Affordable CD4(+)-T-cell counting by flow cytometry: CD45 gating for volumetric analysis

Assessment of the AQUIOS flow cytometer - An automated sample preparation system for CD4 lymphocyte PanLeucogating enumeration

Background

Flow cytometry has been the approach of choice for enumerating and documenting CD4-cell decline in HIV monitoring. Beckman Coulter has developed a single platform test for CD4+ T-cell lymphocyte count and percentage using PanLeucogating (PLG) technology on the automated AQUIOS flow cytometer (AQUIOS PLG).

Objectives

This study compared the performance of AQUIOS PLG with the Flowcare PLG method and performed a reference interval for comparison with those previously published.

Methods

The study was conducted between November 2014 and March 2015 at 5 different centres located in Canada; Paris, France; Lyon, France; the United States; and South Africa. Two-hundred and forty samples from HIV-positive adult and paediatric patients were used to compare the performances of AQUIOS PLG and Flowcare PLG on a FC500 flow cytometer (Flowcare PLG) in determining CD4+ absolute count and percentage. A reference interval was determined using 155 samples from healthy, non-HIV adults. Workflow was investigated testing 440 samples over 5 days.

Results

Mean absolute and relative count bias between AQUIOS PLG and Flowcare PLG was −41 cells/µL and −7.8%. Upward and downward misclassification at various CD4 thresholds was ≤ 2.4% and ≤ 11.1%. The 95% reference interval (2.5th – 97.5th) for the CD4+ count was 453–1534 cells/µL and the percentage was 30.5% – 63.4%. The workflow showed an average number of HIV samples tested as 17.5 per hour or 122.5 per 8-hour shift for one technician, including passing quality controls.

Conclusion

The AQUIOS PLG merges desirable aspects from conventional flow cytometer systems (high throughput, precision and accuracy, external quality assessment compatibility) with low technical operating skill requirements for automated, single platform systems.

Shifting the HIV Paradigm from Care to Cure: Proceedings from the Caribbean Expert Summit in Barbados, August 2017

The CCAS EXPERT SUMMIT convened an array of international experts in Barbados on August 27-31, 2017 under the theme "From Care to Cure-Shifting the HIV Paradigm." The Caribbean Cytometry & Analytical Society (CCAS) partnered with the Joint United Nations Programme on HIV/AIDS (UNAIDS) to deliver a program that reviewed the advances in antiretroviral therapy and the public health benefits accruing from treatment as prevention. Particular emphasis was placed on reexamining stigma and discrimination through a critical appraisal of whether public health messaging and advocacy had kept pace with the advances in medicine. Persistent fear of HIV driving discriminatory behavior was widely reported in different regions and sectors, including the healthcare profession itself; continued fear of the disease was starkly misaligned with the successes of new medical treatments and progress toward the UNAIDS 90-90-90 targets. The summit therefore adopted the mantra "Test-Treat-Defeat" to help engage with the public in a spirit of optimism aimed at creating a more conducive environment for persons to be tested and treated and, thereby, help reduce HIV disease and stigma at the individual and community levels.

Performance verification of the new fully automated Aquios flow cytometer PanLeucogate (PLG) platform for CD4-T-lymphocyte enumeration in South Africa

BACKGROUND

The National Health Laboratory Service (NHLS) offers wide-scale CD4 testing through a network of laboratories in South Africa. A new "load and go" cytometer (Aquios CL, Beckman Coulter), developed with a PLG protocol, was validated against the predicate PLG method on the Beckman Coulter FC500 MPL/CellMek platform.

METHODS

Remnant routine EDTA blood CD4 reference results were compared to results from two Aquios/PLG instruments (n = 205) and a further n = 1885 samples tested to assess daily testing capacity. Reproducibility was assessed using ImmunotrolTM and patient samples with low, medium, high CD4 counts. Data was analyzed using GraphPad software for general statistics and Bland-Altman (BA) analyses. The percentage similarity (%Sim) was used to measure the level of agreement (accuracy) of the new platform versus the predicate and variance (%SimCV) reported to indicate precision of difference to predicate.

