CAD study highlights need for more sensitive bone marrow testing
Researchers found small immune cell clones in most confirmed cases
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Cold agglutinin disease (CAD) rarely occurs without abnormal immune cell growth in the bone marrow or blood, but this abnormal cell growth is often hard to detect with standard assessments, a new study shows.
“Our data underscore the importance of a comprehensive and sensitive approach when evaluating bone marrow samples in patients with suspected CAD,” the researchers wrote, noting that CAD “scarcely occurs in the absence of an underlying [abnormal immune cell growth]; however, this [cell] clone is often too small to be detected by standard [tissue analysis].”
The study, “Bone Marrow Pathology in Cold Agglutinin-Mediated Autoimmune Hemolytic Anemia: A Study of 56 Cases,” was published in the European Journal of Haematology.
CAD can involve abnormal B-cell growth
CAD is a rare autoimmune disorder marked by self-reactive antibodies, known as cold agglutinins, that stick to red blood cells at low temperatures. Antibodies are immune proteins produced by B-cells, a specialized type of immune cell.
The disease can occur on its own as primary CAD, which is typically associated with a slow but abnormal growth of a single B-cell population, or clonal growth, in the blood and/or the bone marrow. The bone marrow is the spongy tissue in bones where all blood and immune cells are produced. When cold agglutinin-related anemia occurs secondary to an underlying condition, such as an infection, blood cancer, or autoimmune condition, it is known as cold agglutinin syndrome, or CAS.
A few years back, the World Health Organization (WHO) included CAD in its classification of blood cancers and related blood disorders, defining it by several clinical features and evidence of a clonal B-cell disorder. Among the desirable diagnostic criteria is the presence of CAD-associated lymphoproliferative disease (CAD-LPD), which is based on specific tissue, cell, and genetic features.
That new WHO classification was based mainly on a previous study in Norway that analyzed bone marrow samples from 54 people with well-defined CAD.
Study reviews bone marrow samples in CAD
Spurred by that new classification, a team led by scientists in the Netherlands analyzed stored bone marrow biopsies from 56 people being evaluated for CAD who received care at their center between 2000 and 2025.
None had signs of CAD related to infection or autoimmune disease, but some had underlying B-cell cancers. Most (70%) were women, and their mean age at diagnosis was 63 years.
Analyses of bone marrow samples under a microscope, an approach called histology, showed that slightly more than half of patients, or 59%, had evidence of clonal B-cell growth. However, this rate increased to 84% when the researchers used more sensitive tests, including genetic sequencing and flow cytometry, which analyzes the makeup of individual cells.
“We confirmed that the occurrence of symptomatic cold agglutinins in chronic [CAD] in the absence of an underlying clonal [B-cell growth] is highly uncommon,” the researchers wrote.
Histology may have missed this abnormal growth because CAD-associated B-cell clones in the bone marrow are often too small to reliably see on microscope slides, the team noted.
“Our findings do indicate that the CAD-associated bone marrow clone is usually (very) small,” the researchers wrote.
This highlights the importance of more sensitive tests when analyzing bone marrow samples from people with CAD or suspected CAD.
WHO criteria missed many confirmed cases
Of note, even though nearly all confirmed CAD patients had evidence of abnormal B-cell growth, only five (11%) of the 45 people fulfilling all essential WHO CAD diagnostic criteria met the criteria for CAD-LPD. In most other patients, the specific patterns of B-cell growth didn’t line up with the criteria outlined by the WHO based on the Norwegian study.
“In our CAD [patient group], the [WHO] criteria did not fit a substantial proportion of cases due to lack of concordance with the desirable CAD-LPD definition,” the scientists wrote.
This discrepancy may be due to the Norwegian study’s more stringent selection criteria, which included only well-documented primary CAD cases. By contrast, the researchers in the current study were looking at all available bone marrow biopsies from people being evaluated for CAD.
Pathologists, or doctors who specialize in studying tissues and fluids, “should be aware that the lymphoproliferation underlying CAD may represent a very small clone and is less [uniform] than previously suggested, rather than relying too rigidly on the [WHO] CAD-LPD criterium,” the team wrote. “For clinicians evaluating [CAD] cases, it is crucial to take an integral approach, incorporating clinical data as well as a platform of sensitive clonality detection techniques.”
