Epidemiology of Anemia in Human Immunodeficiency Virus (HIV)-Infected Persons: Results From the Multistate Adult and Adolescent Spectrum of HIV Disease Surveillance Project

ANEMIA IS A FREQUENT complication of infection with the human immunodeficiency virus type 1 (HIV-1) and may have multiple causes.1 In different study settings, the prevalence of anemia in persons with acquired immunodeficiency syndrome (AIDS) has been estimated at 63% to 95%,2-5 making it more common than thrombocytopenia or leukopenia in patients with AIDS.3 6 This high prevalence of anemia may be because of a high incidence of anemia, a long duration of anemia, or a combination of both.

HIV infection may lead to anemia in many ways: changes in cytokine production with subsequent effects on hematopoiesis^7-9; decreased erythropoietin concentrations^10,11; opportunistic infectious agents, such as Mycobacterium aviumcomplex12 and parvovirus B-19¹³; administration of chemotherapeutic agents such as zidovudine,14 ganciclovir,15 and trimethoprim-sulfamethoxazole¹⁶; and myelophthisis caused by cancers such as lymphosarcoma. Other mechanisms for HIV-associated anemia, although uncommon, include vitamin B₁₂deficiency17 and the autoimmune destruction of red blood cells.18 Direct infection of marrow precursor cells19 has been hypothesized, but not proven.

Anemia has been associated with progression to AIDS20 and shorter survival times21,22 for HIV-infected patients. No published data have shown whether, given that anemia has developed, recovery from anemia is associated with improved survival. Understanding the association between anemia and survival is important because treatments for anemia are available including recombinant human erythropoietin (r-huEPO),23 blood transfusion, and, in drug-induced anemia, cessation of myelosuppressive therapies.

To study the occurrence, associations, and effect of anemia on the survival of HIV-infected patients, we analyzed data from the medical records of 32,867 persons enrolled in a project that provided surveillance for opportunistic illnesses, other clinical conditions, drugs prescribed, and laboratory data for persons infected with HIV.

We analyzed data from January 1990 (when the project began) through August 1996 from the records of patients in the Adult and Adolescent Spectrum of HIV Disease Surveillance Project, a multicenter medical record review in nine United States cities.24 Each project site developed procedures to ensure patient confidentiality and conducted the project according to guidelines of local human subjects review committees. Depending on the project site, either all patients infected with HIV who attended participating clinics or a systematic sample of patients who attended were eligible for observation, and HIV-infected patients with and without AIDS were observed. A standardized instrument was used to collect information on the patient's clinical conditions, laboratory values, and treatments during the year preceding the first medical record abstraction (baseline review); similar information was collected by medical record review every 6 months until the patient's death or last contact (semester abstractions). For each semester abstraction, we used the most recent hemoglobin determination in the semester.

Prevalent hemoglobin concentration was defined as the first recorded hemoglobin concentration recorded after first observation in Adult and Adolescent Spectrum of HIV Disease Project (ASD). Univariate statistics were calculated on prevalent hemoglobin concentrations stratified by sex. Strata of hemoglobin concentrations were created based on sex-specific reference ranges.25 For men strata were <10, 10 to 14, and ≥14 g/dL; for women strata were <10, 10 to 12, and ≥12 g/dL. Stratified hemoglobin concentrations are presented by stage of HIV disease.

For all other analyses, anemia was defined as a hemoglobin concentration of less than 10 g/dL or an International Classification of Diseases (ICD-9) diagnosis code of 280 to 281.99 (iron deficiency anemia and other deficiency anemias), 283 to 284.79 (acquired hemolytic anemias), 648.2 to 648.29 (anemia complicating pregnancy or childbirth), or 284.9 to 285.99 (aplastic anemia, other than drug related, and other unspecified anemias). Drug-related anemia was defined as a diagnosis of anemia for which the physician specified a drug-related cause in the medical record or for which an ICD-9 code of 284.8 (aplastic anemia caused by drugs) was recorded; all other diagnoses were considered unrelated to drugs.

