How to Read Your CBC Report

Hemoglobin is a concentration, not a headcount of your red cells. It reads high when you are dry, low when fluid floods in, and can sit perfectly normal while your iron quietly runs out.

The white blood cell count is a single headcount that lumps five different immune cells into one number. It rises for plenty of reasons that have nothing to do with being sick.

Red blood cell count is a headcount of the cells in a drop of blood. It tells you how many there are, not how much oxygen each one can carry, which is why the number only makes sense beside hemoglobin and MCV.

Neutrophils are the body's first and most numerous cleanup crew. Because they make up more than half the white blood cell count, when the total moves, this is usually the line that moved it.

Hematocrit is the share of your blood that is red cells, read off a spun tube as a packed layer. It climbs when you are dry and dips when fluid floods in, which is why it almost never travels alone.

MCV is the average size of your red blood cells. Small cells lean toward iron trouble, large cells toward B12 or folate, and a crowd of both can average out to a number that looks fine.

Platelets are the patches your blood carries to seal small leaks. The count rises and falls for real reasons, but one of the most common low results isn't your body at all, it's the tube.

MCH is the average amount of hemoglobin packed into one red blood cell. It tracks the MCV so faithfully it rarely says anything new, and being an average, it hides the pale cells mixed in with the rich ones.

MPV is the average size of your platelets, and size hints at age. A tray of big, fresh platelets usually means the marrow just fired up to replace ones being used or destroyed.

MCHC is how densely hemoglobin is packed inside a red cell, not how much each cell carries. The cell can only pack it so tight, so a high MCHC reads less like a finding and more like a reason to recheck the tube.

RDW measures how much your red blood cells vary in size. It often climbs before hemoglobin or MCV drift out of range, and it splits two anemias that otherwise look identical.

Reticulocytes are the red cells that just left the marrow. The count is an arrival rate, not a population, and in anemia it answers the one question the other red-cell numbers can't: is the marrow even responding?

Lymphocytes are the immune system's record-keepers. They are the line that climbs during a viral illness, often while the total white count sits still.

Monocytes are the white cell counted on its way to a new job. The blood number catches them in transit, before they reach the tissues and change both their name and their work.

Eosinophils are the immune line built for parasites that also fires at pollen. They are usually a small slice of the white count, and the slice that swells in allergic disease.

Basophils are the smallest fraction of the white count, so small that a low reading is usually noise. The result that carries weight is a high one that holds across draws.