DISCUSSION

The results of the present cross–sectional study on 87 cadavers indicated the statistically significant association between urinary morphine and biliary morphine, PCF, and CSF morphine with moderate agreement between urinary morphine and biliary morphine, and a weak agreement between urinary morphine and PCF, and CSF morphine.

There are various reasons that a cadaver must be studied for the presence of drugs, for instance, toxicity of opioids and blood samples are the gold standard sampling site (13). But in cases where blood samples are not available or accessible, other specimens should be selected, including urine, bile, CSF, and VH (14).

There are few studies that have evaluated the postmortem concentration of morphine in different body fluids and most studies have only focused on the comparison of one or two methods. One study showed higher drug concentrations in bile analysis than blood samples obtained from different sites (15), which is in line with the present study. Therefore, biliary specimens are an appropriate sample for assessment of morphine in cadavers. Also, other studies have indicated similar concentrations in PCF and blood samples for most drugs, especially morphine and its metabolites, and suggested PCF as a useful material for forensic toxicological assessment, when blood samples are not available (16, 17), which is consistent with the results of the present study, as there was a statistically significant association between PCF and urinary morphine, although the correlation was weak. Wyman and colleagues demonstrated highest morphine levels in liver, blood, CSF, and VH, respectively (12), which is similar to the results of the present study, indicating a statistically significant association between urinary and CSF samples, while this association was not statistically significant for VH. In another study, morphine and its metabolites was positive (>1 ng/ml) in 89% of urine samples, 68% of CSF samples, and 75% of VH cases (18), which was higher than the present study, indicating positive morphine in 48.3%, 5.7%, and 2.3% of urine, CSF, and VH samples. This difference can be due to the differences in the sampling technique, and measurement method. Holmgren and partners showed a significant difference between the concentrations in the VH and femoral blood for 23 substances and suggested VH an alternative specimen when blood samples are not available (19), while the results of the present study did not depict VH as an appropriate specimen, as there was no statistically significant association with urinary morphine, although in the study by Holmgren and colleagues, it was compared with blood sample, and was not specifically for morphine, which can justify the discrepancy between the results of the studies. The results of the present study on VH might be due to the inappropriateness of TLC method for analysis of morphine in VH, as studies have shown disposable pipette extraction (DPX) a fast, reliable, and easy to perform method for detection of drug abuse in VH with satisfactory sensitivity, precision, and accuracy (72–91%) (20), although TLC method, used in the present study, is an appropriate tool for forensic medical analysis of urinary opioids (21). In addition to the issues raised above, the interval between death and sampling also plays a significant role in the concentration of the drug, due to PMR phenomenon (6), which can justify the discrepancies among studies, as well. Thus, it is suggested that specimens should be selected individually for each case, based on the history and availability, while the procedures should be performed with proper quality (22), and post-mortem tissue/samples should be carefully selected, stored, preserved and utilized (23). Other studies have also assessed the tissue distribution of morphine and its metabolites in forensic medicine (24, 25), while the present research could suggest body fluids as an easy access method, especially bile, although further research is required on a comparison of the diagnostic accuracy of tissue versus fluids.

The main strength of the present study was a comparison of different sampling sites in one study in a referral Forensic Center that enables researchers with an appropriate spectrum, while most studies have only evaluated one or two methods (12, 16, 19). On the other hand, the present study had several limitations, such as limited sample size and cases of one Forensic Center that limits the generalizability of the results. In conclusion, the results of the present study showed that biliary measurement of morphine by TLC method could be an appropriate alternative for morphine detection in cadavers less than 72 hours after death when the urine sample is not accessible.