Editing Red blood cell (section)

=== Tests ===
[[File:Poikilocytes - Red blood cell types.jpg|thumb|Variations of red blood cell shape, overall termed [[poikilocytosis]]]]
Several [[blood test]]s involve red blood cells. These include a ''RBC count'' (the number of red blood cells per volume of blood), calculation of the [[hematocrit]] (percentage of blood volume occupied by red blood cells), and the [[erythrocyte sedimentation rate]]. The [[blood type]] needs to be determined to prepare for a [[blood transfusion]] or an [[organ transplantation]].

Many diseases involving red blood cells are diagnosed with a [[blood film]] (or peripheral blood smear), where a thin layer of blood is smeared on a microscope slide. This may reveal [[poikilocytosis]], which are variations in red blood cell shape. When red blood cells sometimes occur as a stack, flat side next to flat side. This is known as ''[[rouleaux]] formation'', and it occurs more often if the levels of certain serum proteins are elevated, as for instance during [[inflammation]].