Iron is an essential mineral for transporting oxygen around the body. Iron deficiency can lead to fatigue, tiredness, anaemia and decreased immunity. There are several tests that can be used in combination to determine the iron status of the population, including Iron Deficiency Anaemia (IDA).
There are three stages that occur during the development of IDA, which can be assessed by measuring serum ferritin and soluble transferrin receptor (sTfR) and haemoglobin (Hb). At the first stage, when iron stores in the body decrease, there is also a decrease in serum ferritin levels, however this can be affected by the presence of inflammation or infection. During the second stage, where iron stores are depleted and exhausted, levels of sTfR increase and the production of Hb ceases, however Hb levels can be within normal ranges. In the final stage Hb levels decrease indicating the presence of anaemia or IDA.1
In the National Aboriginal and Torres Strait Islander Health Measures Survey (NATSIHMS), the biomarkers that were used to measure the amount of iron stored in the body included serum ferritin and sTfR. C-reactive Protein (CRP) levels were measured purely as an interpretation aid (detects presence of inflammation) for determining ferritin levels. The haemoglobin biomarker is used to measure the presence of anaemia, which can occur with or without iron deficiency.
Ferritin is a biomarker that indicates the level of iron stored in the body. It is important to detect any depleted stores of iron in the body as iron depletion is present prior to the onset of anaemia.1 Levels of ferritin can be affected by infection or inflammation,2 therefore people with inflammation (defined in the NATSIHMS as a C-reactive protein level of >10 mg/L) were excluded from the NATSIHMS ferritin results.
Soluble Transferrin Receptor (sTfR)
Soluble Transferrin Receptor (sTfR) is another measure of iron levels in the body. It is not as affected by infection or inflammation to the extent of other measures, such as ferritin. When ferritin results indicate depleted iron stores, sTfR can be used to assess the severity of the iron depletion.1
Haemoglobin (Hb) is a protein found in red blood cells. It contains a large amount of iron and helps transport oxygen from the lungs to the rest of the body. Anaemia is caused by a decrease in either the number of red blood cells in the body or the quantity of haemoglobin within red blood cells.1 The NATSIHMS measured the concentration of haemoglobin in the blood, which can help determine the presence of anaemia.
More information regarding the biomedical tests and cut off points can be found in the relevant subsections of this Users' Guide.
1 Gibson RS 2005, Principles of Nutritional Assessment, 2nd ed, New York: Oxford University Press.
2 Thurnham DI, McCabe GP 2012, 'Influence of infection and inflammation on biomarkers of nutritional status with an emphasis on vitamin A and iron'. In: World Health Organization. Report: Priorities in the assessment of vitamin A and iron status in populations, Panama City, Panama, 15–17 September 2010. Geneva, World Health Organization, <http://www.who.int/nutrition/publications/micronutrients/background_paper4_report_assessment_vitAandIron_status.pdf>, Last accessed 08/09/2014.