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Validity of toxicological data

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  p34-35

2026-09-15

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Validity of toxicological data

A number of physical factors affect the validity of toxicological findings. Paramount are the accuracy of the analytical tests conducted and the nature of the specimen used. Blood and urine are the most commonly used specimens for analysis, although blood drug concentrations are generally considered to provide the best possible estimate of the likely pharmacological responses. Urine is an excretory fluid, and while it is useful for detection of drugs and metabolites, it does not necessarily provide an indication of the likely effect of a drug on the body. In postmortem cases the origin of a blood sample must be stated and the sample should preferably be obtained from peripheral sites, such as the leg (femoral vein) or arm (subclavian vein), as blood from central parts of the body can have very different drug concentrations (see section on postmortem redistribution below). When a toxic response to a drug (or drugs) is suspected, it is advantageous to measure the drug concentration in two or more independent samples; the value of a result from a single sample is limited unless the distribution of the drug is known. This could be from two peripheral blood samples or from a peripheral blood and a liver specimen. Tissues that selectively take up a particular drug may have a much higher concentration than that found in blood. For example, 11 carboxytetrahydrocannabinol has high concentrations in fat; digoxin and other cardiac glycosides are taken up by cardiac muscle; biliary concentrations of drugs excreted from the liver as glucuronides (e.g. morphine) are usually considerably higher than their concentrations in blood.

In addition to being distributed unevenly throughout the body, a drug may not be distributed evenly within the separate parts of a single tissue (see section on blood and plasma concentrations above). In blood, drugs may tend to be concentrated either in the plasma or in the erythrocytes. Thus, it may prove to be of little value to examine a plasma sample in a case where the drug involved is known to be concentrated in the red blood cells (e.g. acetazolamide).