In this video lecture, Dr. Ilene C. Weitz discusses:
- The two distinct pathogenic mechanisms in cold agglutinin disease—cold-induced red cell agglutination and complement-mediated hemolysis—and how each contributes to clinical symptoms.
- The evaluation and diagnosis of CAD, including laboratory testing, bone marrow findings, and common specimen-handling pitfalls that can lead to false negative results.
- How treatment selection depends on the dominant clinical problem, including the roles of complement inhibition, B-cell-directed therapy, and supportive care.
Dr. Ilene C. Weitz is a Professor of Medicine at the Keck School of Medicine at the University of Southern California (USC). Her practice sites include, LAC+USC Medical Center, Keck Hospital of USC and USC Norris Cancer Hospital. Dr. Weitz is board certified in Internal Medicine and Hematology. She completed her medical degree at Medical College of Pennsylvania in Philadelphia, followed by an internship and residency in internal medicine at Cedars-Sinai Medical Center. She conducted a fellowship in hematology/oncology at Scripps Clinic and Research Foundation in La Jolla, California.
Dr. Weitz is a member of the Academy-Simmons College Honor Society, Alpha Omega Alpha, American Medical Women’s Association, Los Angeles County Medical Women’s Association, Alumni Associations of Medical College of Pennsylvania and Cedars-Sinai Medical Center, American Society of Hematology, and American Society of Clinical Oncology. She received the Morris Press Humanism Award in 1987 and the Golden Apple Outstanding Physician Educator Award in 1990 from Cedars-Sinai Medical Center, as well as the Outstanding Voluntary Faculty Award in the Division of Hematology from USC School of Medicine. Dr Weitz has delivered nationwide lectures and has been published in numerous journals, including American Journal of Clinical Pathology, Hepatology, Journal of Clinical Oncology, and American Journal of Hematology. She has also contributed eight book chapters or reviews.
(Video Lecture Summary)
Introduction
Dr. Ilene Weitz reviews the clinical manifestations, pathophysiology, and evolving treatment landscape of cold agglutinin disease (CAD). Using a patient case as a framework, she emphasizes that CAD is best understood as a disease with two interconnected but distinct mechanisms: cold-induced red blood cell agglutination and complement-mediated hemolysis. Recognizing which process is driving a patient’s symptoms is essential for selecting appropriate therapy.
A Case Illustrating the Complexity of CAD
Dr. Weitz presents the case of a 67-year-old woman who developed progressive anemia following COVID-19 infections. Her evaluation demonstrated laboratory evidence of hemolysis, a positive direct antiglobulin test for C3, a high cold agglutinin titer, and a low-grade clonal B-cell population in the bone marrow.
Although she initially deferred treatment, worsening anemia ultimately required transfusion support and treatment with sutimlimab. Later, she experienced severe cold-induced circulatory symptoms despite complement inhibition, illustrating how suppression of hemolysis does not necessarily eliminate symptoms caused by red blood cell agglutination.
Two Mechanisms, Two Clinical Problems
A central theme of the lecture is that CAD consists of two separate pathogenic processes.
The first is cold-induced agglutination of red blood cells caused by IgM antibodies. This process produces circulatory manifestations such as acrocyanosis, Raynaud phenomenon, livedo reticularis, pain, tissue ischemia, and, in severe cases, gangrene.
The second is complement-mediated hemolysis. Activation of the classical complement pathway leads to destruction of red blood cells and produces anemia, fatigue, dyspnea, jaundice, hemoglobinuria, and other consequences of ongoing hemolysis.
Dr. Weitz emphasizes that therapies targeting one mechanism may not adequately address the other, making treatment decisions more nuanced than simply controlling hemolysis.
Clinical Presentation and Disease Burden
Most patients present primarily with hemolytic anemia, often accompanied by only mild circulatory symptoms. Others experience both significant anemia and cold-induced circulatory manifestations. A smaller proportion present predominantly with circulatory symptoms despite relatively compensated hemolysis.
Dr. Weitz notes that disease severity does not correlate well with IgM levels. Patients may have severe anemia despite relatively modest monoclonal protein levels, while others with higher IgM levels may have milder disease.
She also discusses seasonal variation, observing that patients in warmer climates often present during colder months, whereas patients living in colder regions may experience symptoms throughout the year.
Thrombosis and Mortality Risk
The lecture highlights the growing recognition that CAD is associated with increased thromboembolic risk. Complement activation generates inflammatory mediators and promotes interactions between the complement and coagulation systems, contributing to both arterial and venous thrombosis.
Dr. Weitz reviews observational data demonstrating higher rates of thromboembolic events among patients with CAD compared with matched controls. She also notes evidence suggesting increased mortality and a younger age at death among patients with CAD, particularly in those who experience thrombotic complications.
Diagnostic Evaluation and Laboratory Pitfalls
Accurate diagnosis requires meticulous specimen handling. Dr. Weitz stresses that blood samples must be collected in pre-warmed tubes and maintained at warm temperatures until processing. Failure to do so can result in red blood cell agglutination within the specimen and potentially misleading laboratory results.
Diagnostic evaluation includes a complete hemolysis workup, direct antiglobulin testing, cold agglutinin titers, thermal amplitude studies, and bone marrow assessment for an underlying clonal lymphoproliferative disorder. She explains that in vivo, IgM antibodies bind red blood cells at lower temperatures and activate complement. As blood returns to body temperature, the IgM may dissociate, leaving complement proteins attached to the red cell surface. As a result, the direct antiglobulin test is typically positive for complement rather than IgM.
Traditional and B-Cell-Directed Therapies
Before the availability of complement inhibitors, management focused largely on supportive care and treatment of the underlying clonal B-cell disorder. Supportive measures include thermal protection, folate supplementation, transfusion support, plasmapheresis, and erythropoietin when appropriate. Dr. Weitz reviews B-cell-directed therapies such as rituximab and rituximab-bendamustine, which can reduce pathogenic IgM production by targeting the underlying clone. While these approaches can produce durable responses in some patients, complete responses are uncommon and onset of action may be slow.
She also notes that corticosteroids, splenectomy, IVIG, and several older therapies have little or no role in CAD management.
Complement Inhibition and the Impact of Sutimlimab
A major focus of the lecture is the emergence of complement inhibition as a treatment strategy. By targeting C1s and blocking activation of the classical complement pathway, sutimlimab rapidly suppresses hemolysis. Dr. Weitz reviews data from the CARDINAL and CADENZA trials demonstrating improvements in hemoglobin, bilirubin, haptoglobin, reticulocyte counts, LDH, and transfusion requirements. She also highlights improvements in fatigue and reductions in inflammatory markers such as IL-6. Importantly, she emphasizes that complement inhibition addresses the hemolytic component of CAD but does not eliminate the pathogenic IgM responsible for red blood cell agglutination and circulatory symptoms.
A Treatment Framework Based on the Dominant Mechanism
Dr. Weitz concludes by proposing a practical treatment framework centered on the patient’s predominant clinical problem.
Patients with minimal symptoms may be observed. Those with severe anemia who require rapid improvement are often candidates for complement inhibition with sutimlimab. In contrast, patients whose primary burden comes from cold-induced circulatory symptoms may benefit more from therapies that reduce pathogenic IgM production, such as rituximab-based treatment or plasmapheresis.
This distinction reflects the central message of the lecture: CAD involves two mechanisms and therefore raises two separate treatment questions. Effective management requires identifying which mechanism is driving symptoms and tailoring therapy accordingly..