MPN Workshop of the Carolinas 2025 | The diagnostic approach for CMML: tests and techniques used

So, I see many, many CMML patients, and it’s quite a rare disease, but one of the things that we use to identify patients who may have CMML are their blood count trends. And so, in order to have or establish a diagnosis of CMML, patients need to have an absolute monocytosis of over 1,000 per microliter on their CBC. And they also have to have a relative monocytosis over 10% on serial blood counts. And these trends need to be persistent over a period of at least three months. Of course, we need a bone marrow biopsy. And the bone marrow biopsy usually will demonstrate some sort of bone marrow monocytosis. But in order to kind of distinguish reactive monocytosis from CMML-related monocytosis, sometimes you can use monocyte repartitioning techniques using flow cytometry, so looking at CD14 and CD16 staining. So in CMML, monocytes, classical monocytes are increased, so that’s the CD14-positive, CD16-negative fraction. And so that actually has a pretty high sensitivity and specificity for identifying CMML-related monocytes. And then also additional kind of cytogenetic or clonal abnormalities identified through somatic mutations can also help point to a diagnosis of CMML. And then it’s important to exclude certain types of rearrangements, specifically PDGFR rearrangements.

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