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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.

MH



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