FLOW CYTOMETRY QUESTIONS WITH CORRECT
ANSWERS 2026\2027
Immunophenotyping - CORRECT ANSWERS -This can be done on tissue section (fresh or fixed
tissue), cell suspension, etc. An example is the detection of tumor marker, such as in the
diagnosis of leukemia. It involves the labelling of white blood cells with antibodies directed
against surface proteins on their membrane. By choosing appropriate antibodies, the
differentiation of leukemic cells can be accurately determined. The labelled cells are processed
in a flow cytometer, a laser-based instrument capable of analyzing thousands of cells per
second. The whole procedure can be performed on cells from the blood, bone marrow or spinal
fluid in a matter of a few hours.
Immunophenotyping Specimen Processing - CORRECT ANSWERS -The cells from the blood,
bone marrow or spinal fluid in a matter of a few hours. Do NOT centrifuge. Transport
temperature: Room temperature. Specimen stability: Sodium heparin tube stable for 48 hours
at room temperature. Lavender (potassium EDTA) tubes are also acceptable for TBCS testing but
with a limited stability of 30 hours. Rejection criteria: Sample stability exceeded, clotted
specimens, poor viability.
Information that can be provided by immunophenotyping - CORRECT ANSWERS -malignant cells
were positive for CD19, CD10, dimCD20, CD45, HLA-DR, and λ immunoglobulin light chain.
There was no co-expression of CD5 or CD23 by the monoclonal B-cell population."
HLA alloantibody - CORRECT ANSWERS -Collect: Serum Sep. Tube-SST (GOLD), 7 days chilled, To
screen patients on bone marrow, renal, cardiac and liver transplant programs and transfusion
dependent patients for the presence of pre-existing anti-HLA antibodies. Donor-specific anti-
HLA antibodies may be associated with transplant rejection.
Solid Organ Transplant - CORRECT ANSWERS -Two classes of HLA antigens • Class I (HLA-A,B and
C) expressed on most cells of the body (T cells and B cells) • Class II (HLA-DR, DQ and DP)
expressed primarily on antigen presenting cells (eg, monocytes, B cells)
, Clinical Impact of HLA antibodies - CORRECT ANSWERS -• Hyperacute rejection - associated with
high levels of donor specific HLA antibody pre-transplant • Prolonged wait times for highly
sensitized • Biomarkers of increased risk for immunologic complications post-transplant • Post-
transplant de novo HLA antibody associated with poorer outcomes • For these reasons,
histocompatibility laboratories carry out detailed characterization of the HLA antibody
repertoire of transplant candidates
Flow Cytometry Cross Match - CORRECT ANSWERS -• When a potential donor is identified and
determined not to possess any unacceptable HLA antigens, a final test is done to confirm
compatibility - the crossmatch • The Flow cytometry crossmatch is the most sensitive
crossmatch test available and has replace cell base crossmatch testing in many laboratories
Monitoring depletion T and B lymphocyte patients - CORRECT ANSWERS -CD34 stem/progenitor
cell enumeration • Monitoring depletion of T and/or B lymphocytes in patients receiving
antibody therapies for treatment of rejection • Monitoring immune reconstitution post bone
marrow transplant
specimen collection for PID - CORRECT ANSWERS -specimens are processed within twenty-four
hours of collection. Specimens should be sent at room temperature
-Peripheral Blood for CD4 Lymphocytes and Fetal Erythrocyte Quantitation tests:
Draw one lavender (EDTA) tube, 3-5 mL. Maintain the specimen at room temperature.
Send sample at room (ambient) temperature.
Must be run within 48 hours of collection.
-Bone Marrow:Dispense the marrow into an ACD-A (yellow top) tube and mix thoroughly.
Submit a peripheral blood smear, patient history and clinical information; differential diagnosis
and a CBC/differential count if available.
-Fine Needle Aspiration:Perform
The number of cells harvested in any given FNA procedure varies greatly.
Multiple aspirations are usually better than single aspiration of the site. Single aspirate
specimens often contain too few leukocytes for satisfactory analysis.
