Blood storage for forensic hemoglobin analysis using CO-oximeter

Blood samples need to be stored for forensic examination using CO-oximeter in case immediate analysis is not possible at autopsy, or re-examinations are expected. In this study, we examined the condition for storage (temperature and air contact) to keep the initial values of hemoglobin derivatives unchanged for a long period. Fresh venous blood samples were divided into two groups; one group was stored without air and the other group with air headspace above the sample. The samples of each group were stored at 37 degrees C, room temperature (ca. 20-25 degrees C), ca. 4 degrees C and ca. -20 degrees C, respectively. They were analyzed with the use of CO-oximeter (CIBA-CORNING 270) a number of times during 6 weeks. And changes in the values of oxyhemoglobin (O2Hb), methemoglobin (MetHb), carboxyhemoglobin (COHb), deoxyhemoglobin (HHb) and total hemoglobin (THb) were examined. Also, another group of blood samples which were made high in COHb experimentally were stored without air at room temperature, ca. 4 degrees C and ca. -20 degrees C, and changes in the percentages of COHb of these samples were examined during 6 months. Our results indicated the following: When the purpose of storage is preservation of O2Hb, MetHb, COHb or HHb, storage at ca. 4 degrees C is considered appropriate, which can keep initial values for up to 2 weeks. As far as COHb is concerned, longer (at least 6 months) storage is possible at ca. 4 degrees C. And no contact with air is desirable in these storages. For THb, frozen storage may be best, which keeps the initial values for up to at least 4 to 6 weeks. In conclusion, when blood samples are stored for CO-oximeter analysis, the temperature and the period of storage should be decided according to the durability of each objective hemoglobin derivative.