The major pitfall made by physicians who order toxicology screens is the assumption that the test is standardized. When one orders electrolytes in any hospital, one knows exactly what tests one will obtain. This is not true of toxicology testing. The analytic method used and the drugs identified are different in each hospital and are frequently determined by the pathologist. The clinician must be aware of the drugs that are able to be identified in that particular lab. Because a drug is not identified does not mean that the drug is not present. It may not be identified by the analytic method used in that hospital or it may be in such small concentrations in the blood or urine that testing will not identify it (ascendin, haldol).
In order for a test to be functional, it must be analytically valid, clinically reliable and applied correctly.
A toxicology screen is a combination of procedures aimed at identifying certain drugs. The screens may have different panels (coma, seizure etc). The gold standard for identifying the presence of a drug is confirmation by two different analytic methods. This usually takes time and in many hospitals, the tox screen is frequently a send out test. In order for the testing to benefit the clinical setting, the presumptive positives must be obtained in the hospital laboratory. Confirmation at a later time is more acceptable.
Next week: Part II
As always, if there are any questions, call the MTPC.
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