RESULTS

205 samples were tested with a CD4 count range of 2-1228 cells/μl (median 365cells/μl). BA analysis revealed an overall -40.5±44.0cells/μl bias (LOA of 126.8 to 45.8cells/μl) and %Sim showing good agreement and tight precision to predicate results (94.83±5.39% with %SimCV = 5.69%). Workflow analysis (n = 1885) showed similar outcomes 94.9±8.9% (CV of 9.4%) and 120 samples/day capacity. Excellent intra-instrument reproducibility was noted (%Sim 98.7±2.8% and %SimCV of 2.8%). 5-day reproducibility using internal quality control material (Immunotrol™) showed tight precision (reported %CV of 4.69 and 7.62 for Normal and Low material respectively) and instrument stability.

CONCLUSION

The Aquios/PLG CD4 testing platform showed clinically acceptable result reporting to existing predicate results, with good system stability and reproducibility with a slight negative but precise bias. This system can replace the faded XL cytometers in low- to medium volume CD4 testing laboratories, using the standardized testing protocol, with better staff utilization especially where technical skills are lacking. Central monitoring of on-board quality assessment data facilitates proactive maintenance and networked instrument performance monitoring.

Age- and sex-related reference intervals of lymphocyte subsets in healthy ethnic Han Chinese children

Immunophenotyping of blood lymphocytes has become an important tool in the diagnosis of immunologic and hematologic disorders such as immunodeficiencies, lymphoproliferative and autoimmune diseases. Lymphocyte subsets include total T-cells (CD3(+)), TH (T helper, CD3(+) CD4(+)), TC (cytotoxic T cells, CD3(+) CD8(+)), B-cells (CD3(-) CD19(+)), and NK-cells (CD3(-) CD16(+) CD56(+)). Specific lymphocyte subset reference intervals should be locally established for meaningful comparison and to obtain an accurate interpretation of the results. Reference intervals of lymphocyte subsets for Chinese children are scarce. We performed dual-platform flow cytometry to determine the reference intervals of the percentages and absolute counts of lymphocyte subsets, including total T-cells, TH cells, TC cells, B-cells, and NK-cells in 1,027 ethnic Han children aged 4 months to 7 years in Henan, China. The children were divided into seven age groups. The percentages and absolute counts differed significantly with age, with the percentages of TH cells and B cells and the CD4/CD8 ratio peaking during the first year, while the percentages of total T cells, TC cells, and NK cells were obviously increased with age; girls showed a trend toward having a higher percentage of TH cells and a higher CD4/CD8 ratio than boys. The absolute counts of lymphocyte subsets peaked during first year and then decreased steadily with age. The reference intervals of lymphocyte subsets among children from China differed from the reported values in Hong Kong, the United States, Cameroon, and Italy. The differences observed could be due to genetic and environmental factors, coupled with the methodology used. The reference intervals of lymphocyte subsets could be used as initial national reference ranges in guidelines for children aged 4 months to 7 years.

Quantification of cells with specific phenotypes I: determination of CD4+ cell count per microliter in reconstituted lyophilized human PBMC prelabeled with anti-CD4 FITC antibody

A surface-labeled lyophilized lymphocyte (sLL) preparation has been developed using human peripheral blood mononuclear cells prelabeled with a fluorescein isothiocyanate conjugated anti-CD4 monoclonal antibody. The sLL preparation is intended to be used as a reference material for CD4+ cell counting including the development of higher order reference measurement procedures and has been evaluated in the pilot study CCQM-P102. This study was conducted across 16 laboratories from eight countries to assess the ability of participants to quantify the CD4+ cell count of this reference material and to document cross-laboratory variability plus associated measurement uncertainties. Twelve different flow cytometer platforms were evaluated using a standard protocol that included calibration beads used to obtain quantitative measurements of CD4+ T cell counts. There was good overall cross-platform and counting method agreement with a grand mean of the laboratory calculated means of (301.7 ± 4.9) μL(-1) CD4+ cells. Excluding outliers, greater than 90% of participant data agreed within ±15%. A major contribution to variation of sLL CD4+ cell counts was tube to tube variation of the calibration beads, amounting to an uncertainty of 3.6%. Variation due to preparative steps equated to an uncertainty of 2.6%. There was no reduction in variability when data files were centrally reanalyzed. Remaining variation was attributed to instrument specific differences. CD4+ cell counts obtained in CCQM-P102 are in excellent agreement and show the robustness of both the measurements and the data analysis and hence the suitability of sLL as a reference material for interlaboratory comparisons and external quality assessment.

Field evaluation in Chad of community usage of CD4 T lymphocyte counting by alternative single-platform flow cytometry

Background

Field and community evaluation of the routine usage of CD4 T counting platforms is essential in resource-poor countries for efficient and cost-effective monitoring of HIV-infected adults and children attending health care centers.

