Page 22 - HIV/AIDS Guidelines

CD4 T-Cell Count (Last updated January 10, 2011; last reviewed January 10, 2011)
The CD4 count serves as the major laboratory indicator of immune function in patients who have HIV
infection. It is one of the key factors in deciding whether to initiate ART and prophylaxis for opportunistic
infections, and it is the strongest predictor of subsequent disease progression and survival according to
clinical trials and cohort studies. 1-2 A significant change (2 standard deviations) between two tests is
approximately a 30% change in the absolute count or an increase or decrease in CD4 percentage by 3
percentage points.

• Use of CD4 Count for Initial Assessment. The CD4 count is one of the most important factors in the
decision to initiate ART and/or prophylaxis for opportunistic infections. All patients should have a baseline
CD4 count at entry into care (AI). Recommendations for initiation of ART based on CD4 count are found
in the Initiating Antiretroviral Therapy in Antiretroviral-Naive Patients section of these guidelines.

• Use of CD4 Count for Monitoring Therapeutic Response. An adequate CD4 response for most
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patients on therapy is defined as an increase in CD4 count in the range of 50–150 cells/mm per year,
generally with an accelerated response in the first 3 months. Subsequent increases in patients with good
virologic control show an average increase of approximately 50–100 cells/mm per year for the
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subsequent years until a steady state level is reached. Patients who initiate therapy with a low CD4 count
or at an older age may have a blunted increase in their count despite virologic suppression.
Frequency of CD4 Count Monitoring. In general, CD4 counts should be monitored every 3–4 months to
(1) determine when to start ART in untreated patients, (2) assess immunologic response to ART, and (3)
assess the need for initiation or discontinuation of prophylaxis for opportunistic infections (AI).
The CD4 cell count response to ART varies widely, but a poor CD4 response is rarely an indication for
modifying a virologically suppressive ARV regimen. In patients with consistently suppressed viral loads who
have already experienced ART-related immune reconstitution, the CD4 cell count provides limited
information, and frequent testing may cause unnecessary anxiety in patients with clinically inconsequential
fluctuations. Thus, for the patient on a suppressive regimen whose CD4 cell count has increased well above
the threshold for opportunistic infection risk, the CD4 count can be measured less frequently than the viral
load. In such patients, CD4 count may be monitored every 6 to 12 months, unless there are changes in the
patient’s clinical status, such as new HIV-associated clinical symptoms or initiation of treatment with
interferon, corticosteroids, or anti-neoplastic agents (CIII).

Factors that affect absolute CD4 count. The absolute CD4 count is a calculated value based on the total
white blood cell (WBC) count and the percentages of total and CD4+ T lymphocytes. This absolute number
may fluctuate among individuals or may be influenced by factors that may affect the total WBC and
lymphocyte percentages, such as use of bone marrow–suppressive medications or the presence of acute
infections. Splenectomy 4-5 or coinfection with human T-lymphotropic virus type I (HTLV-1) may cause
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misleadingly elevated absolute CD4 counts. Alpha-interferon, on the other hand, may reduce the absolute
CD4 number without changing the CD4 percentage. In all these cases, CD4 percentage remains stable and
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may be a more appropriate parameter to assess the patient’s immune function.

References

1. Mellors JW, Munoz A, Giorgi JV, et al. Plasma viral load and CD4+ lymphocytes as prognostic markers of HIV-1
infection. Ann Intern Med. 1997;126(12):946-954.
2. Egger M, May M, Chene G, et al. Prognosis of HIV-1-infected patients starting highly active antiretroviral therapy: a
collaborative analysis of prospective studies. Lancet. 2002;360(9327):119-129.

Guidelines for the Use of Antiretroviral Agents in HIV-1-Infected Adults and Adolescents C-4

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