Endogenous cutoff levels

The validity of these theoretically determined cutoff levels was evaluated by the various field studies described below. In some of these this involved comparing the results of hair analysis to those of urinalysis and self-reports. In the case of cocaine and morphine the validation of endogenous cutoff levels involved also the controlled administration of these substances. - With morphine this was done with poppy seed and involved a comparison of hair and urine results. These experiments clearly demonstrated the greater effectiveness of the endogenous cutoff levels used by hair analysis, for all attempts to exceed the opiate cutoff level of hair analysis by the massive ingestion of poppy seeds failed. In contrast to this, the cutoff level of urinalysis was exceeded by wide margins. That this particular problem of urinalysis is not unique to poppy seeds has been demonstrated experimentally by Baselt and Change in the case of cocaine. 

In contrast to the single laboratory safeguard of urinalysis against its main problem, i.e., the endogenous cutoff level, hair analysis is favored by many protective... 

If one now adds to these safety features against exogenous false positives the ability to collect a second hair sample, safer endogenous cutoff levels, the trilevel reporting system (negative, contaminated, or positive), as well as the subversion-proof nature of the hair test, one can readily appreciate that hair analysis is a safer procedure than urinalysis. One also recognizes that hair analysis, unlilce urinalysis, is not a stand-alone test. 

The nature of our concern is best illustrated by a specific example. Blank and Kidwell use a cocaine solution of 100,000 ng/mL for their contamination experiments, to which they add approximately 1 pCi of tritium-labeled cocaine, i.e., approximately one million counts per minute. Therefore, they have approximately a sensitivity of 10 cpm/ng of sample. Decontamination of hair means that residual drug concentration must drop below the endogenous cutoff level of 5 ng/10 mg of hair, i.e., to 50 cpm/10 mg hair. Now if the labeled cocaine has a radiochemical impurity of as little as 0.1%, this corresponds to 1000 cpm or to 100 ng of residual cocaine equivalents. Since self-irradiation of tritium-labeled material tends to form polymeric impurities, and since these are likely to preferentially bind to hair, one incurs a major risk of concluding erroneously that the residual radioactivity represents residual cocaine contamination rather than contamination by polymeric degradation products. 

Even though the majority of results were below the adult endogenous cutoff level (not to mention the tenfold higher cutoff level for children) and in spite of the presence of benzoylecgonine which indicated passive exposure. Smith and KidwelPi drew the erroneous conclusion that our wash kinetic criteria failed to... 

Drug Intake Required to Produce Hair Drug Levels at the Cutoffs Set as Protection against Passive Endogenous Drug Exposure "... 

The concentrations of the internal standards are prepared such that the key metabolites are at approximately the same concentration as the median endogenous metabolite concentrations, at the concentration of the decision point for normal or abnormal, or at the concentrations of similar metabolites. For example in one set of AC standards, the relative concentration of the AC internal standards FC C2 C3 C4 C5 C8 C14 C16 is 20 5 1 1 1 1 1 2. There are many ideal approaches for setting the concentrations of internal standards. The reason for the choice above was that for many ACs, the endogenous concentrations are very low at or below the signal-to-noise ratio for detection. The internal standards were set to be close to the cutoff for abnormal/ normal and at a similar concentration to other standards. Further, keeping these relative concentrations is helpful in the interpretation and harmonization of the assay as they have been used for many years and in several publications. Amino acids are at concentrations more closely similar to endogenous levels rather than the same concentration of other amino acid standards. 

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