CD33

Immunity

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No Fasting Required

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Flow cytometry panel of immune cell surface markers.

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CD33 Test Information Guide

Why is it done?
- CD33 is a cell surface antigen (marker) used to identify and classify myeloid cells and is primarily performed to detect and diagnose acute myeloid leukemia (AML) and other hematologic malignancies
- Detection of abnormal myeloid populations: Identifies leukemic blasts and abnormal cell populations in bone marrow and peripheral blood samples
- Flow cytometry analysis: Used as part of multi-parameter flow cytometry panels to characterize immature myeloid cells and establish immunophenotypes
- Diagnosis and classification: Helps differentiate AML subtypes and other myeloproliferative disorders from lymphoid malignancies
- Minimal residual disease (MRD) monitoring: Tracks leukemic cell populations during and after treatment to assess treatment response
- Typical timing: Performed when AML is suspected, at initial diagnosis, during treatment monitoring, and for surveillance in remission
Normal Range
- CD33 expression pattern: CD33 is normally expressed on myeloid lineage cells, monocytes, and granulocytes in peripheral blood and bone marrow
- Normal percentage: CD33+ cells typically comprise 3-8% of bone marrow cells and represent normal myeloid differentiation
- Negative/Normal result: Indicates absence of abnormal myeloid blast population; normal myeloid maturation pattern observed
- Positive/Abnormal result: CD33+ blast population >20% or abnormal immunophenotype pattern indicates likely acute myeloid leukemia or myelodysplastic disorder
- Intensity of expression: Flow cytometry measures fluorescence intensity; abnormal intensity (too dim or too bright) may indicate aberrant expression patterns
- Units: Reported as percentage (%) of cells or as median fluorescence intensity (MFI) in flow cytometry analysis
Interpretation
- CD33+ blast population >20%: Highly suggestive of acute myeloid leukemia (AML); most AML cases express CD33 (>80% of cases)
- CD33+ with CD13, CD15, HLA-DR co-expression: Typical myeloid immunophenotype confirming myeloid lineage; abnormal antigen expression patterns help classify AML subtype
- CD33 negative or low expression: May indicate acute promyelocytic leukemia (APL/AML-M3) or rare CD33-negative AML subtypes; requires correlation with other markers
- Abnormal maturation pattern: Disproportionate CD33+ population without normal differentiation progression suggests myelodysplastic syndrome (MDS) or AML
- Minimal residual disease (MRD) <0.1%: Indicates good treatment response and improved prognosis during therapy monitoring
- Factors affecting interpretation:
  - Sample quality and timing (perform within 24-48 hours)
  - Flow cytometry instrument calibration and antibody panels used
  - Concurrent cytochemical staining (myeloperoxidase, Auer rods) and molecular findings
  - Clinical context and morphologic findings on bone marrow aspirate/biopsy
Associated Organs
- Primary organ systems involved:
  - Bone marrow: Primary site of hematopoiesis where CD33+ myeloid precursors originate
  - Blood: Peripheral circulation where mature myeloid cells express CD33
  - Lymphatic system: Lymph nodes and spleen may be affected in leukemia
- Medical conditions commonly associated with abnormal CD33 results:
  - Acute myeloid leukemia (AML): CD33+ in 80-95% of cases; most common malignancy detected
  - Myelodysplastic syndrome (MDS): Abnormal myeloid differentiation patterns with increased blasts
  - Chronic myeloid leukemia (CML): May show increased myeloid population but different immunophenotype pattern
  - Acute promyelocytic leukemia (APL/AML-M3): CD33 typically negative or low expression
  - Myeloproliferative neoplasms: Polycythemia vera, essential thrombocythemia with abnormal myeloid populations
- Potential complications and risks associated with abnormal results:
  - Bone marrow failure: Progressive anemia, thrombocytopenia, and neutropenia from leukemic infiltration
  - Infection: Severe immunosuppression from decreased normal white blood cells
  - Bleeding: Thrombocytopenia and coagulopathy from leukemic cells and tumor lysis
  - Leukostasis: Complications from high blast counts causing vascular occlusion
  - Extramedullary involvement: Leukemic infiltration of organs (liver, spleen, CNS, skin)
Follow-up Tests
- Additional tests recommended when CD33 is abnormal:
  - Complete immunophenotyping: Additional flow cytometry markers (CD13, CD15, CD34, HLA-DR, CD7, CD19) to classify AML subtype
  - Cytochemical studies: Myeloperoxidase (MPO), Auer rods to confirm myeloid lineage
  - Cytogenetic analysis: Karyotyping to identify chromosomal abnormalities and prognostic risk stratification
  - Molecular testing: FLT3, NPM1, CEBPA, IDH1/2 mutations for AML classification and prognosis
  - Bone marrow aspirate and biopsy: Morphologic evaluation and blast percentage determination
  - Complete blood count (CBC): Assess hemoglobin, platelets, and white blood cell counts
- Monitoring frequency during treatment:
  - Weekly to bi-weekly during active chemotherapy induction phase
  - After chemotherapy cycles to assess response (post-cycle 1 and 2)
  - Monthly during consolidation therapy to detect early relapse
  - Every 3-6 months during maintenance therapy or long-term follow-up
- Related complementary tests:
  - CD33/CD13 antigen co-expression panels for myeloid lineage confirmation
  - CD34 (stem cell marker) combined with CD33 to identify immature blasts
  - HLA-DR expression to identify aberrant phenotypes associated with poor prognosis
  - CD117, CD13, CD15 co-expression analysis for AML subtype determination
Fasting Required?
- Fasting required: No
- CD33 is a flow cytometry-based test performed on blood and bone marrow samples; fasting is not required for sample collection
- Patient preparation requirements:
  - No fasting required prior to blood draw
  - Routine blood draw or bone marrow aspiration may be performed any time of day
  - For bone marrow aspiration: Local anesthetic may be used; inform physician of bleeding disorders or anticoagulant use
- Medication considerations:
  - No specific medications need to be held before CD33 testing
  - If patient is on anticoagulants (warfarin, heparin) or antiplatelet agents (aspirin), inform phlebotomist prior to collection
  - Chemotherapy drugs do not interfere with CD33 testing; continue all prescribed medications as directed
- Special instructions:
  - Samples must be processed within 24-48 hours of collection for optimal results
  - EDTA (purple-top) or sodium heparin tubes used for flow cytometry
  - Room temperature storage preferred; avoid refrigeration or freezing
  - For bone marrow samples: Specimen integrity is critical; communicate urgency to laboratory

How our test process works!