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Anaemia status as measured by blood haemoglobin
This indicator describes the assessment of anaemia status and severity using blood haemoglobin concentrations.
Anaemia is highly prevalent globally, disproportionately affecting women of reproductive age and children. It negatively affects cognitive and motor development and work capacity, and among pregnant women iron deficiency anaemia is associated with adverse reproductive outcomes, including preterm delivery, low-birth-weight infants, and decreased iron stores for the baby, which may lead to impaired development (1). Iron deficiency is considered the most common cause of anaemia, but there are other nutritional and non-nutritional causes. Blood haemoglobin concentrations are affected by many factors, including altitude (metres above sea level), smoking, trimester of pregnancy, age and sex. Anaemia can be assessed by measuring blood haemoglobin, and when used in combination with other indicators of iron status, blood haemoglobin provides information about the severity of iron deficiency (2, 3). The anaemia prevalence for the population is used to classify the public health significance of the problem.
The anaemia status of the target population, as measured by blood haemoglobin concentration
Blood haemoglobin concentrations can be presented as the average concentration in the population or by using cut-off values to determine the percentage of the population with mild, moderate or severe anaemia.
Average blood haemoglobin concentration
Numerator: the sum of haemoglobin concentrations for each individual assessed
Denominator: the number of persons assessed
• Divide the numerator by the denominator to obtain the average.
Blood haemoglobin concentration below the age-, sex-, condition-, and severity-specific cut-off value for anaemia after individual adjustment for altitude and smoking, as warranted
Numerator: the number of individuals classified as having anaemia
Denominator: the number of persons assessed
• Divide the numerator by the denominator. Multiply the result by 100 to convert the number into a percentage.
Considerations for the calculations:
• Individual blood haemoglobin cut-off values to diagnose anaemia at sea level are age, sex, condition and severity specific (2).
• Individual blood haemoglobin concentrations may need to be adjusted if they are collected above sea level, or if the participant smokes cigarettes (2).
• The cut-off values, with adjustments for altitude and smoking are detailed in reference (2).
anaemia, assessment, haemoglobin, nutritional status
All
Outcome
Improved nutritional status
School age children, 12-23 months, 24-35 months, 36-47 months, 48-59 months, 6-11 months, Adolescents, All, Men, Other (not any of the above, post-menopausal women, elderly), Women of reproductive age
None,
Folate, Iron, Niacin, Vitamin A, Thiamine (vitamin B1), Vitamin B12, Riboflavin (vitamin B2), Vitamin B6, Vitamin C, Vitamin D, Vitamin E, Vitamin K, Zinc
All
Changes in blood haemoglobin concentration can be caused by factors other than the provision of additional micronutrients through an intervention.
There is good global capacity to measure blood haemoglobin concentrations, in both clinical laboratory settings and field surveys. The cost per test is relatively low.
As a biological indicator, training and expertise is needed to measure blood haemoglobin validly in surveys.
Multiple micronutrients can affect blood haemoglobin levels (such as iron, vitamin A, folate and vitamin B12); if two or more of these nutrients are provided in an intervention, it is only possible to attribute improvement to a nutrient if that nutrient is also measured in individuals.
Anaemia has many non-nutritional causes (such as menstruation, helminths, infectious diseases and haemoglobinopathies); thus, measuring blood haemoglobin is not adequate for assessing its cause (3, 4).
Measurement of blood haemoglobin concentration alone cannot assess iron deficiency.
Blood haemoglobin concentration was measured in 8236 children aged 6–59 months, during a population-based household survey in one country. Altitude data were also collected at each household, using a portable global positioning system unit. Approximately half of the children resided at 1000 m or more above sea level. During the analysis phase, the individual values for blood haemoglobin concentration for children living at 1000 m or more above sea level were adjusted for altitude.
To illustrate the altitude adjustment:
One 20-month old child lived at 1500 m above sea level. Initial blood haemoglobin value: 113 g/L
Adjustment for living at 1500 m above sea level: –5 g/L
Final altitude-adjusted value for blood haemoglobin concentration: 113 g/L – 5 g/L = 108 g/L
The anaemia cut-off value for children aged 6–59 months is 110 g/L, so, after adjusting for altitude, this child is categorized as having anaemia.
During the analysis phase, all of the individual blood haemoglobin values collected at altitudes above 1000 m were adjusted for the effects of altitude. The adjusted data were then used to calculate the percentage of children aged 6–59 months with any anaemia, and for severe anaemia.
Any anaemia
Numerator for any anaemia (altitude-adjusted haemoglobin lower than 100 g/L): 2711
Denominator: 8236
Calculation for severe anaemia (altitude-adjusted haemoglobin lower than110 g/L): 106 8,236 * 100 = 1.3%
Calculation for any anaemia (altitude-adjusted haemoglobin lower than110 g/L): 2,711 / 8,236 * 100 = 33%
Calculation for any anaemia (altitude-adjusted haemoglobin lower than 110 g/L): 2711/8236 * 100 = 33% of children had any anaemia.
Severe anaemia
Numerator for severe anaemia (altitude-adjusted haemoglobin lower than 70 g/L): 106
Denominator: 8236
Calculation for severe anaemia (altitude-adjusted haemoglobin lower than 110 g/L): 106 8 236 * 100 = 1.3% of children had severe anaemia.
1. Allen LH. Anemia and iron deficiency: effects on pregnancy outcome. Am J Clin Nutr. 2000;71(5 Suppl): 1280S-4S.
2. Haemoglobin concentrations for the diagnosis of anaemia and assessment of severity. Vitamin and Mineral Nutrition Information System. Geneva: World Health Organization; 2011 (WHO/NMH/NHD/MNM/11.1; http://apps.who.int/iris/bitstream/10665/85839/3/WHO_NMH_NHD_MNM_11.1_eng.pdf?ua=1 , accessed 04 August 2015).
3. Iron deficiency anaemia: assessment, prevention and control. A guide for programme managers. Geneva: World Health Organization; 2001 (WHO/NHD/01.3; http://apps.who.int/iris/bitstream/10665/66914/1/WHO_NHD_01.3.pdf?ua=1, accessed 6 October 2015).ICEF, UNU. Iron deficiency anaemia: assessment, prevention and control, a guide for programme managers. Geneva: World Health
4. WHO, CDC. Assessing the iron status of populations: report of a joint World Health Organization/Centers for Disease Control and Prevention Technical Consultation on the Assessment of Iron Status at the Population Level, 2nd edition. Geneva: World Health Organization; 2007 (http://apps.who.int/iris/bitstream/10665/75368/1/9789241596107_eng.pdf?ua=1, accessed 6 October 2015).