Among many laboratory tests for supporting a conclusion of death by drowning, the diatom test is often regarded as the gold standard. However, opinions are divided on its usefulness, and thus this test is rarely or never applied in some countries or institutions. Indeed, even when characteristic macroscopic findings of drowning are weak, drowning can often be reasonably concluded as a cause of death by taking circumstantial evidence into consideration and carefully excluding other causes. However, incorporation of the diatom test will further increase the certainty of such a conclusion. When highly decomposed corpses are found in and near water environments, autopsy findings are of limited value, and the cause of death often remains undetermined. However, death that could have been due to drowning in some decomposed corpses can be assumed if the results of diatom testing are interpreted as positive. Pollanen illustrated the contribution of the diatom test to conclude drowning as a means of homicide in a presentation of six cases. The largely burned remains of a teenage girl were found in a parking lot where accelerant was detected. The results of an autopsy did not indicate the anatomical cause of death. However, 5 mL of watery fluid was aspirated from the right maxillary sinus. Over ten types of diatoms were detected in the fluid, and four of them that were also detected in bone marrow established drowning as the cause of death. Many forensic pathologists in Japan rely more or less upon the diatom test and consider that concluding or ruling out drowning as a cause of death is insufficient without a diatom test. We also believe that the diatom test is indispensable, and this chapter principally examines the advantages and disadvantages of this test from that perspective. Recent approaches to supporting a conclusion of death by drowning have been tabulated, and a simple measurement of the electrolyte concentration in pleural effusions has been introduced. In addition, microbiological tests conducted by ourselves and others are described, despite their experimental nature.
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