A TLC of 1,200 cells/mL or less has been used as a surrogate for a CD4 cell count of 200 cells/microliters or less in settings where resources are limited and there is no ability to measure CD4 cell count. However, some studies have shown that TLC-based estimates can have a poor correlation with actual CD4 cell count.

Dr. Ray Y. Chen and colleagues at the University of Alabama at Birmingham (UAB) and elsewhere developed a decision tree based on multiple components of the CBC -- including TLC, hemoglobin and platelet count -- and adjusted for gender, body mass index (BMI) and antiretroviral therapy status.

The algorithm was developed from complete blood counts obtained from 1,189 patients attending the UAB Outpatient HIV Clinic since 1994. Results were compared with blood samples from Zambia and the Birmingham Veterans Affairs Medical Center.

Dr. Chen and colleagues report that the "UAB-based decision tree performed better than the TLC cutpoint of 1,200 cells/mL" in the BVAMC and Zambian samples.

The investigators caution that "a given model is not always applicable in another population." They say additional studies may show that "the best model to identify a low CD4 cell count may be one based on local data."

This or a similar model provides a reliable, affordable method of estimating CD4 cell counts in HIV-infected patients in resource-limited areas, the team concludes.

J Acquir Immune Defic Syndr 2007;44:525-530.

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