Red blood cell
Red blood cell aggregates are counted as single cells by the automated analyzers used to run complete blood count tests. This leads to a markedly decreased red blood cell count and hematocrit and markedly elevated mean cell volume and mean cell hemoglobin concentration. Red cell agglutination also interferes with routine methods for blood typing and blood compatibility testing, which rely on agglutination reactions. People with red cell agglutination may exhibit spontaneous agglutination reactions during testing, leading to a false positive result. If the causative antibodies are only active at room temperature, the agglutination can be reversed by heating the blood sample to . People with warm autoimmune hemolytic anemia may exhibit red cell agglutination that does not resolve on warming.