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Clinical and Diagnostic Laboratory Immunology, January 2004, p. 29-34, Vol. 11, No. 1
1071-412X/04/$08.00+0 DOI: 10.1128/CDLI.11.1.29-34.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.
Center for International Health, University of Bergen,1 Department of Microbiology and Immunology,3 Department of Internal Medicine, Haukeland University Hospital, Bergen, Norway,4 Centers for Disease Control and Prevention (CDC)Uganda, Global AIDS Program, National Center for HIV, STD and TB, CDC, and Uganda Virus Research Institute, Entebbe, Uganda2
Received 12 August 2003/ Returned for modification 1 October 2003/ Accepted 10 October 2003
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Reference values of hematologic and immunologic indices are necessary for the assessment of health and illness. Aside from their use in routine assessments for anemia, infection, and blood disorders, they are important surrogate markers for assessments of immune status, disease progression, and response to antiretroviral treatment in individuals infected with human immunodeficiency virus (HIV) (16, 18-20). The CD4+-cell count is an essential tool for clinical monitoring of antiretroviral treatment. CD4+-cell counts change dramatically with age, and specific recommendations for the initiation and monitoring of therapy among HIV-positive children have been made on the basis of data from North America and Europe (17). At present, 29.4 million people in sub-Saharan Africa are infected with HIV, and 3 million (10%) of these are children under the age of 15 years (12). As antiretroviral therapy becomes more widely available, it is important that normal reference values for CD4+-cell counts as well as other immunologic and hematologic markers be developed for the African population in order to appropriately manage individuals infected with HIV.
To assess the validity of current reference values of hematologic and immunologic indices for an African population, we collected blood samples from more than 3,000 HIV-negative Ugandans aged 1 week to 92 years.
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Consent. Informed consent was obtained in Luganda, the language commonly spoken locally. Adult participants in the study provided consent for minors younger than age 17 years, in addition to individual assent for participants aged 13 to 17 years. Permission for HIV testing was requested from all participants, and counseling was offered to all consenting participants before the HIV test results were given.
Laboratory. Blood was collected between 9:00 a.m. and 4:00 p.m. by venipuncture, placed in 3-ml Vacutainer tubes (Becton Dickinson, Franklin Lakes, N.J.) containing EDTA, and transported at ambient temperature to the Uganda Virus Research Institute laboratory at Entebbe. Serological tests for HIV were performed by using a standard HIV testing algorithm of two enzyme-linked immunosorbent assays in parallel with Western blotting, as required; reverse transcription-PCR was carried out to confirm the HIV infection status of children younger than age 18 months who were positive by enzyme-linked immunosorbent assay.
A complete blood cell count (CBC) and differential were performed within 12 h of the blood draw by using the Act 5Diff instrument (Beckman Coulter). For determination of CD4+ and CD8+ cell counts, TriTEST reagents (CD3, fluorescein isothiocyanate/CD4, phycoerythrin/CD45, peridinin chlorophyll protein and CD3, fluorescein isothiocyanate/CD8, phycoerythrin/CD45, peridinin chlorophyll protein) were used to stain peripheral blood mononuclear cells according to the protocol of the manufacturer. Blood was stained within 12 h of collection, and the results were analyzed within 24 h. Flow cytometry was performed with a FACScan instrument and MultiSET software (Becton Dickinson) modified to accept manual entry of the total white cell count from the CBC and the percentage of lymphocytes derived from Attractors software (Becton Dickinson), which reports a three-part differential based on cell surface markers and side scatter. By use of this dual-platform approach, the MultiSET software reported the absolute CD3+ CD4+ and CD3+ CD8+ cell counts for the specimen.
Ethics. Study protocols were approved by the Science and Ethics Committee at the Uganda Virus Research Institute, the Uganda National Council for Science and Technology, and the Institutional Review Board at the Centers for Disease Control and Prevention (Atlanta, Ga.).
Statistics. Data were entered into Epi-Info software (version 6; Centers for Disease Control and Prevention) and analyzed by using SAS software (version 9; SAS Institute, Cary, N.C.). The normal distribution was tested by the Kolmogorov-Smirnov test. To investigate the normal distribution of the dependent variables, we plotted the cumulative quantiles for each variable versus the known quantiles of the normal distribution plot (normal Q-Q plots). The sample population was grouped according to the age and gender distribution, and the median was used as a measure of central tendency. The 5th and 95th percentile distributions of the dependent variables were used to specify the 90% reference interval. Kruskal-Wallis nonparametric tests were used to test for differences by age group, and Mann-Whitney U tests were used to test for differences by gender. In the absence of significant differences by gender, the data for all subjects were combined and analyzed as one group. An error probability (P value) of <0.05 was considered significant. Box and whisker plots for lymphocyte subsets were plotted to compare the distribution of this variable across age groups.
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Hematologic indices. The medians and the 5th and 95th percentile reference intervals for the hemoglobin (Hb) level, red blood cell (RBC) count, hematocrit (Hct) level, and mean corpuscular volume (MCV) are presented in Table 1. There were significant differences in hematologic parameters by age and gender; Hb levels, RBC counts, Hct levels, and MCVs increased with age until age 13 years (P < 0.001). Absolute values for Hb levels, RBC counts, Hct levels, and MCVs were significantly higher among male adults than female adults older than age 13 years (P < 0.001). Significant differences by gender were not detected for any of the indices for children younger than 12 years of age.
