The full blood count (complete blood count) is ordered so often that it is easy to glance at the flagged values and move on. A structured read can uncover diagnoses hiding in plain sight.
Red cells
Start with haemoglobin, then use the mean cell volume (MCV) to classify anaemia. A raised red cell distribution width (RDW) suggests a mixed or evolving picture.
Anaemia by MCV:
- Microcytic – iron deficiency, thalassaemia trait, anaemia of chronic disease
- Normocytic – acute blood loss, chronic disease, kidney disease
- Macrocytic – B12 or folate deficiency, alcohol, liver disease, some drugs
White cells
Always read the differential, not just the total. Neutrophilia points towards bacterial infection, steroids or stress; lymphocytosis to viral infection or lymphoproliferative disease; eosinophilia to allergy, parasites or drug reactions.
Platelets
An unexpectedly low platelet count in a well patient may be pseudothrombocytopenia, caused by clumping in EDTA tubes. A blood film or a repeat sample in a citrate tube will clarify it.
“When the numbers do not make sense, ask for the blood film.”
Compare with previous results whenever possible — the trend is often more informative than a single value.
This article is for education only and does not replace clinical judgement or local guidelines.
