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Lymphocyte Doubling Time

Date: January 23, 2024

I received some recent email from patients on the subject of lymphocyte doubling time (LDT) and how to calculate it. Old timers who have been around the block and know all about this can skip the rest of the message. For the newcomers to this disease, one of the “low tech” prognostic indicators used is how fast the WBC (white blood count) or more accurately the ALC (absolute lymphocyte count, calculated by multiplying the WBC by the percent lymphocytes in the blood) is increasing. Sounds reasonable ― it should give you a fool-proof idea how fast the cancer is growing inside you, right? Wrong! Not so fast. Before you get fixated on the monthly numbers you need to know a few things on how to interpret the data.

For starters, CLL resides in many locations in your body, such as your bone marrow, lymph nodes, spleen, liver and blood. As a rule of thumb, the number of CLL cells circulating in your blood are often no more than 5-10% of the total number of cancer cells in your body, the count in your blood is truly no more than the tip of the iceberg. The 5-10% number is quite variable as well. Some patients start out with huge lymph nodes and bone marrow infiltration and hardly anything in the blood. This is quite common in patients with 11q deletion, for example, and it is also a fact of life for later stage CLL patients. Patients with SLL (small lymphocytic lymphoma) also have most of the disease centered in their lymph nodes, the word “lymphoma” in this name is used to distinguish these patients from more classic CLL patients, who have more of their CLL cells circulating in the blood. As you can see, the monthly blood test is hardly an accurate description of the true state of affairs. It is at best a murky reflection of the disease. The reason why the monthly blood test is popular is because it is cheap and easy to do. I can hang out a shingle and make lots of money counseling all the patients who freak out unnecessarily on account of a minor blip in the monthly numbers.

In addition to this baked-in-the-cake problem of the relevance of blood numbers, WBC and ALC can have random variations of any where from 5 to 10K (or more), depending on a variety of factors. Some of the more common ones are the lab that is doing the testing (equipment used, lab tech doing the test), the level of hydration of your body at the time the blood was drawn, how much exercise you have just had prior to blood draw, the time of day, any minor infection you might not even know you have (a bug bite, a recent scrape of the knee, the phase of the month if you are a young woman, the list goes on). If you wish to minimize the fluctuations, it is a good idea to have the same lab (same equipment) do the test each time, and try to get the blood drawn at about the same time of the day.

But realistically speaking, there is no way of avoiding random fluctuations altogether. The best way of getting a reliable handle on how your ALC is progressing is to collect and plot your monthly data on a chart, over a long enough period of time. If you use spreadsheet software such as Excel, you can have the computer draw best-fit lines through the data points and you will be able to see the trends better. A picture is worth a thousand words. It also helps to see the scatter of the data points from the trend line as this will give you a better feel for the degree of random fluctuations.

By the way, all the sophisticated mathematical equations for calculating lymphocyte doubling time are worth exactly as much as the validity of the two data points that are input into the equations. The phrase 'garbage in, garbage out' is worth remembering in this context. The best way of figuring out your doubling time is to look at the long term trend of your numbers, pick two points in time (over a sufficiently long period) where the trend line shows the numbers have doubled. That is your doubling time.

If you have not done so already, I suggest you visit the Your Charts page on Topics, where we have a set of sample charts as well as a formatted blank set that you can download to your computer and use to track your own numbers. Many of our patients have found these charts useful. In addition to tracking ALC, it is also a good idea to track your red blood cell indices RBC (red blood cell count), Hg (hemoglobin level), HCT (hematocrit), ANC (absolute neutrophil count; some labs report only granulocyte counts as a substitute), and Plt (platelet count). Again, don't drive yourself crazy with each monthly fluctuation in these numbers, it really is all about the trends observed over a long time.

I hope you are familiar with Excel, since that is the software I used to generate the charts. If you have questions on how to download the charts or related matters, you should write to pc@clltopics.org. He is our webmaster and software expert extraordinaire, and I am but a mere user of Bill Gates' bounty. There is also quite a bit of help on how-to in this section of the website which might have the answers for which you are looking.

Be well,

Chaya
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