Blood is widely regarded as the specimen offering the best correlation between drug levels and likely dosing and likely concomitant pharmacological, cognitive, and psychomotor effects. There have been many controlled dosing studies examining blood levels of drugs and concomitant effects. However, owing to ethical concerns, not all abused drugs have been subjected to such controlled dosing studies. Drug levels found in blood are often quite low (ng/mL) and often short-lived. The analysis of drugs in blood is time-consuming, generally requiring extraction procedures before further analyses can be performed. There have been several publications addressing the application of urine immunoassays to the analysis of blood specimens, after appropriate extraction protocols (6,7).

Although blood is widely used for drug testing in clinical and emergency toxicology settings, especially for alcohol, the invasiveness of the collection of blood specimens does not lend itself to routine testing in other nonclinical contexts, such as in workplace-, student-, and corrections-testing environments. Furthermore, there is much greater risk of transmission of infectious disease through handling of blood specimens than with many other routinely tested specimens for drugs-of-abuse testing. Accordingly, blood will not be further considered in this review.

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