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TABLE 1. Medians and 90% reference intervals for Hb levels, RBC counts, Hct levels, MCVs, and platelet counts for a Ugandan population, by age group and sex
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WBC counts. Table 2 shows the medians and the 5th and 95th percentile reference intervals for the total white blood cell (WBC), neutrophil, lymphocyte, basophil, and monocyte counts; the counts of all of these cells declined with age. Significant differences among age groups were detected among children younger than age 12 years (P < 0.001). Eosinophil levels markedly increased until 13 years of age and declined thereafter. None of the values for the leukocyte subset showed any differences by gender.
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TABLE 2. Medians and 90% reference intervals for WBC and WBC subset counts for a Ugandan population, by age group
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TABLE 3. Medians and 90% reference intervals for CD4+- and CD8+-cell counts, percentages, and ratios for a Ugandan population, by age group
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FIG. 1. Box and whisker plot showing the median, interquartile, and range CD4+- and CD8+-cell counts (103 cells per milliliter), lymphocyte counts (109 cells per liter), and proportions by age group. The heights of the boxes in the box plots indicate the interquartile lengths. The central bar in each box is the median. Whiskers extend to the most extreme values to 1.5 box lengths from the edge of the box. Circles indicate outliers beyond 1.5 box lengths from the edge of the box. (a) CD4+-cell count by age group; (b) CD4+-cell proportion by age group; (c) CD8+-cell count by age group; (d) CD8+-cell proportion by age group; (e) WBC count by age group; (f) CD4/CD8 ratio by age group.
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TABLE 4. Means and 90% reference intervals for absolute units of WBC and RBC subsets for a Ugandan population compared with standard valuesa
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The low platelet counts and the differences in platelet counts by gender in this population are similar to those detected in other studies with African populations (1, 3, 10, 25). The cause of the low platelet counts among populations of African origin is unknown. While environmental factors and undetected illnesses have been suggested to explain the difference (1, 10), genetic factors may also play a role (3).
The WBC and neutrophil counts in this population are similar to those reported in studies of other African and Afro-Caribbean populations and are lower than standard values (3, 8, 13, 21, 23, 25). The etiology of these differences is unknown, although dietary, environmental, and genetic factors have been proposed (3, 8, 23).
The eosinophil counts found in this study are similar to those reported in other studies from Africa (2, 8, 21, 23). They are consistently higher than those found in Western subjects (27). However, the relative eosinophilia does not appear among African or Afro-Caribbean residents in Europe (3) or among black residents in Cape Peninsula, an urban suburb in South Africa (2), suggesting an environmental rather than a genetic etiology (8). This eosinophilia that was observed may result from a high prevalence of infestations with helminths, particularly schistosomes, in this community resident at the shores of Lake Victoria, predominantly engaged in fishing.
The progressive declines in the absolute values of the total WBC counts and the counts of the CD4+- and CD8+-cell subsets from infancy to adulthood and the higher values for women are similar to other findings (6, 7, 11, 15, 22). An important observation in our study is that the decline in CD4+- and CD8+-cell counts continues throughout childhood until the age of 18 years. European and American studies have shown that the counts for T-cell subsets for children younger than 10 years of age approximate the counts for adults (4, 14, 28, 29). However, a study from neighboring Kenya (6) also found that CD4+- and CD8+-cell counts declined with age until age 10 years, the oldest age group assessed, and that at that age children had not attained the counts detected in adults. Similar to previous reports, women had higher numbers of CD4+ cells and percentages than men in this study. Overall, the population evaluated in this study and that from Kenya (6) tend to have higher CD4+-cell counts and CD4+-cell/CD8+-cell proportions than populations in Europe, North America, and Asia (4, 7, 11), suggesting an ethnic or environmental etiology. The normal range of CD4+-cell counts for the population evaluated in this study is higher than the range of standard Western population-based reference values, which complicates patient management decisions, especially when clinicians must determine the CD4+-cell count or percentage that should be used for HIV-positive children and adults for the initiation of antiretroviral therapy.
The study had several limitations. Despite the large population-based sample, the health status of the individuals was not assessed and no medical or laboratory examinations were performed. In this community, all consenting apparently health individuals found at home at the time of the survey were recruited. The only specific exclusion criterion used was HIV infection. Although none of the participants was moribund at the time of the study, a proportion could have had minor illnesses. This is unlikely to have affected the median values for the population but may have produced proportionately more extreme values. The influences of environmental factors, pregnancy, social habits like smoking, dietary components, and lifestyle were not taken into account, yet there is evidence to suggest that they may be responsible for variations in hematologic parameters (1, 2, 5, 8). Specimen collection was not conducted at exactly the same time of day for all subjects. The temperature and length of blood storage have been shown to cause alterations in the values for some hematologic parameters, and some hematologic parameters have been shown to vary diurnally and day to day, although these differences should have been randomly distributed throughout the study population. All blood samples were shipped at ambient temperature and were processed within 12 h, as recommended for hematologic and immunologic investigations. These findings have been drawn from a preliminary study of 3,048 individuals in a single rural community in Uganda. The very high acceptance rate (94%) for both enrollment in the study and HIV testing allowed the results to be generalizable to the community. However, it would be useful to conduct more expansive studies that include information regarding the time of blood collection and the presence of intercurrent illnesses.
In conclusion, there appear to be regional variations in reference values and ranges of hematologic and immunologic indices between the African population and the population in the industrialized West. These data provide region-specific reference values which can be used to guide patient management and interpretation of clinical research findings and which may potentially improve the quality of clinical care provided to patients.
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