Full blood count and blood-film interpretation in children — structured clinical encounter

Station 1 — the printout that needs an age

Asked for my first move on a haemoglobin of 100, I would say I cannot interpret a paediatric value without the age band, because the same number is normal at the physiological nadir of infancy and abnormal in an older child. I would state the age aloud and read every value against age-specific paediatric reference intervals, not adult ranges, and I would read the blood film alongside the count. [1] [4]

Station 2 — the thriving infant at the nadir

Told the child is a thriving two-month-old, I would recognise this as the physiological anaemia of infancy. The haemoglobin falls from a high birth value to a trough around two to three months in a term baby as blood volume expands faster than red cell mass, fetal haemoglobin is switched off, and the short neonatal red cell lifespan limits supply. In a thriving, asymptomatic infant with a normal film, no work-up is needed; prematurity, pallor or an abnormal film would redirect me to a haemolysis or iron work-up. [1]

Station 3 — the toddler with microcytic anaemia

Given an eighteen-month-old with a haemoglobin of 72, a mean cell volume of 58, a high red cell distribution width and 700 millilitres of cow's milk a day, I would diagnose iron deficiency as the most likely cause. I would confirm with iron studies — a low ferritin and transferrin saturation with a high total iron-binding capacity — and I would treat with oral elemental iron at 3 to 6 milligrams per kilogram per day, expecting a reticulocyte rise within seven to ten days and continuing for three months after correction to replete stores, while reducing cow's milk intake. [5] [6]

Station 4 — the thalassaemia distinction

Asked how I would separate thalassaemia trait if the ferritin were replete, I would point to microcytosis out of proportion to a mild anaemia, a normal red cell distribution width with uniformly small cells, and a high red cell count. The Mentzer index, the mean cell volume divided by the red cell count, is above 13 in thalassaemia trait and below 13 in iron deficiency, and I would confirm with haemoglobin electrophoresis showing a raised haemoglobin A2 in beta-thalassaemia trait. [6]

Station 5 — the child with thrombocytopenia and the artefact

Given a well four-year-old with a platelet count of 12, petechiae and a normal film two weeks after a viral illness, I would diagnose immune thrombocytopenia. Before committing, I would confirm the count is genuine and not EDTA-dependent platelet clumping by reviewing the film and repeating in citrate. I would manage to the bleeding phenotype — observe if well, treat with steroids or intravenous immunoglobulin for bleeding or very low counts, per the American Society of Hematology 2019 guidance. Faced separately with a well child, no petechiae and a count of 8, I would suspect an artefact and repeat before any intervention. [8] [9]

Station 6 — the film that demands urgency

Finally, handed a film with blasts and a pancytopenia in a pale, bruising child, I would recognise acute leukaemia until proven otherwise. This is the urgent pathway: immediate paediatric oncology referral, fever precautions for the inevitable neutropenia, and a prompt marrow aspirate and trephine, without delay for elective review. I would close by reaffirming that a flagged count that looks only mildly abnormal can hide the cells that change everything today, which is why the film is the arbitrator. [8] [10]