Red blood cells
What it measures, and what changes the number.
The red blood cell count, sometimes called RBC or erythrocyte count, measures how many red cells are present in a given volume of blood. Red cells carry oxygen using the protein hemoglobin. The count is part of the complete blood count and is done by an automated analyzer.
It is read together with hemoglobin and hematocrit, which also describe red cell mass, and with the indices MCV, MCH, MCHC and RDW that describe cell size and content. Reticulocytes, young red cells, may be added to see how actively they are being produced.
The sample goes into an anticoagulant tube. Hydration, body position during the draw and a long tourniquet time can concentrate or dilute the blood slightly and shift the count. Results from different analyzers are broadly similar but not identical. Labs may label it Hematíes, Eritrocitos or RBC.
Often read alongside: Hemoglobin, Hematocrit, MCV, RDW, Reticulocytes