CD4 counts and total lymphocyte count?
Aug 26, 1996
From what I have read here, I imagine that if one person tests positive for HIV,the next step is to measure the CD4 count, right?Is this a special analysis? If the number is ok, how often is it repeated inorder to control the evolution of HIV?Low CD4 counts mean overall low leucocyte count?? or lymphocyte count??
Response from Dr. Cohen
Yes, after testing positive for HIV, the next step is to measure the CD4 count (as well as some other tests, usually including viral load). I suppose you could call the CD4 count a "special analysis" in that it needs to be ordered -- you won't get CD4 results through routine blood tests. It is usually repeated every three months (sometimes less often if it is very high), also along with the viral load.
When you order a complete blood count, you get a hematocrit and hemoglobin (which tell you about red blood cells) and a white blood cell count. A "differential" then tells you about the different types of white blood cells: what percentage are neutrophils, lymphocytes, monocytes, etc. With HIV we're particularly interested in the lymphocytes. The total white blood cell count multiplied by the percentage of lymphocytes from the differential gives you the absolute lymphocyte count. Then we want to know how many of those lymphocytes are CD4 lymphocytes (also known as T-helper cells). When you multiply that by the CD4 percentage (determined by the CD4 test), you get the absolute CD4 count, the number we use to determine stage of HIV infection, risk of complications, need for therapy, etc.
If you like math, you can look at it this way:
WBC x % lymphocytes x %CD4 = absolute CD4 count
You can see that any variation in the total white blood cell count or lymphocyte count could affect your CD4 count. That's the reason that some people prefer to talk about the CD4 percentage, which is less variable. We're more accustomed to the absolute count, so that's used more frequently, but the percentage can often be helpful in interpreting confusing or inconsistent results.
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