Selection And Collection Of Specimens For Analysis

Specimens for biochemical and toxicological analysis must be retrieved, labeled, stored, and analyzed under established, standardized conditions (3). In most cases, the time of sample procurement is the documented time of autopsy. For this reason, the recorded time of autopsy should be the time that the internal examination is commenced. If a postmortem sample is drawn either before or after the internal autopsy examination, the time of procurement should be separately noted. Interpretation of postmortem chemistry is also enhanced by the routine recording of early putrefactive changes.

BLOOD This is the substrate of choice for testing for hemoglobin S, hormones, cholinesterase, and abnormal metabolites in infants with suspected inborn errors of metabolism. Blood can be used to measure the concentrations of creatinine, urea nitrogen and bilirubin if vitreous, the specimen of choice, was not procured. All postmortem serum or plasma samples have some degree of hemolysis, and laboratories differ in their tolerance for specimens of this type. As a practical matter, the autopsy pathologist ordinarily need not be concerned with the distinction between plasma and serum; the laboratory separates the red cell mass from the supernatant and labels it as it sees fit. Postmortem concentrations of many analytes vary considerably with the anatomic locations of the sampling sites. Unlike the situation with postmortem toxicology, this variation has not been well-studied for endogenous substances, with the exception for glucose, for which the sample of choice is vitreous, rather than blood. The sampling and labeling policies required for toxicologic analysis are more than adequate for postmortem chemical analysis. The choice of container is dictated by the test to be undertaken, as in clinical testing. A common screening panel for inborn errors of metabolism requires three drops of blood on a filter paper.

VITREOUS This is the most frequently used specimen for postmortem chemical analysis. Typically, a panel of six tests is run, comprising sodium, potassium, chloride, urea nitrogen, creatinine, and glucose. Bilirubin may be added to the panel if

Table 11-1

Common Changes of Postmortem Chemical Valuesa

Table 11-1

Common Changes of Postmortem Chemical Valuesa

Substancesb

Body fluids

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