Association between Hemoglobin and Elevation among School-aged Children: A Verification of Proposed Adjustments

Anemia is defined by a hemoglobin (Hb) concentration lower than normal based on cutoffs specific to age, sex, and pregnancy status. Hb increases with elevation as an adaptive response to lower blood oxygen saturation, thus, adjusting Hb concentrations for elevation is necessary before applying cutoffs.

Recent evidence among preschool-aged children (PSC) and nonpregnant reproductive-aged women (WRA) suggests that current World Health Organization (WHO)-recommended Hb adjustments for elevation need updating. To confirm these findings, we examined the cross-sectional association between Hb and elevation among school-aged children (SAC).

Using data from 9 population-based surveys, we examined 26,518 SAC aged 5-14 y (54.5% female) with data on Hb and elevation (-6 to 3834 m). We used generalized linear models to assess the association between Hb and elevation under varying conditions, including controlling for inflammation-corrected iron and vitamin A deficiency (VAD). Hb adjustments for each 500-m increase in elevation were estimated for SAC and compared with existing adjustments and those estimated for PSC and WRA. We evaluated the impact of these adjustments on anemia prevalence.

Hb concentration (g/L) was positively associated with elevation (m). The SAC-elevation adjustments were consistent with those reported among PSC and WRA and suggest current recommendations may under-adjust Hb for those residing at lower elevations (<3000 m) and over-adjust Hb for those residing at higher elevations (>3000 m). Among the surveys included, the proposed elevation adjustments increased anemia prevalence among SAC by 0% (Ghana and United Kingdom) to 15% (Malawi) relative to current elevation adjustments.

Results confirm that current recommended Hb adjustments for elevation may need updating, and anemia prevalence among SAC may be higher than currently estimated. Findings will inform the WHO's reexamination of global guidelines on the use of Hb adjustments for anemia assessment and may result in improved identification and treatment of anemia.