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Dr. Susan Leclair Explains Lymphocyte Doubling Time

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Published on February 26, 2013

Laboratory scientist Dr. Susan Leclair explains the significance of lymphocyte doubling time (LDT). If the cells are living longer or shorter spans, why? Learn about smudge cells and a clever formula for determining your LDT.

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Transcript | Dr. Susan Leclair Explains Lymphocyte Doubling Time

Please remember the opinions expressed on Patient Power are not necessarily the views of our sponsors, contributors, partners or Patient Power. Our discussions are not a substitute for seeking medical advice or care from your own doctor. That’s how you’ll get care that’s most appropriate for you.

Andrew Schorr:

Hello and welcome to Patient Power.  I’m Andrew Schorr. 

One of my favorite people in the healthcare field is Dr. Susan Leclair.  She is an expert in laboratory science, and I know I’ve learned a lot from her, and now she’s a Patient Power contributor, and we are thrilled.  In this segment she tells us about LDT, or Lymphocyte Doubling Time, which she feels it’s very important that each CLL patient understand, in their own situation, their LDT.  Are cells living longer, and are they multiplying faster?  Here’s Susan. 

Dr. Leclair:

Lymphocyte doubling time is a test that has come into popular use in, I would say, the last 10 years, and the issue here is that we need to know how long a cell lives, in order to be able to determine whether it is doubling just because of its age, it’s hanging around longer, or whether there’s actually an aggressive turnover.  The slide shows red cells only because it is an easier example to use because we know that red cells live for 120 days.  We know that.  That’s the rule. 

If for some reason a population of red cells lived 240 days instead of 120, you can kind of do the math really easy.  If you started off with 5 million cells, as the slide says, you’d have twice as many cells in 120 days, because these cells are still living, they’re still around, they’re still active in some way, and so you get an absolute increase in the number of cells in your body simply because they live longer. 

And that’s an issue.  Are the cells in CLL just living longer, or are they actually multiplying at a faster rate?  Now, we know, unfortunately, CLL cells do live longer.  They do.  We also know that some of them, though, die easier.  Most of you, who have got your CBC reports, know that occasionally there’s something called a smudge cell.  It’s a dead lymphocyte.  In order for these cells to keep increasing in number there’s got to be a combination of living longer and undergoing mitotic division to get bigger numbers. 

And here’s why this is important: Because more aggressive cells live longer and more aggressive cells multiply more frequently.  If I have a situation where someone’s white count has gone from 10,000 to 20,000 to 30,000 to 40,000 over a very small span of time, I know these cells are super aggressive, and I know that that probably means there’s going to be consequences to that.  If on the other hand, in every six months you have 10,000 cells to 12,000 cells to 13.5,000 cells, then they’re going much slower, and I know that there’s a longer time between having to deal with consequences. 

Now, there’s a really complicated formula that you can use, that physicians use to determine lymphocyte doubling time, but if you’re sitting on your Excel spreadsheet right now and you want to find out what your lymphocyte doubling time is, approximately, take your last two CBCs.  In each one of them there will be an absolute lymphocyte count.  Take today’s absolute lymphocyte count and the last time’s lymphocyte count and see what the difference is, by subtracting the previous one from today’s count.  The smaller that number, the less chance you have of consequences in the near future.  The larger that number, the more there is a chance for consequences. 

Most physicians don’t want to see a doubling time that occurs within a year.  As long as your white count doesn’t double within a year you’re in pretty good at not having very good consequences or very big consequences showing up.  If that makes any sense, fine, and if it doesn’t, write to me at comments@patientpower.info and I’ll see what I can do. 

Andrew Schorr:

Thank you for joining us.  Dr. Susan Leclair will be back with more important information for you, the patient, as we continue our series with her.  We’re delighted to have her as a Patient Power contributor. 

I’m Andrew Schorr.  Remember, knowledge can be the best medicine of all. 

Please remember the opinions expressed on Patient Power are not necessarily the views of our sponsors, contributors, partners or Patient Power. Our discussions are not a substitute for seeking medical advice or care from your own doctor. That’s how you’ll get care that’s most appropriate for you.

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