By John Otrompke
CHICAGO -- November 4, 2009 -- Flow cytometry analysis by CD45/side-scatter histogram is enough to confirm an initial finding of low CD3 cell count without recourse to confirmation by lymphosum tube analysis, according to a study presented at the American Society for Clinical Pathology (ASCP) 2009 Annual Meeting.
The study attempted to clarify the recommendation of the US Centers for Disease Control and Prevention.
"In our study, if the CD3 percentage was <60%, we repeated the test with the lymphosum tube," said Kim Le, Central Laboratory, Intermountain Healthcare, Murray, Utah, on October 30.
"The CDC did not give out a number in their recommendation; they said that if we have questions about the finding, we should use the lymphosum tube method to confirm our results and that it is up to the lab to determine what is right."
In the first test pathologists count cells by assessing side scatter. "We can detect the complexity of the cell, because if the cell is smaller or more complex, it has a lower side scatter," Le said. They are also able to count CD45 cells, which test positive for leukocytes. Such cells appear bright on the test, he said.
In using the follow-up test recommended by the CDC for uncertain cases, pathologists use a lymphosum tube containing CD3, CD16 (natural killer cell), and CD19.
"To make sure we did not gauge the test result on the wrong cell population, we have all the cells accounted for by using the lymphosum tube," Le explained.
However, the study found that repeating the test when the CD3 percentage was <60% is unnecessary.
From December 2006 to January 2009, a 4-colour monoclonal panel was used to evaluate 1,433 whole-blood samples from immunocompromised patients for percentage and absolute count of CD3, CD4, and CD8. If the CD3 percentage was <60% and the patient had not had a similar low result, a second reflex tube containing CD3, CD16, CD19, and CD45 was set up for lymphosum evaluation. High purity and recovery of the lymphoid population is indicated by a lymphosum of 90% to 110%.
A CD3 percentage between 19% and 59% was found in 106 specimens. Because the lymphosum of most of the samples was 90% to 105%, the researchers determined that use of the lymphosum tube was unnecessary.
"Our results indicate that using CD45 and side scatter should be good enough," clarified Le, adding, "This is only for the patient previously diagnosed with HIV. For these patients, CD3 counts are used for staging of the disease, not for the purpose of diagnosis."
[Presentation title: Determining the Utility of the Lymphosum in CD4 Evaluations. Abstract 37]
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