People who are not pregnant:

• Haemoglobin level:
• The World Health Organization defines anaemia as [WHO et al, 2001]:
• In men over 15 years of age: haemoglobin (Hb) below 13 g/dL.
• In non-pregnant women over 15 years of age: Hb below 12 g/dL.
• In children of 12–14 years of age: Hb below 12 g/dL.
• However, there is variability between the criteria for iron deficiency anaemia between different studies and the normal range for haemoglobin differs between different populations in the UK, so it seems reasonable to use the lower limit of the local laboratory normal range to define anaemia [British Society of Gastroenterology, 2005].
• A low haemoglobin level by itself is poorly specific for iron deficiency as anaemia can be due to other causes. In addition, in mild iron deficiency states, the haemoglobin level may be normal [AHRQ, 2006].
• Mean cell volume:
• Decreased mean cell volume (microcytosis) — the probability of iron deficiency in anaemic people increases with decreasing mean cell volume, but no specific cut-off point can be used. Microcytic anaemia is often assumed to be due to iron deficiency, but up to a third of people will have a different diagnosis (e.g. myelodysplasia, chronic inflammation) [Galloway and Smellie, 2006; Smellie et al, 2006]. Note: reference ranges may vary between laboratories.
• Other parameters of the full blood count:
• Other red blood cell changes associated with iron deficiency include [British Society of Gastroenterology, 2005; Longmore et al, 2007]:
• Reduced mean cell haemoglobin (hypochromia).
• Increased percentage of hypochromic red cells.
• Anisocytosis (variation in the size of red blood cells).
• Poikilocytosis (presence of irregular shaped red blood cells).
• A mild thrombocytosis (increase in the number of platelets) may also be suggestive of iron deficiency [British Columbia Medical Association, 2004].

Pregnant women:

• In pregnancy a physiological reduction in haemoglobin (Hb) concentration occurs, which does not represent anaemia. There is an increase in red cell mass and plasma volume; the plasma volume increases more than the red cell mass, causing a relative Hb reduction [Baker, 2000; Letsky, 2003].
• There is a lack of agreement on the Hb level for the diagnosis of anaemia during pregnancy.
• The World Health Organization (WHO) defines anaemia as an Hb level less than 11 g/dL throughout pregnancy (this is the most widely used definition worldwide) [WHO et al, 2001].
• Mean cell volume increases by approximately 4 femtolitres in pregnancy [Letsky, 2003].