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CD4 Count/CD4 percent - What's the difference?

Jul 31, 1998

I recently submitted a question related to an undetectable (less than 400) PCR viral load without taking any medication. You asked if my white blood cells were ok. Well I can compare two blood tests one from June and one a year ago. Well except for my leucocytes (sorry /spelling) which were at 4000/mm3 a year ago and now at 3700, the rest stayed within close ranges. I'm working on getting tested for VL and CD4 again (last CD4 was 191 count, 33,8 %), which leads to my question for this time: What is the relation between the CD4 count and CD4 percent? My results have been 526 count, 28 %; 364, 26,3%; 592, 23,9 %, and 191, 33,8 %. Why does each (count/percent) seem to go its own way? I wonder because with my last VL, I'm thinking if I shouldn't be changing the lab.

Thanks for your help. Really, so far I haven't found another site this helpful!

Response from Dr. Holodniy

There seems to be a fair amount of variability in these numbers. In clinically stable patients over a few month period, you wouldn't expect to see more than a 1-2% difference in CD4%, and <50 CD4 absolute number change. If those numbers are from the last year, a 10% swing in CD4% and 400 cell swing in absolute CD4 number, would make me think about assay issues. One usually starts with a total white blood count. Then the total number of lymphocytes is counted on the same machine. The percentage of CD4 and CD8 cells are obtained on a separated machine. The absolute number of CD4 cells is obtained by calculating this number from the absolute number of total lymphocytes times the CD4%. I don't want to make this a math lesson, but.... If your total white count is 4500, total lymphocyte count of 1500 and 33% CD4, the absolute CD4 number if 500. If your white cell count is 3000, lymphocyte count now 1000, 33% CD4, your absolute number will be 330. Lastly absolute counts usually go with percentage. So in rough terms, with 30% CD4, the count is 500. With a 20%, count is 300, 10% count is 100. Your count of 191 and 33% is not consistent, unless the total number of white cells is low. Hope this is not confusing. It's late.


Blue Cross Blue Shield won't pay for my VL Test
Low CD4 undetectable VL = healty?

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