Creatinine 1.5 but bun in normal range. i thought both creatinine and bun increase at the same time. what could cause this?

Look at GFR: Creatinine and BUN are 2 different ways of assessing the filtration of your kidneys. The true measurement of your filtration is the GFR (glomerular filtration rate). We typically use BUN to Creatinine ratios to decipher the underlying cause of any mild renal injury. Creatinine 1.5 is near normal. BUN-Creat ratio of >20 typically is related to dehydration. Hope this helps.