Difference between CD4 count and absolute %
Sep 12, 2004
I'm totally confused about the difference between absolute numbers and the %. I just found out that my cd4 cout was 28% or 392. How is the percent more meaningful than the absolute number? I just don't get this...
Response from Dr. Young
Thanks for your question.
Both tests are ways of estimating the level of CD4-positive T cells in the body. The CD4% looks at the percentage of cells that are CD4+, whereas the absolute number takes the percentage and multiplies this by the total number of lymphocytes (part of the white blood cells). From this, you can see that the absolute number is influenced by the overall traffic of cells (much like traffic on the highway-- higher at rush hour, lower at midnight). This is why many look at the CD4% as a less variable number than the absolute CD4 count.
On average, a CD4 count of 200 is equivalent to a percentage of 15; each 100 cells is roughly 7% points. From this you can see that a percentage of ~30% should be equivalent to an absolute count of about 400-- precisely what your labs have shown.
In practical terms, I use both sets of numbers to get a rough estimate of how my patient's immune system is doing. If the paired percentage and absolute counts are in disagreement, then I'll look at the one that is the "lowest" in trying to assess risk of an HIV complication.
I hope this clears things up. Thanks for reading. BY
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