See Kat's response.
Blasts % is reported with every CBC and if zero blasts, often not reported at all.
Blast cells are very fast differentiating cells. They do not stay long as blast cells .... sort of like muons.
If Blast cells are measured in significant amounts, something is wrong - hence importance in leukemia.
Most people have zero to a few percent. Zero doesn't mean none - we all have lots of blast cells created, they just don't stick around.
In CML, blast cells do not differentiate and instead accumulate. This is the part of the disease that kills. When blast cells accumulate in sufficient quantity because they are not differentiating - it's hard to undo - sort of like a roach infestation. Need to burn the house down otherwise known as a stem cell transplant.
Interestingly. Vitamin D is necessary for blast cells to differentiate including leukemic blast cells.
In fact, vitamin D receptors are on blast cells including leukemic blast cells in large number. Without vitamin D, differentiation is slowed down or stalled.
In my own case, I always had blast cells. At diagnosis, my blast cell count was very high bordering on accelerated phase. My vitamin D status was also very low. Even during treatment, my blast cell count was never normal. ONCE I started my vitamin D protocol raising vitamin D from 17 ng/ml to around 70 ng/ml where it is today, my blast cell count fell to zero. It has been zero ever since.
More than any other indicator - blast cell percentage informs whether you have time to experiment with drug dose an other protocols. As long as blast percentage is zero or a few percent - ideally zero, one can experiment with dose and other trials because CML is a very slow disease when in chronic phase.
(I wonder if I ever would have developed CML in the first place if I had known about vitamin D's importance to the immune system and cell differentiation and kept my vitamin D level where it is today. I know of no one who had high normal vitamin D level at diagnosis. It seems low vitamin D is a requirement to trigger the disease among other things going wrong. It's not a cure, but could have, perhaps, been a preventive.)