Comparison of Hemoglobin Concentration Adjusted for Altitude and Serum Iron and Ferritin to Diagnose Anemia in Childhood in Highlands

Introduction: Iron deficiency anemia in childhood is a public health problem, especially in developing countries, being one of the most prevalent nutritional disorders in Ecuador. The proper diagnosis of anemia at school age is a priority, because it is related to inadequate growth and cognitive development, low immunity and increased morbidity and mortality.

In highlands, the anemia diagnosis is difficult due to hyperbaric hypoxia stimulates erythropoiesis and the low sensitivity of conventional methods. It was established that hemoglobin concentration increases with altitude, proposing that these values must be adjusted for the altitude of residence. Thus, different models were generated to correct hemoglobin. However, other authors have an opposite position, stating that the adjustment is not required. It should be noted that, unlike hemoglobin, the content of body ferritin is not affected by the elevation above sea level, therefore constitutes an alternative for the assessment of anemia in highlands.

Hence, our objective was to evaluate different hematological parameters, including the hemoglobin correction, to diagnose anemia in children living in regions of high geographical altitude, in Ecuador.

Methods: This study has been carried out in San Juan and Yaruquíes schools, located at 3240 and 2764 meters above sea level, respectively. It was included 140 preschool and school children, who participated in the EVANES study, aged 3 to 13 years old. The 60% were female. Serum iron and ferritin and hemoglobin and hematocrit concentrations were measured in blood. The hemoglobin was evaluated considering the uncorrected values and the concentration adjusted for the geographical altitude of each region, according to World Health Organization (WHO), Center for Disease Control (CDC; for children), Dirren (for children) and Cohen (for pregnant women) methods. Children with hemoglobin levels lower than 11.5 g/dl were considered anemic (n=18/16/18/12; WHO, CDC, Dirren et al and Cohen et al, respectively).

This study was conducted in accordance to the ethical rules of the Helsinki Declaration and the current Ecuadorian law, which regulates clinical research on humans, and was approved by the Ethic Committee of the San Francisco de Quito University. Written informed consent was obtained from all schoolchildren parents or tutors.

Results: The means of age, hematocrit, unadjusted hemoglobin, serum iron and ferritin were: 8.65 ± 2.16 years, 43.01 ± 2.66 %, 14.27 ± 0.90 g/dl, 14.28 ± 4.04 µmol/l and 30.95 ± 14.33 ng/ml, respectively. When the correction factors and equations were applied, the hemoglobin concentrations were 12.45 ± 0.88 g/dl (WHO), 12.54 ± 0.88 g/dl (CDC), 12.43 ± 0.88 g/dl (Dirren) and 12.73 ± 0.89 g/dl (Cohen). No differences between female and male were found in hematological parameters.

According to unadjusted hemoglobin, no cases of anemia were determined. By applying the corrections, 13.5% (WHO), 12.0% (CDC), 13.5% (Dirren) and 9.0% (Cohen) of children were identified as anemic, and using serum ferritin and iron the percentages were 10.3% and 15.0%, respectively. When comparing the latters with the corrected hemoglobin, there were no differences in the frequency of anemia. However, of the 14 children assessed as anemic using ferritin, only 2 (0MS), 1 (CDC), 2 (Dirren) and 1 (Cohen) of them presented this condition applying the adjusted hemoglobin, and 11 to 16 non-anemic children were classified as anemic. On the other hand, taking into account adjusted hemoglobin, there were more cases of anemia among boys than girls (p<0.05), but considering the ferritin and iron, no differences were found between sexes.

In relation to the adjusted hemoglobin (all methods), the children identified as anemic presented lower hematocrit and hemoglobin (uncorrected and adjusted) levels (p<0.001) than non-anemic. No differences were found between groups in ferritin and iron concentration. Conversely, when ferritin and iron were used to divide the children, only these parameters were different in anemic and non-anemic groups (p<0.001).

Conclusions: According to our findings, the adjustment of hemoglobin concentration by geographical altitude may be an useful method to diagnose anemia in childhood at the population level but not individually. Serum ferritin is the most appropriate anemia indicator for the individual assessment in children living in highlands.