Red cell agglutination

In hematology, red cell agglutination or autoagglutination is a phenomenon in which red blood cells clump together, forming aggregates. It is caused by the surface of the red cells being coated with antibodies.[1]: 98  This often occurs in cold agglutinin disease, a type of autoimmune hemolytic anemia in which people produce antibodies (termed cold agglutinins) that bind to their red blood cells at cold temperatures and destroy them. People may develop cold agglutinins from lymphoproliferative disorders, from infection with Mycoplasma pneumoniae or Epstein–Barr virus, or idiopathically (without any apparent cause). Red cell agglutination can also occur in paroxysmal nocturnal hemoglobinuria[2]: 13 [3] and warm autoimmune hemolytic anemia.[4]: 88  In cases of red cell agglutination, the direct antiglobulin test can be used to demonstrate the presence of antibodies bound to the red cells.[3]

This article is about the hematologic condition. For the use of red cell agglutination as a testing method, see hemagglutination.
Red cell agglutination in a patient with cold agglutinin disease.

Interference with laboratory tests

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.[5]: 32–3  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.[6]: 141, 262  If the causative antibodies are only active at room temperature, the agglutination can be reversed by heating the blood sample to 37 °C (99 °F). People with warm autoimmune hemolytic anemia may exhibit red cell agglutination that does not resolve on warming.[4]: 88 

References
  1. Bain, BJ (20 January 2015). Blood Cells: A Practical Guide (5 ed.). John Wiley & Sons. ISBN 978-1-118-81733-9.
  2. Hematology and Clinical Microscopy Committee (2019). "Blood cell identification" (PDF). Hematology and Clinical Microscopy Glossary. College of American Pathologists. Archived (PDF) from the original on 2019-06-28. Retrieved 2020-06-25.
  3. Quist, Erin; Koepsell, Scott (2015). "Autoimmune Hemolytic Anemia and Red Blood Cell Autoantibodies". Archives of Pathology & Laboratory Medicine. 139 (11): 1455–8. doi:10.5858/arpa.2014-0337-RS. PMID 26516943.
  4. Kottke-Marchant, K; Davis, B (6 June 2012). Laboratory Hematology Practice. John Wiley & Sons. ISBN 978-1-4443-9857-1.
  5. Bain, BJ; Bates, I; Laffan, MA (2017). Dacie and Lewis Practical Haematology (12 ed.). Elsevier Health Sciences. ISBN 978-0-7020-6925-3.
  6. Denise M Harmening (30 November 2018). Modern Blood Banking & Transfusion Practices. F.A. Davis. ISBN 978-0-8036-9462-0.
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