A urine screening study reported overall agreement from 92.4% to 100% between an immunoassay and a mass-spectrometry method. To interpret that range, examine the positive and negative specimens available for each drug.
The study tested 105 urine specimens. Some drug classes had discordant results. For cocaine, methadone and phencyclidine, no positive clinical specimens were available to assess positive agreement. Agreement among negative specimens could still be high when positive-case performance remained untested.
Separate experiments examined responses near the screening cutoffs, where repeated tests could produce both positive and negative results. A negative screen therefore cannot establish that no drug is present. For an individual result, identify the analyte, cutoff, specimen and whether a suitable confirmatory method was performed.