Haematology — Red Cell & Indices

Convert a reticulocyte percentage into an absolute count in ×10⁹/L — the number that tells you whether the marrow is actually responding.

Correct the reticulocyte percentage for anaemia by scaling it to a reference haematocrit of 45%, so the marrow response can be judged fairly.

Estimate the haematocrit as three times the haemoglobin — the rule of three — and see the anaemias in which that approximation stops holding.

Convert haemoglobin between g/dL, g/L and mmol/L — using the globin monomer mass, which is why SI reports read 8 to 11 mmol/L rather than 2 to 3.

Calculate mean corpuscular haemoglobin from haemoglobin and red cell count, and see why it usually tracks MCV rather than adding new information.

Calculate MCHC from haemoglobin and haematocrit, and learn why a genuinely high result is rare enough to demand a blood film first.

Calculate mean corpuscular volume from haematocrit and red cell count, and read the microcytic-normocytic-macrocytic split correctly.

Screen a microcytic anaemia toward thalassaemia trait or iron deficiency using MCV and red cell count, before confirming with ferritin or haemoglobin electrophoresis.

Calculate the RPI by correcting the reticulocyte count for both anaemia and the longer circulating lifespan of prematurely released reticulocytes.