ANSWERS 2026\2027
Immunophenotyping - CORRECT ANSWERS -This can be done on tissue section (fresh or fixed
tissue), cell suspension, etc. An example is the detection of tumor marker, such as in the
diagnosis of leukemia. It involves the labelling of white blood cells with antibodies directed
against surface proteins on their membrane. By choosing appropriate antibodies, the
differentiation of leukemic cells can be accurately determined. The labelled cells are processed
in a flow cytometer, a laser-based instrument capable of analyzing thousands of cells per
second. The whole procedure can be performed on cells from the blood, bone marrow or spinal
fluid in a matter of a few hours.
Immunophenotyping Specimen Processing - CORRECT ANSWERS -The cells from the blood,
bone marrow or spinal fluid in a matter of a few hours. Do NOT centrifuge. Transport
temperature: Room temperature. Specimen stability: Sodium heparin tube stable for 48 hours
at room temperature. Lavender (potassium EDTA) tubes are also acceptable for TBCS testing but
with a limited stability of 30 hours. Rejection criteria: Sample stability exceeded, clotted
specimens, poor viability.
Information that can be provided by immunophenotyping - CORRECT ANSWERS -malignant cells
were positive for CD19, CD10, dimCD20, CD45, HLA-DR, and λ immunoglobulin light chain.
There was no co-expression of CD5 or CD23 by the monoclonal B-cell population."
HLA alloantibody - CORRECT ANSWERS -Collect: Serum Sep. Tube-SST (GOLD), 7 days chilled, To
screen patients on bone marrow, renal, cardiac and liver transplant programs and transfusion
dependent patients for the presence of pre-existing anti-HLA antibodies. Donor-specific anti-
HLA antibodies may be associated with transplant rejection.
Solid Organ Transplant - CORRECT ANSWERS -Two classes of HLA antigens • Class I (HLA-A,B and
C) expressed on most cells of the body (T cells and B cells) • Class II (HLA-DR, DQ and DP)
expressed primarily on antigen presenting cells (eg, monocytes, B cells)
, Clinical Impact of HLA antibodies - CORRECT ANSWERS -• Hyperacute rejection - associated with
high levels of donor specific HLA antibody pre-transplant • Prolonged wait times for highly
sensitized • Biomarkers of increased risk for immunologic complications post-transplant • Post-
transplant de novo HLA antibody associated with poorer outcomes • For these reasons,
histocompatibility laboratories carry out detailed characterization of the HLA antibody
repertoire of transplant candidates
Flow Cytometry Cross Match - CORRECT ANSWERS -• When a potential donor is identified and
determined not to possess any unacceptable HLA antigens, a final test is done to confirm
compatibility - the crossmatch • The Flow cytometry crossmatch is the most sensitive
crossmatch test available and has replace cell base crossmatch testing in many laboratories
Monitoring depletion T and B lymphocyte patients - CORRECT ANSWERS -CD34 stem/progenitor
cell enumeration • Monitoring depletion of T and/or B lymphocytes in patients receiving
antibody therapies for treatment of rejection • Monitoring immune reconstitution post bone
marrow transplant
specimen collection for PID - CORRECT ANSWERS -specimens are processed within twenty-four
hours of collection. Specimens should be sent at room temperature
-Peripheral Blood for CD4 Lymphocytes and Fetal Erythrocyte Quantitation tests:
Draw one lavender (EDTA) tube, 3-5 mL. Maintain the specimen at room temperature.
Send sample at room (ambient) temperature.
Must be run within 48 hours of collection.
-Bone Marrow:Dispense the marrow into an ACD-A (yellow top) tube and mix thoroughly.
Submit a peripheral blood smear, patient history and clinical information; differential diagnosis
and a CBC/differential count if available.
-Fine Needle Aspiration:Perform
The number of cells harvested in any given FNA procedure varies greatly.
Multiple aspirations are usually better than single aspiration of the site. Single aspirate
specimens often contain too few leukocytes for satisfactory analysis.
