I am concerned that my wife's WBC has dropped 1/3 in only 6 weeks of using Tecfidera. Initial WBC was 900, and now WBC is 600. I am concerned with a consistent decrease, or is this the normal reduction level? It was suggested to wait 12 weeks for next WBC check up. Is this normal, or should she get it checked sooner?
This is a very good question. First off, I suspect the numbers you provided in your question refer to absolute lymphocyte counts NOT the white blood count or WBC. The WBC includes all the white blood cell types including neutrophils, monocytes, eosinophils and lymphocytes. If these numbers referred to your wife’s WBC, then her counts would have been dramatically low even before starting treatment with tecfidera, since a normal WBC is greater than 3,500.
Even absolute lymphocyte counts (ALC) are usually above 900, so if these numbers are correct her counts were low at the beginning of treatment. In my experience lymphocyte counts drop quickly after starting tecfidera with most individuals reaching their lowest counts between 6 and 12 months after start of treatment.
The frequency with which blood counts should be monitored in patients on Tecfidera is unclear. I usually do not recheck lymphocyte counts until 6 months after starting the drug. If lymphocyte counts are low, defined as an absolute lymphocyte count less than 600, I repeat the counts in about 1 month. I typically discontinue Tecfidera in anyone with a persistent reduction in absolute lymphocyte counts below 500 for more than one month in the absence of another reason for a low lymphocyte count. Other physicians may discontinue Tecfidera if the low counts persist for more than 3 months.
Generally speaking low lymphocyte counts do not immediately increase the risk of infections or tumors; these risks take time to develop unless the counts drop very low very quickly. This is in contrast to low neutrophil counts (as occurs with chemotherapy treatment) which increase the risk of infection immediately.
I hope this helps.
Revere (Rip) Kinkel, MD
Director of the UCSD Multiple Sclerosis Center