To determine whether a person with anemia recovered from anemia, hemoglobin levels measured during two semesters after the semester of anemia diagnosis (or one semester, if there was only one semester of follow-up) were compared with the level from the semester of anemia diagnosis. If both hemoglobin levels determined after anemia diagnosis were more than 10.0 g/dL and were at least 1.0 g/dL more than the level at the time of anemia diagnosis, the person was considered to have recovered.

To calculate the incidence of anemia, all anemia diagnoses in the 1-year period from 6 months to 18 months after baseline review (semesters 2 and 3, defined as the study year) were counted; the analysis included all patients who were observed through the end of the study year, died during the study year, or had anemia during the study year. Patients who had only one semester of follow-up, prevalent anemia (defined as anemia during the semester before the study year), or no CD4 count or hemoglobin level during the study year were excluded (Table 1). Multiple logistic regression was performed to describe the associations of demographic variables (sex, age < or ≥45 years, race, and HIV exposure mode), stage of disease (CD4 T-lymphocyte count of < or ≥ 200 cells/μL, and diagnosis of any AIDS-defining opportunistic illness), illnesses (bacterial septicemia, lymphoma, andMycobacterium avium complex), laboratory data (neutropenia and thrombocytopenia), and chemotherapeutic agents (zidovudine, didanosine, dideoxycytidine, trimethoprim-sulfamethoxazole, ganciclovir, and fluconazole) with the occurrence of anemia during the study year. Drug prescriptions during the semester preceding the semester of anemia incidence, and clinical conditions present during the semester of anemia incidence were examined. Because of the large numbers of observations available, all covariates were kept in the regression model regardless of statistical significance. Separate regression models were constructed for the outcomes of anemia related to drugs and anemia unrelated to drugs. For persons who did not develop anemia, semester 2 was considered the referent semester to determine covariates. The results are reported as adjusted odds ratios (AORs), with 99% confidence intervals (CIs). We used 99% CIs because we performed a large number of tests of significance.

Analyses of mortality were conducted from the first CD4 T-lymphocyte count after baseline review (“first CD4 count”) to the date of death, last contact, or loss to follow-up. For 75% of patients, the first CD4 count was done in the first semester after baseline review; for 90%, the first CD4 count was done in the first two semesters after baseline review. Patients were excluded if they (1) did not have a blood hemoglobin level and CD4 count at any time after baseline review, (2) developed anemia before the first CD4 count, or (3) had no follow-up after the date of the first CD4 count (Table 2).

The Kaplan-Meier method was used to describe the median survival of patients after the first CD4 count, and the log rank test was used to determine differences in survival between those persons who had (1) no anemia, (2) drug-related anemia, or (3) anemia unrelated to drugs. Proportional hazards regression was conducted to evaluate the effect of anemia on survival from the first CD4 count. The time-dependent regressors were clinical AIDS, antiretroviral therapy (at least one therapy of zidovudine [ZDV], didanosine, or dideoxycytidine),Pneumocystis carinii pneumonia prophylaxis (at least one therapy of aerosolized pentamidine, trimethoprim-sulfamethoxazole [TMP-SMX], or dapsone), neutropenia (white blood cell count of <2,500/μL), thrombocytopenia (platelet count of <50,000/μL or physician diagnosis), and anemia. Non-time–dependent regressors were sex, age (<25, 25 to 44, or ≥45 years), and HIV exposure mode. Separate analyses were conducted for subgroups stratified by first CD4 counts. The results of these analyses are reported as risk ratios with 99% CIs.

In analyses to describe the effects of recovery from anemia on mortality, patients were excluded if they (1) did not have a diagnosis of anemia after first CD4 count, (2) did not have at least one measurement of hemoglobin level in a semester after the incident semester, or (3) had no follow-up after the date of the first CD4 count. The Kaplan-Meier method and proportional hazards regression were conducted as already described to determine the effect of recovery from anemia on mortality after the first CD4 count. Separate analyses were conducted for subgroups stratified by first CD4 counts. The results of these analyses are reported as median survival of patients after first CD4 count and as risk ratios with 99% CIs.

