Flow Immunophenotyping – What is it and When do you order?

What is it?

Flow immunophenotyping (also known as flow cytometry) is widely used for analyzing the expression of surface and intracellular molecules in order to differentiate and characterize different cell populations.  It continues to be a necessary diagnostic tool for the classification, staging, and monitoring of hematolymphoid neoplasms – mainly acute leukemia and lymphoproliferative disorders such as CLL and other low grade lymphomas.

When should it be ordered?

In a primary care setting, flow immunophenotyping is generally ordered:

1. To investigate persistent, unexplained lymphocytosis.
2. To characterize circulating abnormal lymphocytes or other mononuclear cells (e.g.: blast cells) which could indicate a peripheralized lymphoma or an acute leukemia.  Often flow immunophenotyping will be recommended by the pathologist on the blood film report.  NOTE:  if you suspect your patient has acute leukemia, an urgent hematology/oncology referral is recommended rather than further investigation.  
3. If your patient has a previous diagnosis of acute leukemia and relapse is suspected, flow cytometry can confirm the relapse before referring the patient back to hematology. 
4. Patients who have splenomegaly and/or lymphadenopathy with or without B-symptoms can be screened for lymphoma using flow cytometry.  NOTE:   in such cases the absence of lymphoma cells in the peripheral blood does not exclude a lymphoma diagnosis. 
5. When paroxysmal nocturnal hemogloboinuria (PNH) is suspected.  Although rare, PNH should be considered in patients with unexplained hemolytic anemia.

When should it NOT be ordered?

Patients with a high WBC count due to neutrophilia, eosinophilia, monocytosis, or basophilia should not be investigated using flow immunophenotyping as myeloid leukocytosis is most commonly due to reactive causes. If you suspect a myeloproliferative neoplasm such as CML, a hematology/oncology referral is recommended.
With regard to anemia, flow immunophenotyping should only be used to investigate when there is confirmed, unexplained hemolysis.  This could indicate PNH or an underlying lymphoma.
Flow cytometry is not recommended for investigation of multiple myeloma using peripheral blood.

If you require further information please do not hesitate to contact:

Miranda Wozniak, MD FRCPC
Discipline Head – Hematology
Hematopathologist
Medical-Scientific Department – Ontario
Tel: 416 675 4530 ext. 42040 
miranda.wozniak@lifelabs.com