To the Editor. Anemia is a treatable and preventable condition that significantly affects women of childbearing age, pregnant women, and infants. Worldwide, the prevalence of anemia has slightly decreased in women aged 15 to 49 years (31% in 2010 to 30% in 2019), as well as in pregnant women (41% to 36% in the same period); low- and middle-income countries still maintain the highest prevalence rates ¹1. Stevens GA, Paciorek CJ, Flores-Urrutia MC, Borghi E, Namaste S, Wirth JP, et al. National, regional, and global estimates of anaemia by severity in women and children for 2000-19: a pooled analysis of population-representative data. Lancet Glob Health. 2022;10(5):e627-39.. These figures have led the World Health Organization (WHO) to consider anemia as a problem that needs to be controlled soon, therefore one of its established objectives is a 50% reduction in anemia in women of childbearing age by 2025 ²2. World Health Organization. Global nutrition targets 2025: anaemia policy brief. World Health Organization; 2014. Disponible en: https://iris.who.int/bitstream/handle/10665/148556/WHO_NMH_NHD_14.4_eng.pdf?sequence=1.
https://iris.who.int/bitstream/handle/10... .

Although anemia figures vary according to region, altitude, sex, age and other clinical characteristics, WHO published in 2024 a new guideline for the assessment of anemia and its severity ³3. World Health Organization. Guideline on haemoglobin cutoffs to define anaemia in individuals and populations. 2024; Disponible en: https://iris.who.int/bitstream/handle/10665/376196/9789240088542-eng.pdf?sequence=1.
https://iris.who.int/bitstream/handle/10... . One of the novelties of this guideline is the modification of the hemoglobin adjustment for altitude of residence to assess the effect of living in regions below 2500 meters above mean sea level (MASL) ³3. World Health Organization. Guideline on haemoglobin cutoffs to define anaemia in individuals and populations. 2024; Disponible en: https://iris.who.int/bitstream/handle/10665/376196/9789240088542-eng.pdf?sequence=1.
https://iris.who.int/bitstream/handle/10... . In comparison with the 1989 US Centers for Disease Control and Prevention (CDC) recommendation to adjust hemoglobin from 1000 MASL ⁴4. Centers for Disease Control (CDC). CDC criteria for anemia in children and childbearing-aged women. MMWR Morb Mortal Wkly Rep. 1989;38(22):400-4., the new WHO guideline proposes an adjustment of approximately 4 g/L for every 500 MASL ³3. World Health Organization. Guideline on haemoglobin cutoffs to define anaemia in individuals and populations. 2024; Disponible en: https://iris.who.int/bitstream/handle/10665/376196/9789240088542-eng.pdf?sequence=1.
https://iris.who.int/bitstream/handle/10... . In addition, a differentiated cut-off point for the second trimester of gestation was included in the new guideline ³3. World Health Organization. Guideline on haemoglobin cutoffs to define anaemia in individuals and populations. 2024; Disponible en: https://iris.who.int/bitstream/handle/10665/376196/9789240088542-eng.pdf?sequence=1.
https://iris.who.int/bitstream/handle/10... . Finally, on April 8, 2024, the Peruvian Ministry of Health approved NTS 213-MINSA/DGIESP-2024, which implements the new guideline in Peru ⁵5. Ministerio de Salud. Resolución Ministerial N° 251-2024/MINSA [Internet]. 2024 [citado el 10 de mayo de 2024]. Disponible en: https://busquedas.elperuano.pe/dispositivo/NL/2277624-1.
https://busquedas.elperuano.pe/dispositi... . These changes could modify the anemia figures and the prioritization of public health measures. Therefore, this study aimed to determine changes in the prevalence of anemia in Peruvian women according to the two described criteria.

For this study we used the Demographic and Family Health Survey (ENDES) 2023 and included 31,639 women aged 15-49 years. The analysis was carried out using Stata 18 (StataCorp, College Station, Texas, USA), incorporating strata, clusters and sampling weights. Descriptive measures were used to report anemia prevalences along with their 95% confidence intervals and percentage point (pp) changes. The variable of interest was the presence of anemia. Two anemia conditions were estimated based on the altitude-adjusted hemoglobin concentration of the cluster of residence, using the cutoff points established by the CDC criteria ⁴4. Centers for Disease Control (CDC). CDC criteria for anemia in children and childbearing-aged women. MMWR Morb Mortal Wkly Rep. 1989;38(22):400-4. and the new WHO criteria ³3. World Health Organization. Guideline on haemoglobin cutoffs to define anaemia in individuals and populations. 2024; Disponible en: https://iris.who.int/bitstream/handle/10665/376196/9789240088542-eng.pdf?sequence=1.
https://iris.who.int/bitstream/handle/10... . The adjustments were made according to the altitude of the cluster, applying the CDC criteria from 1000 MASL and the WHO criteria from 500 MASL, with the following equations:

WHO (g/L) =0.0056384 * A+ 0.0000003 * A²

CDC (g/L)=-0.32 * (A * 0.0033)+ 0.22 * (A * 0.003)²

Where: A=altitude in MASL

By applying the new WHO criteria, we found that the prevalence of anemia in women increased by 0.3 pp. Among pregnant women, the prevalence decreased by 4.2 pp. The prevalence of anemia increased at altitudes between 1000 and 3000 MASL by 9.0 and 5.9 pp, respectively. In contrast, a reduction of up to 18.9 pp was found at altitudes ≥4000 MASL. We found an increase of 3.8 pp in the jungle region. On the other hand, when analyzing by department, the reduction in prevalence in Puno was noteworthy, as it was no longer the department with the highest prevalence of anemia, with a decrease of 12.5 pp (31.8% with CDC vs. 19.3% with WHO). Other changes in different departments are shown in Table 1.

Our results show that the implementation of the new WHO guidelines will lead to a change in the prevalence of anemia in pregnant women and women living at different altitudes. It is noteworthy that the prevalence of anemia increased at altitudes below 3000 MASL, while it decreased from 3000 MASL onwards. This finding is reaffirmed by the fact that Puno, one of the departments with the highest altitude, went from being the department with the highest prevalence to presenting figures that are even lower than those of Lima, leaving Loreto as the department with the highest prevalence (29.2% with WHO criteria). These findings are explained by the difference between CDC and WHO for hemoglobin adjustments. While at altitudes >3194.2 MASL the WHO 2024 guidelines make a lower adjustment compared to CDC, at altitudes <3194.2 MASL WHO recommends a higher adjustment ³3. World Health Organization. Guideline on haemoglobin cutoffs to define anaemia in individuals and populations. 2024; Disponible en: https://iris.who.int/bitstream/handle/10665/376196/9789240088542-eng.pdf?sequence=1.
https://iris.who.int/bitstream/handle/10... (see Figure in Supplementary Material). In addition, the latter is more pronounced between 1000 and 2500 MASL. This explains the increase in prevalence in departments with populations residing in this altitude range, such as San Martín and Amazonas. All of the above suggests that the effect of altitude may have been overestimated to date, which could have implications for the allocation of resources to address the public health burden generated by anemia.

In conclusion, the implementation of the new WHO criteria significantly changes the prevalence of anemia in Peruvian women, especially at altitudes above 3000 MASL and in departments at high altitude. This indicates that previous estimates may have overestimated hemoglobin levels in Peruvian women. Finally, our results underscore the need to accurately determine normative hemoglobin values in our population using markers such as serum ferritin. Likewise, it will be necessary to rethink public health strategies and the allocation of resources to more accurately address the burden of anemia in the country and “leave no one behind”.

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