Henry Ford Hospital, "Performance of the RDS Drug Screen"
The RDS drug screen from American Biomedica Corporation was evaluated and compared to the Syva Emit and the Triage from Biosite. The test was easy to use and interpretation of results was very clear. No measuring of samples was necessary to perform the test. A total of 158 patient samples and 46 "spiked" samples were analyzed by all three methods. All positive PCP samples, 20 of the positive methamphetamine samples and 5 of the positive amphetamine samples were negative urine samples spiked with the indicated drug. If any of the three results disagreed, the samples were sent to a reference laboratory for confirmation. The results are sumarized as follows:
Cocaine
There were 89 negative samples and 28 positive samples. There was complete agreement with all three methods.
THC
There were 80 negative samples and 28 positive samples. All three methods agreed on negative and positive results.
Opiates
Of 89 negative samples and 27 positive samples all were identified correctly by the Triage. Both Syva and RDS identified one negative sample as positive.
Barbiturates
There were 86 negative samples and 22 positive samples all identified correctly by Triage and RDS. The Syva emit did not detect 3 of the positives.
Benzodiazipines
There were 91 negative samples and 22 positive samples. Syva detected all positives but also classified two negative samples as positive for a specificity of 97% and accuracy of 98%. Triage correctly classified all negatives but failed to detect two positives for a sensitivity of 91% and accuracy of 98%. RDS had one false negative and one false positive resulting in sensitivity of 95%, specificity of 99% and accuracy of 98%.
Amphetamine/Methamphetamine
Assesment of this classification was somewhat more complicated because the Syva Emit is an SMA Screen, the Triage detects both amphetamine and methamphetamine, and the RDS has separate assays for amphetamine and methamphetamine. There were 113 samples that were negative by all three methods. Of 31 samples known to have amphetamine, all were positive by the SMA screen (Syva), all were positive by the Triage and 26 were positive by the RDS. Three of the samples missed by the RDS screened positive for methamphetamine even though no methamphetamine was present. Four samples containing methamphetamine screened negative for amphetamine class with Triage. One sample known to contain methamphetamine screened negative by RDS. Calculating accuracy is somewhat subjective for this classification. Three of the missed amphetamines using the RDS panel would have still been labled suspicious by the methamphetamine assay. Given that methamphetamine is rarely seen and given the confusing results, one could question the value of having a separate screen for both classes.
PCP
Of 20 samples spiked with PCP, all tested positive with the Syva Emit and the Triage. One sample screened negative with RDS.
Conclusion
The RDS drug screen overall is comparable to Triage. It has better sensitivity to barbiturates than does Syva Emit and is superior to Triage in the detection of methamphetamine. It could be used to replace the Triage in settings where the detection of tricyclics is not an issue.
