Reliability and validity of self-report CD4 counts-in persons hospitalized with HIV disease

Studies of health care outcomes and clinical decision making for people with HIV disease depend on CD4 cell count data to accurately assess the stage of disease. The possibility of obtaining reliable and valid data from self-reported CD4 counts is an unexplored source of potentially important, cost-effective information for these purposes. We examined the extent of agreement of self-reported CD4 counts with medical record CD4 among 120 patients (95% male, 69% white, 5% injection drug users) hospitalized with HIV-related illness at seven Los Angeles area hospitals. Average record and report CD4 counts did not differ significantly, and record and report CD4 counts were highly correlated (product moment correlation of 0.84, intraclass correlation of 0.82). Agreement between self-reports and medical records varied by CD4 level: at higher levels of CD4, the differences between self-reports and medical records tended to be larger, with self-reports yielding upwardly biased estimates compared to the medical records. These findings suggest that self-report CD4 data may provide clinically adequate estimates of true CD4 counts. The study needs to be replicated in other populations, notably those with larger numbers of subjects who are female, of minority ethnicity, or injection drug users.