Iron Deficiency

This is a fundamental, common and essential blood film appearance. The primary presenting feature will be a clinical history of fatigue, blood loss (or sometimes very non-specific, e.g. unwell). Morphologically, the striking abnormality is the microcytic, hypochromic anaemia. 

The main differentials for a micocytic, hypochromic anaemia are iron deficiency (the most common worldwide), lead poisioning (extremely rare - unless you are sitting the Part 2 exam, when its surprisingly common), and haemoglobinopathy. It is often tempting to say that the red cell ansiopoikilocytosis will help you tell the difference, but severe Iron deficiency can look trully awful on a blood film - especially if there have been transient attempts to treat this and the picture is somewhat dimoprhic. 

Remember - iron deficiency can occur in conjunction with other disorders! Don't miss the platelet count of 5 while concentrating on the red cell changes. Of course clinically these are linked - chronic bleeding from long term thromobcytopenia may well cause IDA. 

Lead posioning is easy to dsitinguish by the presence of prominent basophilic stippling. You can see examples of this in slide CW012. 

The most reliable way to tell between haemoglobinopathy and IDA (apart from experience of course...) is to look for classical findings of Hbopathy - such as sickle cells or C crystals, and look for classic signs of iron deficiency such as anisochromasia. Target cells will be present in both. Pencil cells (or elliptocytes) may be similarly common, so are not terribly reliable.

Anisochromasia is the difference in how well the cells are haemoglobinised. If the cells are uniform, with the same amount of haemoglobin (seen as a red clour on the stain - and hence the term anisochromasia, literally not- the same= colour) then it's most likely we are dealing with a haemoglobinopathy. In IDA, there will always be periods where there is adequate iron - usually after a patient has taken a supplement or had a good meal. These periods where iron is available will result in some red cells looking well haemoglobinised, almost normal. It is easy to mistake for post transfusion, but the picture won't be truly dimorphic in IDA. 

At the end, always say correlate with ferritin (and other haemotinics if required), and say if remains abnormal when iron replete, refer for specialist/genetic testing.