Expansion
Three cell lines, then the indices, then the film
Mnemonic
“One line or three” is the first question:
- One cell line affected points to a single process: bleeding or haematinic deficiency for anaemia, drugs or viral infection for neutropenia, immune destruction for thrombocytopenia
- All three (pancytopenia) points to marrow failure, destruction or sequestration
Then “the MCV sorts the anaemia”:
- Microcytic - iron deficiency, thalassaemia, sideroblastic, chronic disease
- Normocytic - acute blood loss, chronic disease, renal failure, haemolysis
- Macrocytic - B12 and folate, alcohol, liver disease, hypothyroidism, myelodysplasia, drugs
“TAILS” for macrocytosis: Thyroid, Alcohol and liver, Inherited (myelodysplasia), Liver, Spleen removed, plus B12 and folate.
Acute bleeding does not drop the haemoglobin immediately, because whole blood is lost; the fall appears with dilution over hours, which is why a normal haemoglobin never excludes significant haemorrhage.
Expansion
Read it in this order
- Haemoglobin, then the MCV to classify any anaemia
- White cell count, then the differential, since a normal total can conceal neutropenia with lymphocytosis
- Platelets, and check for clumping if the count is unexpectedly low
- Compare with previous results; the trend is more informative than any single value
- Request a blood film whenever the pattern is unexplained
One line or three
- Isolated anaemia: bleeding, haematinic deficiency, chronic disease, haemolysis, renal failure
- Isolated neutropenia: drugs, viral infection, autoimmune, ethnic benign neutropenia
- Isolated thrombocytopenia: immune thrombocytopenia, drugs, alcohol, viral
- Pancytopenia, being all three: marrow failure (aplasia, infiltration, myelodysplasia, B12 or folate deficiency), destruction (immune, disseminated intravascular coagulation), or sequestration (hypersplenism)
Traps
- Spurious values: platelet clumping from EDTA, a clotted or diluted sample, a drip arm
- Haemoconcentration masking anaemia in dehydration, so the haemoglobin falls after fluid resuscitation
- Acute bleeding does not drop the haemoglobin immediately, since whole blood is lost; it falls with dilution over hours
- A normal MCV with mixed iron and B12 deficiency, where the film shows a dimorphic picture
Urgent patterns: blasts on the film, neutrophils under 0.5, platelets under 20, or pancytopenia with fever, all warrant immediate haematology discussion.