In this video lecture, Dr. Sigbjørn Berentsen discusses:
- How to distinguish cold agglutinin disease from cold agglutinin syndrome and from incidentally detected cold agglutinins without hemolysis or symptoms.
- The diagnostic role of hemolysis labs, blood smear findings, polyspecific and monospecific direct antiglobulin testing, and cold agglutinin titers.
- Why serum studies, bone marrow biopsy, flow cytometry, and careful sample handling are important in confirming the diagnosis and identifying the underlying clonal B-cell disorder.
Sigbjørn Berentsen (MD, PhD) graduated in 1973 from the University of Bergen, Norway, and received his PhD in 2004; title of the thesis: “Primary chronic cold agglutinin disease”. He had his training in internal medicine at Haugesund Hospital and Stavanger University Hospital, and his hematology training at St. Olav University Hospital (Trondheim) and Haukeland University Hospital (Bergen). He has held positions as a consultant hematologist at Haugesund Hospital, Haukeland University Hospital, and Oslo University Hospital, and he was an associate professor at the University of Bergen 2004-2016.
Dr. Berentsen has authored more than 100 articles in PubMed-indexed journals including Blood, Haematologica, New England Journal of Medicine, and Lancet Haematology, as well as a couple of major textbook chapters. He has been interested in autoimmune hemolytic anemia (AIHA), lymphoproliferative disorders, and complement-mediated anemias. His current main field of research is cold agglutinin disease (CAD), in which he has authored observational studies, reviews, most trials of B-cell targeting therapies, and several studies on complement inhibition. He coauthored the international consensus work on AIHA, and he is also an author of the CAD section in UpToDate and a medical advisor of the CAD Foundation.
(Video Lecture Summary)
Introduction
Dr. Sigbjørn Berentsen provides an overview of the diagnosis of cold agglutinin disease, beginning with key concepts that help distinguish clinically meaningful cold agglutinins from incidental findings. He emphasizes that cold agglutinin pathogenicity depends more on biological activity than titer alone, especially thermal amplitude, antigen specificity, IgM structure, and clonality.
Cold Agglutinin Disease vs. Cold Agglutinin Syndrome
A central distinction in the lecture is between cold agglutinin disease and cold agglutinin syndrome. Cold agglutinin disease is described as a well-defined clinicopathologic entity caused by a non-malignant clonal B-cell disorder of the bone marrow. In contrast, cold agglutinin syndrome is secondary to another clinical condition, such as specific infections, low-grade non-Hodgkin lymphoma, other malignancies, or autoimmune disease such as SLE. Dr. Berentsen also notes that individuals with incidentally detected cold agglutinins but no hemolysis or clinical symptoms do not have either CAD or cold agglutinin syndrome.
Clinical Presentation and Pathophysiology
Dr. Berentsen explains that the clinical picture should guide the diagnostic process. Hemolysis in cold agglutinin disease is complement-dependent and mainly extravascular, occurring largely through C3b-mediated clearance of red cells in the liver. In severe cases or acute exacerbations, complement activation may proceed into the terminal pathway, causing some intravascular hemolysis.
He also distinguishes hemolytic features from peripheral circulatory symptoms such as acrocyanosis, Raynaud-like symptoms, livedo reticularis, and rarely ulceration or gangrene. These circulatory symptoms are not complement-mediated and are related to red blood cell agglutination in the acral circulation.
Diagnostic Criteria and Testing
Dr. Berentsen outlines the required diagnostic criteria for cold agglutinin disease: chronic hemolysis, a positive polyspecific direct antiglobulin test, a monospecific DAT strongly positive for C3d, a significant cold agglutinin titer, and no overt malignant disease or relevant infection explaining the findings.
He emphasizes that the DAT is not a test for hemolysis itself. Hemolysis should be established through markers such as LDH, bilirubin, haptoglobin, reticulocytes, and blood smear findings. The DAT is used to establish autoimmune pathogenesis. If the polyspecific DAT is positive, a monospecific or extended DAT is mandatory.
Cold Agglutinin Titer and Sample Handling
A key practical point is that the typical DAT pattern in CAD, positive for C3 only or strongly positive for C3d, is not sufficient by itself to diagnose cold agglutinin disease. A significant cold agglutinin titer must also be demonstrated.
Dr. Berentsen stresses that sample handling is essential. Blood specimens must be kept at 37 to 38°C until serum or plasma has been separated from the clot or cell pellet. Otherwise, the cold agglutinin may bind to the cells and be missed, or the measured titer may be falsely low.
Confirmatory Studies
Once cold agglutinin disease is diagnosed, Dr. Berentsen recommends serum protein electrophoresis and immunofixation. The typical finding is a monoclonal IgM kappa protein, although the monoclonal spike may be small and IgM levels may be normal.
Bone marrow biopsy and flow cytometry are also important, especially before treatment. Bone marrow evaluation may identify a cold agglutinin-associated lymphoproliferative disorder, though Dr. Berentsen notes that interpretation can be difficult and is improved when reviewed by experienced hematopathologists. Flow cytometry usually demonstrates a clonal B-cell kappa disorder.
Case Example
Dr. Berentsen presents a 65-year-old woman with fatigue, severe anemia, laboratory evidence of hemolysis, red blood cell agglutinates on smear, a positive polyspecific DAT, strongly positive C3d on monospecific DAT, and a high cold agglutinin titer. Although her symptoms worsened after COVID-19 infection, further testing showed monoclonal IgM kappa, low complement C4, and bone marrow findings consistent with cold agglutinin-associated lymphoproliferative disorder. The final diagnosis was cold agglutinin disease with an infection-triggered exacerbation, not secondary cold agglutinin syndrome due to COVID-19.
Conclusion
Dr. Berentsen concludes by emphasizing awareness of the disease, targeted history and physical examination, and a structured diagnostic algorithm. A monospecific DAT is mandatory after a positive polyspecific DAT, but the C3-positive DAT pattern is not pathognomonic. A significant cold agglutinin titer is required, sample handling must be correct, and bone marrow biopsy is important at least before treatment. preeclampsia and HELLP, and pregnancy-associated TMAs such as TTP, differ in timing and persistence. Preeclampsia usually arises after 20 weeks, HELLP in the third trimester, while TTP may present at any time, including postpartum. The key differentiator is a severely reduced ADAMTS13 activity (<20%) in TTP. Routine labs may not distinguish these entities, but ADAMTS13 testing and attention to maternal end-organ damage guide diagnosis. Emerging therapies like including recombinant ADAMTS13 and targeted agents offer promising avenues for improving maternal and fetal outcomes.