Value of the use of absolute lymphocyte as surrogate for CD4 count in resource poor situations.

BACKGROUND

The initiation of antiretroviral (ARV) drugs and monitoring of human immunodeficiency virus (HIV) treatment in developing nations such as sub-Sahara Africa is based on the clinical stage and level of CD4 count. Clinical stages can easily be determined using the World Health Organisation (WHO) criteria, this is not so with CD4 count where the right equipment and expertise are not easily available. This lead to various studies being carried out in search of surrogates for CD4 count with use of total lymphocyte count (TLC) being suggested by some studies.

OBJECTIVE

In situation where determination of CD4 cell count is not available or feasible, lymphocyte count is believed to be one alternative method for immunological classification of Acquired Immunodeficiency Syndrome (AIDS). Such assumption may not be true of every population. The objective is, therefore, to examine the correlation between the absolute lymphocyte count and the CD4+ lymphocyte count in HIV positive patients.

MATERIALS AND METHODS

One hundred and sixty-five consecutive HIV positive patients were recruited for the study before the commencement of ARV drugs over a period of 13 months. The haemotological parameters such as the CD4 count was done by flow cytometry using Partec cyflow counter machine made in Germany, with strict adherence to the manufacturer's standard operating procedure. TLC were also determined using Sysmex haematology blood analyser, following the manufacturer's standard operating procedure. Patients were then grouped into CD4 and Total lymphocyte (TLC) categories. These were then compared to determine if there is any correlation as shown in previous studies. Statistical analysis of data was done using Statistical Package for Social Sciences (SPSS) and statistical significance of data was based on P value of less than 0.05. There was significant positive correlation (P value 0.000) between TLC and CD4 count.

RESULTS

Majority of the patients with TLC less than 1000/mm([3]) had CD4 count <200 cells/μl. Using TLC <1000/mm([3]) threshold, there was high sensitivity of 81.8% but low specificity and positive predictive value of 47.5% and 19.4%, respectively, for CD4 count <200 cells/μl. Further assessment using TLC of <1,200/mm([3]) for the currently accepted CD4 count cut-off of <350 cells/μl for initiation of antiretroviral drugs, the sensitivity, specificity, positive predictive value were found to be 76.5%, 26.7%, 21.3%, respectively.

CONCLUSIONS

Considering the low specificity and positive predictive value, it was concluded that the use of TLC of as a surrogate for CD4 count is unreliable. However, where there is no alternative, it could be used with caution bearing in mind its limitations.