- variations account for the wide range in normal values (usually about 500 to 1400 cells/mm3) and reflect the fact that the CD4 cell count is the product of three variables: the white blood cell count, percent lymphocytes, and the CD4 percentage. There are also seasonal changes (Clin Exp Immunol 1991;86:349) and diurnal changes, with the lowest levels at 12:30 PM and peak values at 8:30 PM (JAIDS 1990;3:144); these varia - tions do not clearly correspond to the circadian rhythm of corticosteroids. Modest decreases in the CD4 cell count have been noted with some acute infections and with major surgery. Corticosteroid administration may have a profound effect, with decreases from 900 cells/mm3 to less than 300 cells/mm3 during acute administration; chronic administration has a less pronounced effect (Clin Immunol Immunopathol 1983;28:101).Medical conditions associated with low CD4 counts include Sjogren syndrome, sarcoidosis, radiation, atopic dermatitis, collagen-vascular disease, lymphoma, stem cell transplant recipients and idiopathic CD4 lyphopenia (see pg 28). Acute changes are probably due to a redistribution of leukocytes between the peripheral circulation and the marrow, spleen, and lymph nodes (Clin Exp Immunol 1990;80: 460).
- Deceptively high CD4 counts may occur with HTLV-1 co-infection or splenectomy. HTLV-1 is closely related to HTLV-2, and most serologic assays do not distinguish between the two, but only HTLV- 1 causes deceptively high CD4 cell counts. Serologic studies in the United States show HTLV-1 or 2 infection rates of 7% to 12% in injection drug users and 2% to 10% in commercial sex workers (NEJM 1990;326:375; JAMA 1990;263:60; STD 2000;27:87); 80% to 90% of these are a result of HTLV-2 infection in both populations. High rates of con current HIV and HTLV-1 have been reported in Brazil (JAMA 1994;271:353) Peru and Haiti (J Clin Microbiol 1995;33: 1735). Analysis of patients with co-infection suggests that CD4 counts are 80% to 180% higher than in controls for comparable levels of immunosuppression (JAMA 1994;271:353). Some work suggests HTLV-2/HIV-1 co-infection has a favorable effect on the natural history of HIV infection (AIDS Rev 2007;9:140). Splenectomy results in a prompt, sustained increase in CD4 count. The CD4 percentage more accurately reflects immunocompetence in splenectomized patients (CID 1995;20:768; Arch Surg 1998;133:25). The following have minimal effect on the CD4 cell count: gender, age in adults, risk category, psycho logical stress, physical stress, and pregnancy (Ann Intern Med 1993;119:55).
- CD4 Percentage: The CD4 percentage is sometimes used because it reduces variability to that of a single measurement (JAIDS 1989;2:114). In the ACTG laboratories, the within-subject coefficient of variation for CD4 percentage was 18% compared with 25% for
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