Anemia

Anaemia is usually defined by a low haemoglobin concentration adjusted for altitude, and (among adults) adjusted for smoking. One of the most common causes of anaemia is iron deficiency. However, anaemia cannot necessarily be used as a proxy for iron deficiency because anaemia can result from many other factors, including:
  • Malaria and other infections
  • Other causes of blood loss (such as heavy menses, haemorrhage in childbirth, trauma, gastrointestinal bleeding due to ulcers)
  • Deficits in other nutrients (for example vitamin A, folic acid, vitamin B12)
  • Haemoglobinopathies (such as sickle cell or thalassemia)
  • Overweight, obesity and other causes of chronic inflammation (for example chronic kidney disease) 1
  • Blood loss due to infection (from such conditions as hookworm, schistosomiasis or H. pylori) 2, 3.

Haemoglobin:

Haemoglobin level is an indicator of anaemia, a condition in which the number of red blood cells or their oxygen-carrying capacity is insufficient to meet physiologic needs. Iron deficiency is one of the most common causes of anaemia globally, although anaemia can also be caused by other conditions 4.
Additional haematologic indicators of anaemia include haematocrit, mean cell volume and red blood cell distribution width. It is recommended that haemoglobin be used for assessing anaemia in cross-sectional surveys. For assessing the prevalence of iron deficiency anaemia, it is recommended that countries collect data on haemoglobin and at least one biochemical test for iron deficiency, along with measures of inflammation as appropriate 5.

Specimen collection and management: Haemoglobin is typically measured in fresh whole blood samples in the field 6. For non-field-based analysis, haemoglobin is most commonly measured in EDTA blood samples. In this case, the samples should be refrigerated as soon as possible and need to be analysed within 1–2 days of collection.

In the case of field analysis, capillary drops, pooled capillary blood into small blood collection tubes, or venous blood can be used. Capillary blood from a finger prick is collected by capillary action in a cuvette, which is then placed in the photometer that displays the haemoglobin concentration within one minute. The accuracy of haemoglobin measurement may be improved by pooled capillary or venous blood. For pooled capillary blood, collect 250–500 μL in a small blood collection tube containing an anticoagulant such as EDTA or heparin, gently mixing the blood by inverting the tube several times to prevent clotting, and then filling the cuvette with blood from the blood collection tube 7, 8. For venous blood, collect 3-5 mL in a vacuum blood collection tube containing an anticoagulant such as EDTA or heparin, gently mixing the blood by inverting the tube several times, and then filling the cuvette with blood from the collection tube for analysis 6, 8. A comparison of nationally representative surveys measuring haemoglobin using HemoCue® with capillary (DHS) or venous (BRINDA) samples, showed substantial differences in anaemia prevalence estimates, which were consistently lower in venous compared to capillary 9.

The procedures for specimen collection and analysis using a haemoglobinometer must be standardized. This requires careful training of survey technicians. It is particularly important not to squeeze the finger too hard when collecting capillary blood because this can cause interstitial fluid to mix with the blood and result in an incorrect haemoglobin concentration. Poor quality collection of capillary blood can in turn lead to low or high haemoglobin concentrations for population-based surveys 6.

Biomarker analysis: The most commonly used method for field-based measurement of haemoglobin in population surveys is photometric determination using a portable haemoglobinometer 6, 9. The procedure does not require specialized laboratory personnel and the haemoglobinometer may be operated on four AA batteries, which makes it particularly useful in the field. Manuals and tutorial videos for haemoglobinometers are available online, making it easier to follow proper operation 7, 8. The HemoCue® haemoglobinometer has been validated against traditional haemoglobin laboratory methods and found to have adequate accuracy and precision in controlled settings 7, 8. The accepted reference method for haemoglobin measurement is the cyanmethaemoglobin method 10.

A systematic review commissioned by WHO for reviewing haemoglobin cutoffs as part of the project to review cutoffs to diagnose anaemia concluded that capillary fingerprick blood usually produces higher haemoglobin concentrations compared with venous blood, that individual drops produced lower concentrations than pooled capillary blood and that compared to automated haematology analysers, other methods (cyanmethaemoglobin, WHO Colour Scale, paper‐based devices, HemoCue® Hb‐201 and Hb‐301, and Masimo Pronto®) overestimated haemoglobin concentrations 6.