Methods

We herein addressed the principal issues raised by the implementation of the single-platform, volumetric Auto40 flow cytometer (Apogee Flow Systems Ltd, Hemel Hempstead, UK) in 8 community HIV monitoring laboratories of different levels throughout Chad. This is a country with particularly difficult conditions, both in terms of climate and vast geographical territory, making the decentralization of the therapeutic management of HIV-infected patients challenging.

Results

The routine usage of the Auto40 flow cytometers for a period of 5 years (2008–2013) confirms the reliability and robustness of the analyzer for community-based CD4 T cell enumeration in terms of both absolute numbers and percentages to enable accurate monitoring of HIV-infected adults and children. However, our observations suggest that the Auto40 mini flow cytometer is not suitable for all laboratories as it is oversized and ultimately very expensive.

Conclusion

The Chad experience with the Auto40 flow cytometer suggests that its usage in resource-limited settings should be mainly reserved to reference (level 1) or district (level 2) laboratories, rather than to laboratories of health care centres (level 3).

Comparison of two methodologies for CD4⁺ T lymphocytes relative counting on immune monitoring of patients with human immunodeficiency virus

Considering that counting the percentage of CD4 T lymphocytes can add prognostic information regarding patients infected with HIV, the aim of this study was to evaluate the percentage values of CD4+ T lymphocytes from 81 patients determined by flow cytometry and estimated by flow cytometry in conjunction with a hematology counter. Means were compared through the Student's t-test. Pearson's correlation was determined, and the agreement between results was tested by Bland-Altman. The level of significance was P < 0.05. It was found a significantly higher mean difference between the relative values of CD4+ T lymphocytes to the hematologic counter (P < 0.05), for all strata studied. Positive and significant correlations (P < 0.01) were found between the strata CD4 < 200 cells/mL (r = 0.93), between 200 and 500 cells/mL (r = 0.65), and >500 cells/mL (r = 0.81). The limits of agreement were 1.0 ± 3.8% for the stratum of CD4 < 200 cells/mL, approximately 2.2 ± 13.5% for the stratum of CD4 between 200 and 500 cells/mL, and approximately 6.2 ± 20.4% for the stratum > 500 cells/mL. The differences in the percentages of CD4+ T lymphocytes obtained by different methodologies could lead to conflict when used in clinical decisions related to the treatment and care of people infected with HIV.

Validation of a single-platform, volumetric, CD45-assisted PanLeucogating Auto40 flow cytometer to determine the absolute number and percentages of CD4 T cells in resource-constrained settings using Cameroonian patients' samples

The study evaluated the single-platform, volumetric, CD45-assisted PanLeucogating Auto40 flow cytometer (Apogee Flow Systems Ltd., Hemel Hempstead, United Kingdom) for CD4 T cell numeration, compared to the reference FACSCalibur flow cytometer. Results of absolute counts and percentages of CD4 T cells by Auto40 and FACSCalibur of 234 tripotassium EDTA (K3-EDTA)-blood samples from 146 adults and 88 children (aged from 18 months to 5 years), living in Yaoundé, Cameroon, were highly correlated (r(2) = 0.97 and r(2) = 0.98, respectively). The mean absolute bias and relative bias between Apogee Auto40 and FACSCalibur absolute CD4 T cell counts were +9.6 cells/μl, with limits of agreement from -251 to 270 cells/μl, and +4.1%, with limits of agreement from -16.1 to 24.4%, respectively. The mean absolute bias and relative bias between Apogee Auto40 and FACSCalibur CD4 T cell results expressed as percentages were +0.05% CD4 (95% confidence interval [CI], -0.03 to 0.41), with limits of agreement from -6.0 to 5.9% CD4, and +1.0%, with limits of agreement from -32.3 to 34.4%, respectively. The Auto40 counting allowed identification of the majority of adults with CD4 T cell counts below 200 cells/μl (sensitivity, 87%; specificity, 98%) or below 350 cells/μl (sensitivity, 92%; specificity, 98%) and of children with CD4 T cell counts below 750 cells/μl (sensitivity, 82%; specificity, 98%) or below 25% CD4(+) (sensitivity, 96%; specificity, 99%). The Auto40 analyzer is a reliable alternative flow cytometer for CD4 T lymphocyte enumeration to be used in routine immunological monitoring according to the WHO recommendations for HIV-infected adults as well as children living in resource-constrained settings.

