Why the hospital my bun was 25. my creatinine was 1.31 my kidney function was 70. they called it acute kidney injury but they didn't do anything about it?

Here are some...: Before drawing a conclusion, the reported data suggesting renal function should be compared & correlated with clinical pictures and serial tests over time; in fact, these could be "normal" for you at this time. If clinically warranted, a formal evaluation, urinalysis, and renal ultrasound may be required, but surely not urgent if lacking undesirable Hx in urinary tract. More? Ask doc timely.

Don't worry.: your kidney function of 70 is the estimated glomerular filtration estimate,(GFR), based on your creatinine level. 60 to 90 is considered stage 2 chronic kidney disease. Usually, improved hydration and verify a normal blood pressure, and avoid NSAIDs like Advil and Aleve (naproxen).