Approximate budget requirements for analysis: Each haemoglobinometer costs approximately US$ 300–500 depending on the model, and the cuvette cost is approximately US$ 0.50 when both items are procured through UNICEF. While most of the field experience in the use of portable haemoglobinometers has been with HemoCue®, other portable haemoglobinometers are available from other manufacturers at a similar cost (US$ 400–600).

Adjustments and interpretation of results: WHO has established cutoff values for haemoglobin to define anaemia by population group, including for pregnant women 5, 11. These are shown in Tables 3.23.4. Table 3.2 presents haemoglobin levels used to diagnose anaemia, while Table 3.3 defines the public health significance of anaemia in a population. Table 3.4 shows the adjustments of haemoglobin values that are required to correct for changes that occur due to altitude and smoking (based on the average number of cigarettes per day). Populations living at high altitudes where oxygen pressure is low have higher haemoglobin concentrations, reduced oxygen saturation and an increased production of red blood cells to ensure oxygen supply to tissues. These physiological characteristics would result in identifying fewer cases of anaemia using the cutoff values in Table 3.2. The approach shown in Table 3.4 adjusts everyone’s haemoglobin value first, then applies the haemoglobin cutoff value for anaemia from Table 3.2.

The distribution of haemoglobin among sub-groups of the population can also provide important information concerning the aetiology of anaemia (vitamin A deficiency, iron deficiency, other nutrient deficiencies, inflammation status or blood disorders) 12. For example, if the iron deficient population has the same distribution of haemoglobin as the iron replete population, then iron deficiency is unlikely to be the cause of anaemia. On the other hand, if the iron deficient population has a lower haemoglobin distribution, then it is more likely that iron is a cause of anaemia in that population.

Understanding the aetiology of anaemia is important for the design and evaluation of anaemia prevention strategies and programmes, thus a micronutrient survey should assess some of the factors in the above list. For example, in all malaria endemic countries, malaria should be assessed. Rapid diagnostic tests cost very little (around US$ 1) and are easy to ad#minister. Many resources that explain the samples and analyses required for assessing malaria and other infections, such as helminths, are available from WHO 13,14,15.

Table 3.2. Haemoglobin cutoff values to define anaemia in individuals for people living at sea level (g/L) a

Anaemiab
Population Non-anaemiab
Mild
Moderate
Severe
Children 6-59 months
≥110
100-109
70-99
<70
Children 5-11 years
≥115
110-114
80-109
<80
Children 12-14 years
≥120
110-119
80-109
<80
Non-pregnant women (15 years and older)
≥120
110-119
80-109
<80
Pregnant women
≥110
100-109
70-99
<70
Men (15 years and older)
≥130
110-129
80-109
<80

aSource: reference 11
bHaemoglobin in grams per litre.

Table 3.3. Classification of public health significance of anaemia at the population level based on estimated prevalence of low haemoglobinaa

Category of public health significance
Prevalence of anaemia (%)
Severe
≥40
Moderate
20.0-39.9
Mild
5.0-19.9
Normal
≤4.9%

aSource: reference11.

Table 3.4. Haemoglobin adjustment for altitude and cigarette smokingaa

Altitude
(metres above sea level)
Adjustment to individual
haemoglobin value (g/L)
<1000 No adjustment
1000-1499
-2
1500-1999
-5
>2000-2499
-8
2500-2999
-13
3000-3499
-19
3500-3999
-27
4000-4499
-35
>4500
-45
Cigarettes smoked per day
Non-smoker
0
Smoker (All)
-3
1/2-1 packet per day
-3
1-2 packets/day
-5
>2 packets/day
-7

aSource: reference11.

  1. Cook JD, Skikne BS, Baynes RD. Iron deficiency: the global perspective. Adv Exp Med Biol. 1994;356:219–28. 

  2. Olds GR. Deworming the world. Trans Am Clin Climatol Assoc. 2013; 124:265–74. 

  3. Ražuka-Ebela D, Giupponi B, Franceschi F. Helicobacter pylori and extragastric diseases. Helicobacter. 2018;23 Suppl 1:e12520. doi: 10.1111/hel.12520. 

