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Iron status as measured by serum or plasma ferritin
This indicator estimates iron status in an individual, using serum or plasma ferritin.
Ferritin is a sensitive measure and one of the most efficient indicators of iron deficiency, since it measures iron stores. Iron deficiency is the world’s most prevalent micronutrient deficiency, with profound consequences for human health and development. Women of reproductive age are one of the most vulnerable populations for iron deficiency, which has negative consequences for the physical capacity and cognitive performance of female adolescents and adults. Women who consume foods made with flour that is fortified with iron may improve their iron status, increase iron stores for pregnancy and avoid the negative consequences of iron deficiency (1, 2). The World Health Organization (WHO) and the United States Centers for Disease Control and prevention (CDC) recommend ferritin as a response indicator to evaluate the impact of an intervention aiming to control iron deficiency in populations (3). It may also be important to monitor other categories of status, including normal iron stores and severe risk of iron overload.
The iron status of the target population, as measured by ferritin concentration
Iron status can be presented as the average ferritin concentration in the population, or by using cut-off values to determine the percentage of the population with depleted iron stores, normal iron stores or severe risk of iron overload.
Average ferritin concentration
Numerator: the sum of ferritin concentrations for each individual assessed
Denominator: the number of persons assessed
• Divide the numerator by the denominator to obtain the average.
Percentage of the population with depleted iron stores, normal iron stores or severe risk of iron overload
Numerator: the number of individuals with depleted iron stores, normal iron stores or severe risk of iron overload
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:
• There are established ferritin cut-off values for depleted, normal and severe risk of iron overload, based on ferritin iron stores by age, and for sex for those aged 5 years and older (1). Ferritin concentrations decline during late pregnancy, regardless of iron stores, which limits the usefulness of this indicator during pregnancy. There are no WHO ferritin cut-off values for pregnant women.
• Ferritin can also be used to classify those with iron deficiency anaemia, by coupling ferritin data with haemoglobin levels (or other marker of anaemia). When using haemoglobin data, they should be adjusted for smoking and altitude (1).
• Ferritin is increased among those experiencing inflammation or infection, which can result in an underestimation of the prevalence of iron deficiency in a population. The ferritin data can be interpreted in conjunction with indicators of inflammation and infection, to better understand this influence, as well as to potentially adjust or exclude the ferritin data for those with inflammation and infection. There is no agreed-upon method to address the influence of inflammation and infection on ferritin values in population-based assessments. For survey reports, it may be useful to report the ferritin data for the entire population in the body of the text, and then in the appendix to report the data taking into consideration the effect of inflammation and infection.
• The cut-off value for ferritin to assess depleted iron stores is 12 µg/L in children aged under 5 years, and 15 µg/L for children aged over 5 years, men and non-pregnant women. Values above 200 µg/L in adult men and above 150 µg/L in adult women indicate a severe risk of iron overload. For haemoglobin, the corresponding values are 110 g/L for children under 5 years, 115 g/L for children aged 5–11 years, 120 g/L for children aged 12–14 years and non-pregnant women up to 49 years. For men over 15 years, the value is 130 g/L (1). The values for haemoglobin need to be adjusted for altitude and smoking. At sea level, no adjustment is required but at increasing altitude a subtraction is needed, ranging from –2 g/L at 1000 m to –45 g/L at 4500 m. For smokers, the adjustment ranges from –0.3 g/L for those who smoke half to one pack a day, to –0.7 for 2 or more packs per day.
anaemia, assessment, ferritin, iron deficiency, iron overload, iron status, nutritional status, plasma, serum
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, Women of reproductive age
None,
Iron
Community, Health systems, Market-based
Changes in iron status can be caused by factors other than the provision of additional iron through an intervention.
This is an indicator to measure the impact of programmes that deliver iron, and is recommended by WHO and CDC (3). Anaemia is associated with many non-nutritional causes, and measuring only haemoglobin is not adequate for assessing iron deficiency.
The use of ferritin to assess iron status works well in populations where the prevalence of infectious and inflammatory disorders is low.
Significant expertise and resources are required to validly collect, analyse and interpret the data used to calculate this indicator.
Other factors beyond poor dietary intake of iron can cause iron deficiency (such as menstruation, malaria, soil-transmitted helminth, and other infections) and iron overload (such as haemochromatosis).
There is no agreed-upon solution for addressing the influence of inflammation and infection on ferritin values. This may reduce the ability to compare results among different surveys. Ferritin is an acute-phase protein. Values may not reflect iron status accurately in the presence of infection. The utility of ferritin assays is therefore more limited in low- and middle-income countries where malaria, HIV, tuberculosis and other infectious and inflammatory disorders are prevalent.
The value of ferritin assays may not be appropriate for certain groups in stages of the life-cycle during which depleted iron stores are physiologically appropriate (second and third trimesters of pregnancy) (1).
A project on large-scale fortification of wheat flour was implemented in a country. To determine the potential effectiveness of the flour fortification in improving iron status, data were collected in a sentinel population where the families were expected to have early access to fortified wheat flour. Within this area, women of reproductive age from 40 families were sampled. Serum ferritin was measured in women during year one and 3 years later. In the third round, significant increases were observed in the average serum ferritin concentration, as well as a decrease in the prevalence of iron deficiency.
Example of a calculation for assessing the prevalence of depleted iron stores using serum ferritin:
Year one:
Numerator for depleted iron stores (serum ferritin <15 µg/L): 18
Denominator: 40
Calculation: 18/40 * 100 = 45.0% of women sampled had depleted iron stores.
Year three:
Numerator for depleted iron stores (serum ferritin <15 µg/L): 10
Denominator: 40
Calculation: 10/40 * 100 = 25.0% of women sampled had depleted iron stores.
1. Serum ferritin concentrations for the assessment of iron status and iron deficiency in populations. Vitamin and Mineral Nutrition Information System. Geneva: World Health Organization; 2011 (WHO/NMH/NHD/MNM/11.2; http://www.who.int/vmnis/indicators/serum_ferritin.pdf, accessed 6 October 2015).
2. WHO, United Nations Children’s Fund (UNICEF), United Nations University (UNU). Iron deficiency anaemia: assessment, prevention, and control. A guide for programme managers. Geneva: World Health Organization; 2001 (WHO/NHD/01.3; (http://www.who.int/nutrition/publications/en/ida_assessment_prevention_control.pdf, accessed 6 October 2015).
3. WHO, CDC. Assessing the iron status of populations: including literature reviews: 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).