalents." All positive cases were confirmed as morphine by gas chromatography-mass spectrometry. Seventy nine of these cases, or 77%, had urine concentrations by Abuscreen exceeding 300 ng/mL of "morphine equivalents." The remaining 23 cases had urine morphine concentrations less than 300 ng/mL by Abuscreen. Urine specimens were then reanalyzed by Abuscreen using dilutions of the 300 ng/mL calibrator: 50, 75, and 150 ng/mL. Even with the use of a 50 ng/mL cutoff, 9 of these 23 specimens tested negative by Abuscreen. Moreover, 23 of the 67 cases or 34% in which the cause of death was narcotic intoxication had urine opiate concentrations by Abuscreen less than the recommended 300 ng/mL cutoff. These results indicate the critical importance in cases of suspected narcotic intoxication of screening the blood in addition to urine.