ADULT IRON DEFICIENCY:
  NOT ALWAYS ANAEMIA

 NOTE and DISCLAIMER:

These articles are for general interest of qualified family physicians only. They are NOT for diagnostic or therapeutic use.

The articles are definitely NOT for any public use whatever, nor intended in any way to be taken as advice for any medical or health condition.

Serum ferritin is the best indicator of iron deficiency

Iron deficiency is a common problem in adult women - around 8% of reproductive aged females have biochemical evidence of the condition (for more detailed statistics in the Australian context, see table. With the successful campaign run by the meat industry in recent years, many family physician' have experienced their female patients asking for a blood test to check their own iron status. What approach should the family physician take?

The first thing to realise is that much iron deficiency is asymptomatic, and anaemia only occurs in a relatively small proportion of cases. Whilst this might makes it a less urgent clinical problem, it does not mean that iron deficiency is not important to treat. There are negative outcomes in pregnancy (both for mother and baby) and increasing evidence of adverse effects on work and sports performance, concentration and perhaps immune function when deficiency is severe. An iron deficient woman might also be lacking in other aspects of her diet, so that the diagnosis can be a useful trigger for a more general discussion of healthy eating and lifestyle. In men, on the other hand, the finding of iron deficiency is much rarer and should prompt a careful search for sources of occult bleeding, including GIT cancer.

Who is at risk?

The obvious risk factor is simply being a woman - on its own hardly the working basis for a clinical protocol! Apart from gender, the most important single thing to check in the history is blood donation. There is a direct relationship between the frequency of giving blood and the prevalence of iron deficiency. Unfortunately blood banks do not routinely test donors for iron status (as distinct from anaemia), so it is vital that the family physician does. Heavy menstrual blood loss is another major risk, but the family physician needs to bear in mind the research showing that women cannot reliably tell whether their blood loss is heavy or not. The only helpful objective `sign' of heavy periods is soaking through or use of multiple pads. Pregnancy and lactation are periods of uniquely high iron demand, where a woman needs either the best of iron-rich diets or plentiful pre-existing iron stores to draw on, if she is to prevent herself becoming iron deficient.

Poor diet as a cause is important, though less so in adult medicine than in paediatrics. The usual causes of dietary inadequacy, such as being socioeconomically disadvantaged, having a physical illness which affects appetite or absorption and being institutionalised are all relevant. Immigrant families have been shown to have higher prevalence of iron deficiency than the general population. Teenagers are at particular risk, as this is a time when fad diets, the influence of the peer group and pressures to look slim all crash headlong into the increased iron requirements of growth and menstruation.

Not all iron is equal

As well as knowing which patient groups are at risk, it is very helpful if the family physician understands the concept of bioavailability. Not all iron is created equal when it comes to the body's ability to absorb it. In particular, the absorption of haem iron (meat, chicken, fish) is much greater than that of non-haem iron (vegetable and grain sources). On top of this, certain foods enhance non-haem iron absorption (vitamin C-rich foods, meat) whilst others inhibit it (phytates, tea). Thus vegetarians will have difficulty meeting their iron requirements unless they eat plenty of grains, nuts and legumes, which are the richer plant sources of iron. Any patient with marginal iron balance can be tipped into deficiency if they drink lots of tea with their main iron-containing meals. This is a particularly useful tip to offer the pregnant or vegetarian woman.

Testing for iron status

There is no evidence that routine laboratory testing for iron status is appropriate for the population as a whole.  However, where there are grounds to suspect the possibility of iron deficiency, it is a relatively straightforward process to confirm or exclude it. This would certainly include female blood donors and vegetarians.

By all means order a haemoglobin or full blood count, but know that a normal result does not in any way rule out the diagnosis. More persuasive evidence would be a fall in Hb from a previous reading (`relative anaemia') or an increase in the red cell distribution width. Both are early manifestations of iron deficiency anaemia, unlike microcytosis, which is a late sign.

The only reliable way to test for iron deficiency, however, is to assay iron stores directly, and for this purpose the serum ferritin is the measure of choice. A low serum ferritin (< 12 µgm/L) is diagnostic of iron deficiency, as there is no other condition that can produce this result. Where SF lies in the range 12-15 µgm/L the additional finding of a low transferrin saturation is helpful in confirming the diagnosis. Be aware however, that SF can be elevated in acute inflammation some cancers and liver disease. Hence a woman who happened to have a concurrent respiratory infection might return a normal SF despite having iron deficiency. Note that serum iron is a completely useless test for iron deficiency. Although it has some role in the work-up of iron overload disorders, it is completely unreliable in identifying patients with deficiency.

Practice tips

  • Not all iron is created equal - bioavailability is important.
  • Identify blood donors and routinely check their iron status.
  • Serum ferritin is the best test for iron deficiency, but it can be normal in iron deficient women who also have infection, liver disease and malignancy.
  • `Relative anaemia' and increased red cell distribution width are early signs of iron deficiency anaemia, but microcytosis is a late sign.
  • Advise patients with marginal iron status to avoid iron absorption inhibitors (tea and fibre) and to take enhancers (vitamin C-rich foods, meat) with the main iron-containing meal.

For comprehensive information on iron deficiency in adults, see the
 Clinical Management Guide   produced by the Australian Iron Status Advisory Panel

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