Data from the medical records of 32,867 patients were analyzed. Of these, 31,534 (96%) had at least one hemoglobin concentration abstracted. The distribution of the first abstracted value (prevalent concentration) is shown in Table 3. The distribution of hemoglobin strata varied dramatically with stage of HIV disease: For HIV-infected persons with no AIDS, 72% and 69% of men and women, respectively, had hemoglobin concentrations within the reference range (greater than 14 or 12 g/dL, respectively). However, for persons with clinical AIDS, only 13% and 23% of men and women, respectively, had hemoglobin concentrations within the reference range.

A total of 13,315 had sufficient follow-up time and all information required for analysis of incidence; the characteristics of persons who were included and those who were excluded were similar (Table 1). Incidence of anemia was associated with clinical stage of disease: 1-year incidence was 3.2% for 6,094 persons with HIV infection but not AIDS, 12.1% for 2,579 persons with immunologic AIDS (CD4 of <200/μL or CD4 percentage of <14), but not clinical AIDS, and 36.9% for 4,642 persons with clinical AIDS. In all groups there were 2,222 anemia diagnoses, of which 494 (22.2%) were drug related. Most diagnoses (1,311, 59%) were based only on low hemoglobin level; 505 diagnoses (23%) were based only on ICD-9 codes and 406 diagnoses (18%) were based both on hemoglobin level and ICD-9 codes. The incidence of anemia differed by race/ethnicity, stage of disease, presence of concurrent illnesses, and prescription of chemotherapeutic agents (Table 4). Anemia, whether drug-related or unrelated to drugs, was positively associated with clinical AIDS, a CD4 count of <200, bacterial septicemia, neutropenia, thrombocytopenia, prescription of ganciclovir, and prescription of fluconazole and negatively associated with the prescription of TMP-SMX. Additionally, drug-related anemia was positively associated with prescription of ZDV (Table 5). Anemia unrelated to drugs was also associated with black race, female sex, and lymphoma and was negatively associated with prescription of ZDV (Table 5).

Of 19,213 persons included in survival analysis (Table 2), 6,632 (35%) died during follow-up. Median follow-up time for all persons included was 17 months. Survival did not differ significantly for persons with a diagnosis of drug-related anemia versus those with a diagnosis of anemia unrelated to drugs (P = .3 by log rank test), so all anemic persons were considered together in the mortality analysis. Median survival was significantly shorter for persons with anemia than for those without anemia, regardless of first CD4 count (Table 6). Proportional hazards regression was used to control for CD4 count, clinical AIDS, age, neutropenia, thrombocytopenia, antiretroviral therapy, and Pneumocystis carinii pneumonia (PCP) prophylaxis. After controlling for these factors, anemia was significantly associated with increased risk of death at all levels of first CD4 count (Table 6). Stratified proportional hazards regression analysis showed that the effect of anemia on survival differed by first CD4 counts; for persons with a first CD4 count of <200 cells/μL, the risk ratio was 1.56 (99% CI, 1.43 to 1.71; summary data not shown in Table 6), but for persons with a first CD4 count of ≥200 cells/μL, the risk ratio was 2.48 (99% CI, 2.14 to 2.88).

There were 7,261 anemic persons in the initial mortality analysis, of whom 3,203 (44%) had subsequent hemoglobin level determinations and were, thus, also included in analyses of the effect of recovery from anemia on mortality. The results of mortality analyses were not different for persons recovering from drug-related anemia or anemia unrelated to drugs, so all persons with anemia were considered together for these analyses. Of these, 1,341 (42%) were treated with either erythropoietin or blood transfusion and 1,208 (38%) recovered from anemia. Median survival was significantly longer for persons who recovered than for those who did not recover, regardless of first CD4 count (Table 7). When clinical AIDS, CD4 count, neutropenia, thrombocytopenia, antiretroviral therapy, and PCP prophylaxis were controlled, recovery from anemia was significantly associated with decreased risk of death (Table 7); there was no interaction with first CD4 count, and the combined risk ratio was 0.37 (99% CI, 0.33 to 0.43).

