Association Between Hemoglobin and Elevation Among School-Aged Children: A Verification of Proposed Adjustments

Abstract

Objectives Anemia is defined by hemoglobin (Hb) lower than normal based on cutoffs specific to age and sex. Hb increases with elevation as a response to lower blood oxygen, thus adjusting Hb for elevation is necessary before applying cutoffs. Recent evidence among preschool-aged children (PSC) and reproductive-aged women (WRA) suggests current World Health Organization (WHO) recommended Hb elevation adjustments need updating. We examined the Hb and elevation association among school-age children (SAC) to confirm these findings. Methods Biomarkers Reflecting Inflammation and Nutritional Determinants of Anemia (BRINDA) project data include SAC aged 5–14 years (n = 23,454; 53.5% female) with data on Hb and elevation (−6 to 3,834 meters, m) from 6 population-based surveys from 5 countries (Columbia, Ecuador, Malawi, Mexico, United Kingdom). Anemia was defined as Hb < 115 g/L for SAC < 12 years and < 120 g/L for SAC 12–14 years after elevation adjustments. Generalized linear models were used to assess the association between Hb and elevation, including controlling for inflammation-corrected iron and vitamin A deficiency. Hb adjustments for each 500 m increase in elevation from sea level are proposed and compared to current WHO recommendations and new proposed PSC and WRA adjustments. Results Hb was positively associated with elevation. There was no sex interaction, and the association was robust to model specification. The association among SAC and the resulting Hb adjustments were consistent with PSC and WRA findings, suggesting current WHO recommendations may under-adjust Hb at lower elevation (500–2500 m) and over-adjust Hb at higher elevation (>3000 m). Anemia prevalence in SAC using new elevation adjustments increased by 0.7 (UK) to 14.1 (Malawi) percentage points relative to current WHO elevation adjustments. Conclusions Results confirm current WHO recommended Hb elevation adjustments may need updating, and anemia prevalence in SAC may be higher than currently estimated. Findings will inform global guidelines on use of elevation-adjusted Hb for anemia assessment and possible need for intervention among SAC. Funding Sources Bill & Melinda Gates Foundation, Centers for Disease Control and Prevention, Eunice Kennedy Shriver National Institute of Child Health and Human Development, HarvestPlus, and United States Agency for International Development.

New WHO guideline on the definition of anemia: implications for 6-35 months old children in Peru 2009-2023

“…In children <60 months old (11) some between country heterogeneity is shown. The equation in the 2024 guideline is nearly identical to the school age fit (10).…”

“…This better reflects the physiology than the abrupt transition in the guideline, which generates an artificial jump at 24 months of age. • Two papers on altitude for children <60 months old and women 15-49 years old (11) and school age children (10). Their relevant data sources (1999-2019, BRINDA project) are surveys (Mexico, Colombia, Ecuador, Afghanistan, Nepal, Laos, Malawi, Papua New Guinea, Azerbaijan, Georgia, UK and USA), a surveillance (Guatemala/SIVESNU), and two evaluations (Ghana/GIFTS and Bolivia/NIDI (El Alto)).…”

“…Children anemia is a major national and international public health problem (1-5) particularly by its consequences on early development. The World Health Organization (WHO) published last 06-Mar a new guideline (6) on the hemoglobin cutoff points which define anemia, updating a previous guideline (7,8) taking into account important and recently published evidence (9)(10)(11). The new guideline has three main changes for small children: it reduces the cutoff point for the 6-23 months old group, it modifies the altitude adjustment equation (lowering the cutoff points for altitudes above 3000m, while rising the cutoff points for altitudes below that level) and it requires venous blood measurement using auto-analyzers or calibrated portable devices, both under quality control.…”

Characteristics of hemoglobin distributions in preschool children and non-pregnant women of reproductive age and their implications for establishing quality control criteria for hemoglobin data in field surveys: evidence from 483 surveys conducted in refugee settings worldwide

“…Indeed, commonly cited values for acceptable SDs of Hb distribution (1.1-1.5 g/dL range), as determined by the HemoCue system in cross sectional surveys, are based on the authors' empirical experience (with no supporting data presented) [12]. Multiple ranges for minimum and maximum plausible Hb values for nonpregnant women and children have been described and used in recent literature without further justification, for example, 2.0 g/dL to 30.0 g/dL [7], 2.5 g/dL to 20.0 g/dL [1], 4.0 to 18.0 g/dL [12], and 4.0 g/dL to 21.0 g/dL [13].…”

Niveles de hemoglobina para la determinación de la anemia: nueva guía de la Organización Mundial de la Salud y adecuación de la norma nacional

“…Varios investigadores han cuestionado la necesidad de ajustar la hemoglobina por la altura, por lo menos en tres continentes (América, África y Asia) (6)(7)(8) . En tanto otros investigadores sugieren rehacer la fórmula de ajuste en base a los nuevos datos colectados a través del mundo (9) . Un estudio reciente realizado en Perú propone que la formula CDC/OMS subestima la anemia en niños de 6 a 8 meses que residen en ciudades entre los 1400 y 2600 msnm, mientras que podría sobreestimar la anemia entre los 3000 y 4300 msnm (10) .…”