Why urea level elevated after treatmen of leukemia?

Hi BUN+leukemia : This can be due to enhanced tissue breakdown (catabolic state) caused by specific anti-leukemeic therapy. Glucocorticoid used in some chemo protocols can also cause this. Perenal azotemia similar to dehydration, certain medication and high protein intake are others. Depending on your specific situation, upper gastrointestinal bleeding is possible and this too can cause an elevated bun.

Actually a complex ?: Many possible reasons. Depends upon what you mean by after treatment...Leukemia infiltration of kidneys? Tumor lysis syndrome? Chemotherapy toxicity? Catabolic state while on steroids, prerenal azotemia secondary to cardiac dysfunction or volume depletion, etc. Can you give further details? If so, we can be much more helpful.