  4. Whitehead RD, Zhang M, Sternberg MR, Schleicher RL, Drammeh B, Mapango C et al. Effects of preanalytical factors on hemoglobin measurement: A comparison of two HemoCue® point-of-care analyzers. Clin Biochem. 2017; 50:513–20. doi: 10.1016/j.clinbiochem.2017.04.006. 

  5. Nutritional anaemias: tools for effective prevention and control. Geneva: World Health Organization; 2017. Licence: CC BY-NC-SA 3.0 IGO (https://www.who.int/publications/i/item/9789241513067, accessed 13 June 2020).  2

  6. Whitehead RD Jr, Mei Z, Mapango C, Jefferds MED. Methods and analyzers for hemoglobin measurement in clinical laboratories and field settings. Ann N Y Acad Sci. 2019;1450:147–71. doi:10.1111/nyas.14124.  2 3 4 5

  7. HemoCue® Hb 301 System. Ängelholm: HemoCue AB; 2015 (https://www.hemocue.com/-/media/hemocue-images/hemocuedotcom-images/product-images/hb/pdf-folders-etc/web-update-01092015.pdf, accessed 13 June 2020).  2 3

  8. HemoCue® Hb 201 DM System. Ängelholm: HemoCue AB; 2014 ([https://www.hemocue.com/-/media/hemocue-images/hemocuedotcom-images/product-images/hb/pdf-folders-etc/hb-201-dm-system.pdf (https://www.hemocue.com/-/media/hemocue-images/hemocuedotcom-images/product-images/hb/pdf-folders-etc/hb-201-dm-system.pdf)], accessed 13 June 2020).  2 3 4

  9. Hruschka DJ, Williams AM, Mei Z, Leidman E, Suchdev PS, Young MF et al. Comparing hemoglobin distributions between population-based surveys matched by country and time. BMC Public Health. 2020;20:422. https://doi.org/10.1186/s12889-020-08537-4 2

  10. Bansal PG, Toteja GS, Bhatia N, Gupta S, Kaur M, Adhikari T et al. Comparison of haemoglobin estimates using direct & indirect cyanmethaemoglobin methods. Indian J Med Res. 2016; 144:566–71. doi: 10.4103/0971-5916.200882. 

  11. Haemoglobin concentrations for the diagnosis of anemia and assessment of severity. Geneva: World Health Organization; 2011 (WHO/NMH/NHD/MNM/11.1; https://apps.who.int/iris/bitstream/handle/10665/85839/WHO_NMH_NHD_MNM_11.1_eng.pdf, accessed 13 June 2020). 

  12. Pasricha SR, Drakesmith H. Iron deficiency anemia: problems in diagnosis and prevention at the population level. Hematol Oncol Clin North Am. 2016;30:309–25. doi: 10.1016/j.hoc.2015.11.003. 

  13. Assessing the epidemiology of soil-transmitted helminths during a transmission assessment survey in the global programme for the elimination of lymphatic filariasis. Geneva: World Health Organization; 2015 (WHO/HTM/NTD/PCT/2015.2; https://apps.who.int/iris/bitstream/handle/10665/153240/9789241508384_eng.pdf, accessed 13 June 2020). 

  14. Malaria microscopy quality assurance manual – version 2. Geneva: World Health Organization; 2016 (https://apps.who.int/iris/bitstream/handle/10665/204266/9789241549394_eng.pdf, accessed 13 June 2020). 

  15. Malaria indicator survey toolkit [online toolkit]. Rockville: ICF; 2018 (https://malariasurveys.org/toolkit.cfm, accessed 13 June 2020). 

Best practices for haemoglobin measurement in population-level anaemia surveys - Technical brief

This brief describes the current best practices for haemoglobin measurement. It provides guidance for people who are planning or implementing field surveys that will assess anaemia prevalence at a population level. Published by WHO, 2024.

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Instructions for estimating anaemia prevalence_2024

This document provides instruction for how to prepare and clean raw hemoglobin data as well as how to estimate anemia prevalence in a population.

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