We found that anemia is a frequent complication of HIV infection that is associated with an increased risk of death and that recovery from anemia is associated with decreased risk of death for HIV-infected persons who do develop anemia. According to our analysis, for most CD4 strata the median survival for persons who never became anemic was similar to the median survival for those who became anemic but later recovered (Tables 6 and 7).

The incidence of anemia was strongly and consistently associated with the progression of HIV disease as measured by diagnosis of an AIDS-defining opportunistic illness and measurement of a CD4 count of <200 cells/μL. This association is most likely explained by the increasing viral burden as HIV disease progresses, which could cause anemia by increased cytokine-mediated myelosuppression. Alternatively, anemia may be a surrogate marker for some aspect of disease progression not captured by controlling for CD4 count and clinical AIDS diagnosis. When adequate data are available for viral load measurements, quantitative RNA measurements should be included as a covariate in analyses like the ones presented here.

The administration of ZDV is recognized to cause anemia because of myelosuppression.14 In our analysis, the prescription of ZDV was positively associated with a diagnosis of drug-related anemia but was protective against a diagnosis of anemia unrelated to drugs. This protective effect may occur because patients in whom anemia develops while they are prescribed ZDV are likely to be given a diagnosis of drug-related anemia, and the diagnoses of drug-related anemia and anemia unrelated to drugs were mutually exclusive in our analysis. The protective effect may also be explained by the fact that for patients who do not develop anemia related to ZDV and continue to take the drug, ZDV treatment may slow the progression of the HIV disease and the HIV replication rate. Lower viral burden, in turn, may be associated with a decreased incidence of anemia because of less cytokine-mediated myelosuppression. The prescription of ganciclovir, known to cause myelosuppression, was also associated with the incidence of anemia, whether identified as drug related or unrelated to drugs. This suggests that anemia associated with prescription of ganciclovir may be less likely to be recognized or recorded in medical records as drug-related than anemia associated with ZDV prescription. Fluconazole may cause myelosuppression when taken concurrently with ZDV, because taking both reduces the serum half life of ZDV and increases its serum concentrations.26 

An unexpected finding was the negative association between prescription of TMP-SMX and anemia. Although administration of TMP-SMX can cause drug-associated aplastic anemia or immune-mediated destruction of specific populations of blood cells, this effect would not be expected to have a significant influence on the AOR in this analysis because the effect is sporadic.16 It is likely that the protective effect of TMP-SMX is associated with the prevention of other conditions, such as Mycobacterium avium complex27or bacterial septicemia, which are more predictable causes of anemia, or other infections that could promote the development of the anemia associated with chronic disease or with inflammation.

An increased incidence of anemia not recognized as drug related was observed in black persons, although black race was not associated with drug-related anemia. This association could be because of several factors or a combination of these factors. A small percentage of black persons have sickle cell anemia. The prevalence of glucose-6-phosphate dehydrogenase (G-6-PD) deficiency may be 4% to 13% for black men28,29 and 3% for black women.29 For persons with G-6-PD deficiency, dapsone30 or sulfamethoxazole,31 both of which are prescribed for prophylaxis for P carinii pneumonia in patients with HIV infection, may cause hemolytic anemia. Persons with G-6-PD deficiency may also develop hemolytic anemia after infection with certain bacteria (including Salmonella).32 The diagnoses of sickle cell anemia and G-6-PD were not consistently collected in the Adult and Adolescent Spectrum of HIV Disease Project, so a direct evaluation of these hypotheses was not possible. It is also possible that black race is a marker for other factors that are associated with increased incidence of anemia but that were not included in our analysis.

