Yes, a retest is called for ... should be no issue.
On fasting... I am in the middle of a 3 day fast right now. Mostly because I did the opposite during Christmas !!
A theory is that during a fast the body switches from glucose burning to ketone burning and in the absence of calories, old blood cells (mostly white blood cells) are recycled for their proteins. During a multi-day fast, fewer blood cells are made. However, once re-feeding occurs, signals are released to the bone marrow stem cells to get busy and regenerate the immune system:
It is my thinking that both leukemic and normal stem cells are activated. Both are told to divide. In the case of leukemic stem cells, the act of coming out of hiding and dividing exposes them to the killing power of a tyrosine kinase inhibitor (TKI). They become vulnerable to apoptosis and die. So fasting may be a way (my opinion only) to cause CML stem cells to be greatly reduced below disease initiating threshold in the presence of a TKI. Repeated cycles of multi-day fasting may be enough to insure treatment free remission success. That's my goal anyway.
It is interesting to note that there is evidence (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5300768/) that fasting alone may be sufficient to impact leukemia negatively by inducing rapid differentiation of higher order cells. Keep in mind leukemia kills (all kinds of leukemia) by an ever increasing burden of non-differentiated blast cells. Getting these cells to differentiate and die off naturally is a strategy currently being researched. Vitamin D helps blast cells (leukemic included) to differentiate and apparently so does fasting. The mechanisms are not well understood.
I have found, however, that fasting along with low carb re-feeding is just better living. My weight is down to near grad school days (I'm thin again), I don't get hungry for late afternoon snacks and I just simply feel energetic. Carbs are fine if you are an athlete - you burn what you eat. But for older folks, burning mostly ketones instead of sugar helps the brain and may just cause CML cells to have a hard time. I will do anything that gives CML cells a hard time ... Just so long as trying is not harmful in itself.