Specimen types
Other fluids, tissues and organs
Bile has been collected historically, although its usefulness is limited. Previously, bile was valu able because it contains high concentrations of drug conjugates, most notably morphine. Detection of morphine and many other drugs (e.g. benzodiazepines, colchicine and buprenorphine) is, therefore, more likely in the bile than in the blood, in which concentrations may be as much as 1000 times lower. The possibility that drugs in the bile may undergo enterohepatic re-circulation should not be overlooked. With the widespread use of sensitive immunoassays and other techniques, the use of bile as a screening specimen is therefore less valuable than it once was. In addition, bile, like urine, is a waste fluid and, with the possible exception of ethanol, the correlation between blood and bile concentrations of drugs is generally poor.
Brain, kidney and spleen have been used to determine and interpret the concentrations of drugs or other toxins. Brain, and indeed other organ tissues, can be useful in assessing the overall body burden of the drug, although the database of reference values that may assist interpretation is limited. The brain offers the additional advantage that it is a relatively isolated organ and should be unaffected by trauma to the abdomen and chest, although concentrations of many drugs may vary from one region of the brain to another. The measurement of drugs in the brain may therefore be misleading unless the origin of the tissue analysed is identified and there is an adequate database regarding concentrations in that anatomic region.
Drug concentrations in the kidney and spleen have little intrinsic significance, other than as part of the overall assessment of the body burden of a toxin, although the kidney has been found to be useful in determining heavy metal concentrations. Spleen has been used as a secondary specimen for toxins, such as carbon monoxide and cyanide, that bind to haemoglobin.
