We read with great interest the “Update: Cold Weather Injuries Among the Active and Reserve Components of the U.S. Armed Forced, July 2018-June 2023.”¹ While the update provides valuable insight into the relative number of cold weather injuries incurred by military personnel across the last five years, the authors incorrectly stated that the latest 2023 update to Training and Doctrine Command (TRADOC) Regulation² recognizes sickle cell trait as a risk factor for cold injury. Current TRADOC policy does suggest SCT screening, driven at least in part by an increased risk of exercise collapse associated with sickle cell trait, exertional rhabdomyolysis, and blood clots in austere hot and hypoxic environments.² Yet, no specific policy language exists linking the presence of SCT to the risk or occurrence of cold weather injuries.

SCT is a condition that involves the presence of a mutation on 1 of 2 genes that form red blood cells, while the complementary gene remains unmutated. Because it is typically a benign carrier condition, SCT does not disqualify carriers from military service. Very little data currently exist to support a convincing link between cold weather injuries including hypothermia, freezing injury, or non-freezing cold injury and the presence of SCT. Data from the early 1950s suggests the incidence of frostbite in a small subset of African Americans, who present day tend to disproportionately carry SCT at a rate of 73.1 cases per 1,000 compared to 6.9 in Hispanics and 3.0 in non-Hispanic Whites,³ did not appear greater in those with SCT compared to non-SCT controls.⁴ This very limited sample by no means speaks to a lack of association between SCT and cold injury or cold thermoregulatory adjustments. Undoubtedly there is a profound need to further leverage epidemiological data to improve our understanding of cold injury risk in those with SCT. Additionally, human experimental data is needed to determine if cold thermoregulation in those with SCT uniquely varies from those without SCT, perhaps predisposing them to vascular injury, neurallymediated cold pain,⁵ or diuresis-induced hypercoagulation.

Authors’ Affiliation

Thermal Mountain Medicine Division, United States Army Research Institute of Environmental Medicine, Natick, MA

Disclaimer

The views, opinions, and findings contained in this article are those of the authors and should not be construed as an official United States Department of the Army position, or decision, unless so designated by other official documentation. This article is approved for public release, and distribution is unlimited.

References

1. Armed Forces Health Surveillance Branch. Update: cold weather injuries, active and reserve component, U.S. Armed Forces, July 2018–June 2023. MSMR. 2023;30(11):2-11.
2. Headquarters, Department of the Army, Training and Doctrine Command. TRADOC Regulation 350-29: Prevention of Heat and Cold Casualties. Jun. 15, 2023.
3. Naik RP, Smith-Whitley K, Hassell KL, et al. Clinical outcomes associated with sickle cell trait: a systematic review. Ann Intern Med. 2018;169(9):619-627. doi:10.7326/M18-1161
4. Ellenhorn Mj, Weiner D, U.S. Army Medical Research and Development Board. Report No. 81: Sickle Cell Trait and Frostbite. Army Medical Research Laboratory; 1952. https://apps.dtic.mil/sti/pdfs/ADB213334.pdf
5. Zappia KJ, Guo Y, Retherford D, et al. Characterization of a mouse model of sickle cell trait: parallels to human trait and a novel finding of cutaneous sensitization. Br J Haematol. 2017 Nov;179(4):657-666. doi:10.1111/bjh.14948

In Reply

We thank Dr. Seeley and Dr. Castellani for their interest and careful review of the November 2023 MSMR article “Update: Cold Weather Injuries Among the Active and Reserve Components of the U.S. Armed Forces, July 2018–June 2023.” The editorial team acknowledges the error in interpreting the addition of “sickle cell trait as a risk factor” as an explicit association with cold injuries in the June 2023 update of the TRADOC Regulation on Prevention of Heat and Cold Casualties. We appreciate Dr. Seeley and Dr. Castellani bringing this to our attention. A correction to the original report has been published.