Implications of changes in WHO haemoglobin elevation adjustment guidelines on global, regional, and national anaemia...

Adjustment of haemoglobin concentrations for elevation is essential for anaemia assessments of both individuals and populations. Whereas the previous WHO anaemia definitions released in 2001 used an elevation adjustment derived from small sample sizes with limited representativeness, the 2024 WHO global anaemia definitions reflect empirical assessments across several geographies and settings derived from population-representative surveys. We aimed to assess the effect of these changes on estimates of global anaemia burden.

In this population-based modelling study, using an identical set of input data from population-based surveys, we created two datasets in parallel, where each input haemoglobin concentration was adjusted using the WHO 2001 and WHO 2024 elevation adjustment methods. We estimated mild, moderate, and severe anaemia prevalence by age and sex for 204 countries and territories from 1990 to 2023 for each dataset using spatiotemporal Gaussian process regression and ensemble distribution modelling. We then analysed the overall differences in anaemia prevalence and years lived with disability to assess the effect of the WHO 2024 elevation adjustment method on the global landscape of anaemia. Uncertainty was propagated in each step of the modelling process by sampling draws of the posterior distribution of each estimated quantity.

Global anaemia prevalence for all ages and both sexes in 2023 was estimated to be 26·4% (95% uncertainty interval [UI] 22·6-31·9) using the WHO 2024 elevation adjustment method, which was 2·4 percentage points (2·2-2·7) higher than the total anaemia prevalence estimated using the WHO 2001 method (24·0% [20·6-29·3]). This increase equates to 198 million (196-199) newly enumerated cases, increasing the rank of anaemia from the third to the second largest cause of disability globally. The largest absolute increases in anaemia prevalence were in locations between 500 m and 2000 m in elevation, which include countries in eastern sub-Saharan Africa, central Asia, central America, and South America.

Understanding the effect of anaemia requires unbiased and comparable estimates of anaemia burden. To our knowledge, we produced the first set of global estimates of anaemia burden by location, year, age, and sex using the WHO 2024 elevation adjustment method and compared them with estimates using the previous method. Policy makers should consider this modification when designing interventions to manage and prevent anaemia, particularly in regions most affected by changes in elevation adjustment.

Gates Foundation.