Thank you for your question.
There is a strong possibility of the garlic smell being related to one of the supplements that he is on.
So I would not worry too much about the garlic smell itself being an indicator of anything serious.
However, if his blood counts do not improve even after taking supplementation for a month or two then the next step is diong a bone marrow biopsy to see exactly what's going on and to definitively rule out anything serious.
However, it would be VERY UNLIKELY to be anything serious like cancer from what you are mentioning because had that been the case the doctors would have known it already.
Leukemia usually does not cause low white cell count (although possible but pretty rare to say the least, he would be very sick if that were the case).
It usually causes a high white cell count with low red cell counts and platelets.
Let me know if you have more questions
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