Anemia was also associated with thrombocytopenia and neutropenia, perhaps because myelosuppression caused by chemotherapeutics may affect production of all the cell lineages. The association of anemia with lymphoma may be because of myelophthisis, the secondary effects of therapies administered for lymphoma, or anemia associated with chronic disease. Myelosuppression is commonly observed in patients with bacterial septicemia, regardless of HIV infection status.

For an analysis of factors associated with incidence of anemia, the outcomes of drug-related anemia and anemia unrelated to drugs were evaluated separately because the effect of ZDV prescription, one of the most recognized causes of anemia in HIV-infected persons, differed by type of anemia. Because these two types of anemia were distinguished only on the basis of physician diagnosis as recorded in the medical record, there was no standard criterion for drug-related anemia. The condition may have been under diagnosed or under documented in medical records or the association between ZDV prescription and drug-related anemia could be overestimated if physicians assume a drug-related cause for anemia in a patient who is taking ZDV.

In all analyses, some patients were excluded because of prevalent anemia, inadequate length of follow-up, or missing data that were necessary for our analysis. In general, the characteristics of the patients excluded from the analyses were similar to the characteristics of those who were included (Tables 1 and 2). A possible bias is introduced in the analysis of incidence by including persons who developed anemia during the second semester after baseline review but had no further semester reviews, but not including persons with two semesters of review and no anemia. This tends to cause an overestimate of the incidence of anemia.

The main limitation of our analysis is that outcomes and exposures in this project are reported only as occurring or not occurring in each 6-month interval of chart abstraction, and the exact dates of drug-related anemia diagnosis, concurrent illnesses, or specific drug administration were not collected. Therefore, our ability to define exact temporal relationships between exposures and anemia is limited. Exposures to drugs could occur from 1 day to 12 months before anemia, and this decreases our ability to detect associations between anemia and a drug. This should result in conservative estimates of excess risk. Data that would allow the classification of the cause of anemia, such as reticulocyte counts, erythropoietin levels, and parvovirus IgM titers, were not collected in this project.

The Adult and Adolescent Spectrum of HIV Disease Project includes diverse study sites and populations,24 but these data are not necessarily representative of all HIV-infected persons in the United States. Because HIV-infected patients must have been receiving medical care at a clinic for at least 12 months to be included in our analysis, there may be a selection bias for asymptomatic people with earlier knowledge of HIV infection status or with more access to care.

The definition of anemia chosen for this study (hemoglobin <10 g/dL) was different from clinical reference ranges for hemoglobin concentration in men and women. We chose this cutoff for defining anemia to exclude hereditary causes for mild anemia, such as thalassemia trait, and to allow for use of a single cutoff that would clearly exclude normal hemoglobin concentrations for both men and women. As a result, our estimates of anemia incidence underestimate the true impact of anemia in this population. Physicians should consult their local laboratories to determine appropriate reference ranges for clinical interpretation of hemoglobin concentrations, and any anemia in HIV-infected persons, regardless of severity, should be investigated.

Anemia in HIV-infected patients, if persistent, is associated with substantially decreased survival. Although our analyses cannot show whether this relationship is causal, our findings are consistent with those of other studies of anemia as a prognostic factor in HIV infection,20 21 and consideration should be given to evaluating the effects of treating anemia in a prospective study design. If recovery from anemia is shown to directly increase survival, screening for anemia should be aggressive and patients with anemia should be treated.

The Adult/Adolescent Spectrum of HIV Disease Group includes Susan Burkham, MPH, Texas Department of Health, Austin, TX; Susan Buskin, PhD, Seattle-King County Department of Public Health, Seattle, WA; Arthur Davidson, MD, Denver Department of Health and Hospitals, Denver, CO; A.D. McNaghten, PhD, Michigan Department of Public Health, Detroit, MI; Kaye Reynolds, Department of Health and Human Services, Houston, TX; Frank Sorvillo, PhD, Los Angeles County Department of Health Services, Los Angeles, CA; Melanie Thompson, MD, AIDS Research Consortium of Atlanta, Atlanta, GA; and Susan Troxler, RN, MPH, Louisiana Department of Health, New Orleans, LA.