Spurious automated red cell values in warm autoimmune hemolytic anemia

Two patients with warm autoantibodies to their red cells had a mean cell volume artifactually elevated by red cell agglutination. Red cell size distribution histograms directly showed doublets and triplets of normal-size red cells. This phenomenon is similar to the spurious macrocytosis previously reported due to cold agglutinins, but was not reversible by warming.