Immunohaematological reference values in human immunodeficiency virus-negative adolescent and adults in rural northern Tanzania

Background

The amount of CD4 T cells is used for monitoring HIV progression and improvement, and to make decisions to start antiretroviral therapy and prophylactic drugs for opportunistic infections. The aim of this study was to determine normal reference values for CD4 T cells, lymphocytes, leucocytes and haemoglobin level in healthy, HIV negative adolescents and adults in rural northern Tanzania.

Methods

A cross sectional study was conducted from September 2006 to March 2007 in rural northern Tanzania. Participants were recruited from voluntary HIV counselling and testing clinics. Patients were counselled for HIV test and those who consented were tested for HIV. Clinical screening was done, and blood samples were collected for CD4 T cell counts and complete blood cell counts.

Results

We enrolled 102 participants, forty two (41.2%) males and 60 (58.8%) females. The mean age was 32.6 ± 95% CI 30.2–35.0. The mean absolute CD4 T cell count was 745.8 ± 95% CI 695.5–796.3, absolute CD8 T cells 504.6 ± 95% CI 461.7–547.5, absolute leukocyte count 5.1 ± 95% CI 4.8–5.4, absolute lymphocyte count 1.8 ± 95% CI 1.7–1.9, and haemoglobin level 13.2 ± 95% CI 12.7–13.7. Females had significantly higher mean absolute CD4 T cell count (p = 0.008), mean absolute CD8 T cell count (p = 0.009) and significantly lower mean haemoglobin level than males (p = 0.003)

Conclusion

Immunohaematological values found in this study were different from standard values for western countries. Females had significantly higher mean CD4 T cell counts and lower mean haemoglobin levels than males. This raises the issue of the appropriateness of the present reference values and guidelines for monitoring HIV/AIDS patients in Tanzania.

Evaluation of a simplified dual-platform flow cytometric method for measurement of lymphocyte subsets and T-cell maturation phenotypes in the population of Nouna, Burkina Faso

In the context of a larger clinical study in Nouna, Burkina Faso, we evaluated a simplified dual-platform (DP) flow cytometric (FCM) method that allows the determination of major lymphocyte subsets in a single test tube. We compared the phenotyping of lymphocytes with DP FCM and simultaneous measurements with standard single-platform (SP) FCM for samples from 177 individuals. Analysis of the comparative measurements revealed that DP FCM systematically underestimates the proportion of NK cells, overestimates the percentage of CD3(+) CD8(+) lymphocytes, and yields proportions of B cells and CD4(+) T cells comparable with the results from SP FCM. Bland-Altman analysis showed a low bias between both methods and an acceptable precision for percent values of CD4(+) T cells (bias +/- precision, -1% +/- 6%) and CD8(+) T cells (-3% +/- 6%). The absolute cell numbers of all lymphocyte subpopulations, however, were systematically biased towards lower values being obtained by DP FCM. Reference values for the distribution of T-cell maturation phenotypes in 177 healthy adults were calculated using DP FCM. The mean +/- standard deviation (SD) CD4(+)-to-CD8(+) T-cell ratio was 1.61 +/- 0.61, the mean percentage +/- SD of CD4(+) T cells was 42% +/- 7%, and that of CD8(+) T cells 29% +/- 7%. Among CD4(+) lymphocytes, 28% +/- 7% were classified as central memory (CD45RA(low) CCR7(+)), 22% +/- 10% as naïve (CD45RA(high) CCR7(+)), 45% +/- 12% as effector memory (CD45RA(low) CCR7(-)); and 5% +/- 3% as terminally differentiated effector memory expressing CD45RA (CD45RA(high) CCR7(-)). Among CD8(bright) lymphocytes, 3% +/- 2% had a central memory phenotype, 27% +/- 13% were naïve, 37% +/- 13% had an effector memory phenotype, and 34% +/- 12% were terminally differentiated effector memory cells expressing CD45RA.

