In gral. "acute" means of "recent" origen, and "chronic" means "old" or less recent.
Some classifications use 6 months for "subacute". Chronic renal failure is insidious and depends upon the cause and how fast it gets worst. Acute renal failure
usually is caused by low fluid volume in the body either dehydration
or bleeding or it may be caused by toxins (poison, medications , dye contrast).