TOC |  ID  |  AIDS


T-lymphocyte cell Count  (CD4)

It is the officially called "CD4+ T-lymphocytes."   The virus that causes AIDS attacks CD4 cells. HIV invades your CD4 cells and uses them as a breeding ground for new virus particles.  Eventually the CD4 cell is killed by the virus. As the number of CD4 cells decreases, your risk of getting a severe disease -- or "opportunistic illness" -- increases.

Your disease classification -- asymptomatic, ARC, or AIDS
-- is based on the lowest t-cell test you ever had. For example, if you once tested at 180 ... but then got a big boost from a new protease inhibitor ... you are still considered in Category 3.

The Definition Of AIDS

Category 1 (Asymptomatic HIV Disease) -  CD4 > 500 cells/mL

You are in Category 1 only if you are asymptomatic (no symptoms) and have never had less then 500 CD4 cells.   If you have had any of the AIDS-defining diseases listed for categories 2 or 3, then you are not in this category.  
If your t-cell count has ever dropped below 500, you are not at Category 1.

The clinical categories of HIV infection are defined as follow:

Clinical Category A
Category A consists of one or more of the conditions listed below in an adolescent or adult (greater than or equal to 13 years) with documented HIV infection. Conditions listed in Categories B and C must not have occurred.

Category 2 (ARC)  -  CD4  200-499 cells/mL

You are in Category 2 if --  

1. your T-cells have dropped below 500 but never below 200; and, -- or --

2. you have never had any Category 3 diseases (see below)
    but have had at least one of the following defining illnesses --

According to the U.S. government, Category 2 means the immune system shows some signs of damage but it isn't life-threatening.

Clinical Category B
Category B consists of symptomatic conditions in an HIV-infected adolescent or adult that are not included among conditions listed in clinical Category C and that meet at least one of the following criteria:

Category 3 (Symptomatic HIV Disease, AIDS)  -  CD4 < 200 cells/mL

You are in Category 3 (i.e., you have "AIDS") if --

1.your T-cells have dropped below 200;   -- or -- have had at least one of the following defining illnesses --

** Added in the 1993 expansion of the AIDS surveillance case definition.

Clinical Category C

Category C includes the clinical conditions listed in the AIDS surveillance case definition (Appendix B). For classification purposes, once a Category C condition has occurred, the person will remain in Category C.


Conditions included in the 1993 AIDS surveillance case definition

  1. Candidiasis of bronchi, trachea, or lungs
  2. Candidiasis, esophageal
  3. Cervical cancer, invasive**
  4. Coccidioidomycosis, disseminated or extrapulmonary
  5. Cryptococcosis, extrapulmonary
  6. Cryptosporidiosis, chronic intestinal (greater than 1 month's duration)
  7. Cytomegalovirus disease (other than liver, spleen, or nodes)
  8. Cytomegalovirus retinitis (with loss of vision)
  9. Encephalopathy, HIV-related
  10. Herpes simplex: chronic ulcer(s) (greater than 1 month's duration); or bronchitis, pneumonitis, or esophagitis
  11. Histoplasmosis, disseminated or extrapulmonary
  12. Isosporiasis, chronic intestinal (greater than 1 month's duration)
  13. Kaposi's sarcoma
  14. Lymphoma, Burkitt's (or equivalent term)
  15. Lymphoma, immunoblastic (or equivalent term)
  16. Lymphoma, primary, of brain
  17. Mycobacterium avium complex or M. kansasii, disseminated or extrapulmonary
  18. Mycobacterium tuberculosis, any site (pulmonary** or extrapulmonary)
  19. Mycobacterium, other species or unidentified species, disseminated or extrapulmonary
  20. Pneumocystis carinii pneumonia
  21. Pneumonia, recurrent**
  22. Progressive multifocal leukoencephalopathy
  23. Salmonella septicemia, recurrent
  24. Toxoplasmosis of brain
  25. Wasting syndrome due to HIV

** Added in the 1993 expansion of the AIDS surveillance case definition.