Comparison of capillary based microflurometric assay for CD4+ T cell count estimation with dual platform Flow cytometry

The CD4+ T cell count estimation is an important monitoring tool for HIV disease progression and efficacy of anti-retroviral treatment (ART). Due to availability of ART at low cost in developing countries, quest for reliable cost effective alternative methods for CD4+ T cell count estimation has gained importance. A simple capillary-based microflurometric assay (EasyCD4 System, Guava Technology) was compared with the conventional flow cytometric assay for estimation of CD4+ T cell counts in 79 HIV infected individuals. CD4+ T cell count estimation by both the assays showed strong correlation (r = 0.938, p < 0.001, 95% CI 0.90 to 0.96). The Bland Altman plot analysis showed that the limits of variation were within agreeable limits of ± 2SD (-161 to 129 cells/mm³). The Easy CD4 assay showed 100% sensitivity for estimating the CD4+ T cell counts < 200 cells/mm³ and < 350 cells/mm³ and 97% sensitivity to estimate CD4+ T cell count < 500 cells/mm³. The specificity ranged from 82 to 100%. The Kappa factor ranged from 0.735 for the CD4+ T cell counts < 350 cells/mm³ to 0.771 for < 500 cells/mm³ CD4+ T cell counts. The system works with a simple protocol, is easy to maintain and has low running cost. The system is compact and generates minimum amount of waste. Hence the EasyCD4 System could be applied for estimation of CD4+ T cell counts in resource poor settings.

Evaluation of a new single-parameter volumetric flow cytometer (CyFlow(green)) for enumeration of absolute CD4+ T lymphocytes in human immunodeficiency virus type 1-infected Thai patients

Use of the standard dual-platform flow cytometric method for determination of CD4(+) T-lymphocyte counts, which needs both a flow cytometer (FCM) and hematological analyzer, would inevitably lead to increased variability. The development of new single-platform (SP) FCMs that provide direct CD4(+) T-lymphocyte counts for improved assay precision and accuracy have recently attracted attention. This study evaluated one of those systems, CyFlow(green) (Partec), a single-parameter SP volumetric FCM. The performance of CyFlow(green) was compared with those of two reference standard SP microbead-based technologies of the three-color TruCOUNT tube with the FACScan FCM and a two-color FACSCount system (Becton Dickinson Biosciences). Absolute CD4(+) and CD8(+) T-lymphocyte counts in 200 human immunodeficiency virus type 1-seropositive blood specimens were determined. Statistical analysis for correlation and agreement were performed. A high correlation of absolute CD4 counts was shown when those obtained with CyFlow(green) were compared with those obtained with the bead-based three-color TruCOUNT system (R(2)=0.96; mean bias, -69.1 cells/microl; 95% confidence interval [CI], -225.7 to+87.5 cells/microl) and the FACSCount system (R(2)=0.97; mean bias, -40.0 cells/microl; 95% CI, -165.1 to+85.1 cells/microl). The correlation of the CD4(+) T-lymphocyte counts obtained by the two bead-based systems was high (R(2)=0.98). Interestingly, CyFlow(green) yielded CD4(+) T-lymphocyte counts that were 21.8 and 7.2 cells/microl lower than those obtained with the TruCOUNT and the FACSCount systems, respectively, when CD4(+) T-lymphocyte counts were <250 CD4(+) T-lymphocyte counts/microl range or 17.3 and 5.8 cells/microl less, respectively, when CD4(+) T-lymphocyte counts were <200 cells/microl. The single-parameter CyFlow(green) volumetric technology performed well in comparison with the performance of the standard SP bead-based FCM system. However, a multicenter comparative study is needed before this FCM machine is implemented in resource-limited settings.

CD4 measurements in patients with HIV: are they feasible for poor settings?

The lack of facilities to measure CD4 counts in poor countries impedes instituting rational and effective antiretroviral therapy in these countries. Can a new microchip counting technique help to solve the problem?

A microchip CD4 counting method for HIV monitoring in resource-poor settings

BACKGROUND

More than 35 million people in developing countries are living with HIV infection. An enormous global effort is now underway to bring antiretroviral treatment to at least 3 million of those infected. While drug prices have dropped considerably, the cost and technical complexity of laboratory tests essential for the management of HIV disease, such as CD4 cell counts, remain prohibitive. New, simple, and affordable methods for measuring CD4 cells that can be implemented in resource-scarce settings are urgently needed.

METHODS AND FINDINGS

Here we describe the development of a prototype for a simple, rapid, and affordable method for counting CD4 lymphocytes. Microliter volumes of blood without further sample preparation are stained with fluorescent antibodies, captured on a membrane within a miniaturized flow cell and imaged through microscope optics with the type of charge-coupled device developed for digital camera technology. An associated computer algorithm converts the raw digital image into absolute CD4 counts and CD4 percentages in real time. The accuracy of this prototype system was validated through testing in the United States and Botswana, and showed close agreement with standard flow cytometry (r = 0.95) over a range of absolute CD4 counts, and the ability to discriminate clinically relevant CD4 count thresholds with high sensitivity and specificity.

