Nucleated Red Blood Cells As a Marker of Hypoxia in SIDS
Nucleated Red Blood Cells As a Marker of Hypoxia in SIDS
nRBCs are not present in the peripheral blood of normal and healthy individuals beyond the neonatal period. Their presence in the peripheral blood in these circumstances would indicate that they have either been recruited from the bone marrow or that extramedullary haematopoiesis has occurred. There are many pathological processes whereby their levels would be increased including anaemia, bone marrow disorders, splenic pathology and pathological extramedullary haematopoiesis but they are also increased in other situations such as hypoxic states, certain metabolic disruptions, sepsis and iatrogenic interventions.
A thorough postmortem investigation in our cases excluded any pathological process in the groups A–C. Our results did not show that the level of nRBCs in peripheral blood could be used as a marker of hypoxia to help categorise deaths in the classification proposed by Randall et al. Our results, however, demonstrated that nRBCs in peripheral blood were significantly increased (p=0.0001) in Group E with respect to groups A and B and in infants born prematurely (p=0.02). The increment of nRBCs in premature infants was particularly significant for groups B and E at 24–34 weeks (p<0.05) and for group E in those born at 35–37 weeks. In addition, we found higher nRBCs (p=0.09) in the cases with maternal smoking in pregnancy and at younger ages (0–4 and 5–12 weeks; p=0.002) for all categories of death.
A reliable, robust and repeatable laboratory test to detect antemortem hypoxia is yet to be identified. Although several biochemical tests have been considered as potential markers of hypoxia (including serum lactate, vitreous hypoxanthine and levels of vascular endothelial growth factor in the cerebrospinal fluid), none have yet proved to be reliable enough.
Our study showed that the level of nRBCs in the peripheral blood is not useful to categorise a death as asphyxial (category B of Randall et al classification). The most reliable evidence to document asphyxia is still based on clinical history and scene investigation for unsafe sleeping environments such as wedging/overlaying. Our results show that levels of nRBCs are greatly increased in those patients where the cause of death was due to an underlying chronic condition (Group C) or illness, trauma or suffocation (Group E).
Parental smoking is considered a risk factor for SIDS, although the exact mechanism for this has not been proved. Our study confirmed that babies exposed to maternal tobacco during pregnancy had higher levels of nRBCs. Whether this is related to exposure to a hypoxic environment is yet to be determined.
Among the limitations of our results were the facts that we did not have an age-matched control group of healthy, live babies and that the identified variables have had an impact on our values in a manner not yet understood. The clinical history provided to the pathologist significantly influences the final category of death assigned to the case.
Discussion
nRBCs are not present in the peripheral blood of normal and healthy individuals beyond the neonatal period. Their presence in the peripheral blood in these circumstances would indicate that they have either been recruited from the bone marrow or that extramedullary haematopoiesis has occurred. There are many pathological processes whereby their levels would be increased including anaemia, bone marrow disorders, splenic pathology and pathological extramedullary haematopoiesis but they are also increased in other situations such as hypoxic states, certain metabolic disruptions, sepsis and iatrogenic interventions.
A thorough postmortem investigation in our cases excluded any pathological process in the groups A–C. Our results did not show that the level of nRBCs in peripheral blood could be used as a marker of hypoxia to help categorise deaths in the classification proposed by Randall et al. Our results, however, demonstrated that nRBCs in peripheral blood were significantly increased (p=0.0001) in Group E with respect to groups A and B and in infants born prematurely (p=0.02). The increment of nRBCs in premature infants was particularly significant for groups B and E at 24–34 weeks (p<0.05) and for group E in those born at 35–37 weeks. In addition, we found higher nRBCs (p=0.09) in the cases with maternal smoking in pregnancy and at younger ages (0–4 and 5–12 weeks; p=0.002) for all categories of death.
A reliable, robust and repeatable laboratory test to detect antemortem hypoxia is yet to be identified. Although several biochemical tests have been considered as potential markers of hypoxia (including serum lactate, vitreous hypoxanthine and levels of vascular endothelial growth factor in the cerebrospinal fluid), none have yet proved to be reliable enough.
Our study showed that the level of nRBCs in the peripheral blood is not useful to categorise a death as asphyxial (category B of Randall et al classification). The most reliable evidence to document asphyxia is still based on clinical history and scene investigation for unsafe sleeping environments such as wedging/overlaying. Our results show that levels of nRBCs are greatly increased in those patients where the cause of death was due to an underlying chronic condition (Group C) or illness, trauma or suffocation (Group E).
Parental smoking is considered a risk factor for SIDS, although the exact mechanism for this has not been proved. Our study confirmed that babies exposed to maternal tobacco during pregnancy had higher levels of nRBCs. Whether this is related to exposure to a hypoxic environment is yet to be determined.
Among the limitations of our results were the facts that we did not have an age-matched control group of healthy, live babies and that the identified variables have had an impact on our values in a manner not yet understood. The clinical history provided to the pathologist significantly influences the final category of death assigned to the case.
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