In order to understand the diagnosis we first must be able to understand the meaning behind testing and ordering these two particular tests.
Serum creatine is used to diagnose impaired renal function with a critical value of >4 mg/dL indicating serious impairment.
BUN or Blood Urea Nitrogen testing us used as an indirect and rough measurement of renal function and glomerular filtration rate while also being a measurement of liver function.
with this BUN contain a higher list of interfering substances that can alter test results then serum creatine and include things such as changes in protein diet, amount of muscle mass, pregnancy, gastrointestinal bleeding, over-hydration and dehydration, drugs such as but not limited to allopurinol, ahminoglycosides, cephalosporins, etc.
Now in our case since BUN is high (since we don't have a value or any other information we are guessing) now possible medical diagnosis would include dehydration, congestive heart failure without renal involvement, a gastrointestinal bleed, an increase of protein diet, and undergoing a catabolic state due to trauma, infection, or (like sepsis), starvation, and the use of certain drugs such as corticosteroids.