CONCLUSION

Advances in the adaptation of new technologies to biomedical detection systems, such as the one described here, promise to make complex diagnostics for HIV and other infectious diseases a practical global reality.

Comparison of a new, affordable flow cytometric method and the manual magnetic bead technique for CD4 T-lymphocyte counting in a northern Nigerian setting

We compared two techniques for CD4 T-lymphocyte counting: flow cytometry (Cyflow) and magnetic beads (Dynabead). Similar results with good correlation were obtained from the 40 adult blood samples counted (P=0.057, r=0.93). The Cyflow technique is more precise and cost-effective than the Dynabead method ($3 to $5 versus $12 to $22 per test, respectively), since as many as 200 samples can be measured per day.

Low CD4+ T-lymphocyte values in human immunodeficiency virus-negative adults in Botswana

CD4+-lymphocyte counts (LCs) play a crucial role in the management and monitoring of HIV infection. Variability in CD4+ LCs has been reported to occur as a result of measurement techniques and/or biological variations. We report on the CD4+ LCs of healthy human immunodeficiency virus (HIV)-seronegative adults in Botswana. Samples were obtained from HIV-seronegative blood donors. The median CD4+ LC was 726 cells/mm3 (for females, 782 cells/mm3; for males, 698 cells/mm3). The median CD8+ LC was 488 cells/mm3 (for females, 494 cells/mm3; for males, 485 cells/mm3). The median CD4+-to-CD8+ ratio was 1.57 (for females, 1.66; for males, 1.51). Our findings of low CD4+ LCs among HIV-negative adults in Botswana are significant and have important implications for the management of HIV disease in the population of this sub-Saharan African country.

HIV/AIDS in Central Africa: pathogenesis, immunological and medical issues

The estimated worldwide prevalence of human immunodeficiency virus (HIV) infections topped 52.5 million in June 2003, a mere 20 years after the aetiological agent was shown to be a sexually transmissible virus with a predilection for CD4+ T lymphocytes. More than 22 million people have died of the acquired immunodeficiency syndrome (AIDS) and the condition has in one generation become the most devastating and persistent epidemics in recorded history. More than two thirds of the world total of HIV-infected people live in Sub-Saharan Africa. In Central and Southern Africa at least 20% of the adult population is infected. As these adults die, they leave increasing numbers of orphans. Life expectancy at birth declined by 10 years per decade since the late 1980s to 50 years in the late 1990s, and in Botswana it is estimated to be as low as 33 years by 2010. The epidemic is increasing unabated and prospects for a curative or protective vaccine remain remote. The impact on HIV in Africa has been so profound that it influences political, economic, agriculture/food security, social, education, defence, science and health considerations. The medical and in particular immunology communities in Central Africa have the invidious challenge of on the one hand diagnosing the condition, monitoring its impact and contributing to treatment and management efforts. The science and clinical practice of immunology is challenged to find answers to the epidemic, perhaps including a vaccine. In this review we address the peculiarities of the HIV epidemic in Africa, its epidemiology and immunopathogenesis. We address the effect of the epidemic on individual patients, in their homes, workplaces and the knock-on effects on families and friends of the infected. Respective specialists discuss special groups (women, children) that are predominantly seen in Africa. We also discuss the impact of the epidemic on the clinical practice of medicine in general and challenges faced in the introduction of antiretroviral medicines. We also discuss options available for the diagnosis, treatment and monitoring of HIV-infected patients in this region.

Use of total lymphocyte count for monitoring response to antiretroviral therapy

The CD4 cell count has become a key laboratory measurement in the management of human immunodeficiency virus (HIV) disease. In ideal situations, HIV-infected persons are followed up longitudinally with serial CD4 cell counts to determine disease progression, risk for opportunistic infection, and the need for prophylactic or therapeutic intervention. However, the use of the CD4 cell count in resource-limited settings is often not possible because of lack of availability and high cost. Thus, other laboratory markers have been proposed as substitutes for the CD4 cell count. The data regarding the clinical utility of the total lymphocyte count (TLC) as a potential surrogate marker of immune function in patients with HIV disease are examined. The role of the TLC in the initiation of antiretroviral therapy and opportunistic infection prophylaxis, as well as the role of the TLC in monitoring the response to antiretroviral therapy, are also addressed.