Detection of minimal/measurable residual disease (MRD) in acute myeloid leukemia (AML) is important for guiding patient‐specific clinical management. Natural killer (NK) cells can express various markers not typically associated with NK lineage, potentially confounding the detection of MRD by flow cytometry. We have observed CD33 expression on NK cells when evaluating for AML MRD in routine clinical practice in multiple patient samples. To characterize CD33 expression on NK cells, 40 peripheral blood or bone marrow samples with NK cells present at >5% of lymphocytes were selected for further assessment of NK cell phenotype and CD33 expression. Seven of the 40 samples (17.5%) were found to have CD33 expression on at least 5% of the NK cells. The CD33‐positive NK cell population accounted for an average of 11.4% of NK cells (median 11.9%, range 8.0–15.3%) and 2.2% of total white cells (median 1.1%, range 0.1‐10.1%). This NK cell subset expressed bright CD2, bright CD56, and dim CD16. On average, CD33 expression on NK cells was dimmer than on monocytes (mean median fluorescence intensity ratio 0.4; range 0.1‐1.0). This study characterizes expression of CD33 on NK cells. Recognition of this pattern of antigen expression is critical in evaluating samples for MRD in patients with myeloid neoplasms, particularly AML.
Retroperitoneal hemorrhage with associated intramural hemorrhage into the renal pelvis and proximal ureter is a well documented complication of coagulation defects. The urographic characteristics of this condition have been well documented by several authors [1-4], but to our knowledge the computed tomographic (CT) findings in patients with this condition have not been reported previously. We describe the CT findings in 2 such cases; one related to thrombocytopenia in leukemia, and the other to anticoagulant therapy in a patient with Budd-Chiari syndrome.
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