Detection of methaemoglobinaemia and its application in 'poppers' abuse: maintaining the right balance between reduction and autooxidation during storage.

In our study, we analysed the effect of a variety of storage conditions on the methaemoglobin (MetHb) content of blood samples obtained from altogether 110 deceased subjects with diverse causes of death, including three 'poppers'-related fatalities. The obtained results were compared to data from blood samples of six living, healthy subjects. Results obtained from the spectrophotometric measurement of blood MetHb content suggest that storage at room temperature (RT) and storage at -20 °C result in either highly fluctuating values, as was the case for the RT samples, or values much higher than the initial MetHb concentrations when stored at -20 °C. Blood samples at 4 °C showed more stable MetHb levels, which, however, increased with up to 4 % of the initial value after only 3 weeks of storage. These factors pose a problem in forensic toxicology, especially in nitrite abuse cases, where the involvement of such substance abuse is often unknown at the time of blood sampling and thus often requires longer storage times. Nevertheless, even after the storage of blood samples over several months at 4 and -20 °C, 'poppers' cases still show a significantly higher MetHb concentration as compared to non-'poppers' samples that were stored for the same time period under identical conditions.