High BUN-to-creatinine ratios occur with sudden (acute) kidney failure. This may be
caused by shock or severe dehydration. A very high
BUN-to-creatinine ratio may be caused by bleeding in the
Low blood creatinine levels can mean lower muscle mass caused by a disease, such as
muscular dystrophy, or by aging. Low levels can also mean some types of severe
liver disease or a diet very low in protein. Pregnancy can also cause low blood
Low creatinine clearance levels can mean you have chronic kidney disease or serious kidney damage. Kidney damage can
be from conditions such as a life-threatening infection, shock, cancer, low
blood flow to the kidneys, or urinary tract blockage. Other conditions, such as
heart failure and dehydration, can
also cause low creatinine clearance levels.
Low BUN-to-creatinine ratios may be linked with a diet low in protein, a severe
muscle injury called rhabdomyolysis, pregnancy, cirrhosis, or syndrome of
inappropriate antidiuretic hormone secretion (SIADH). SIADH sometimes occurs
with lung disease, cancer, diseases of the central nervous system, or the use
of certain medicines.
What Affects the Test
You may not be able to have the test, or the results may not be helpful, if:
You take certain medicines, such as:
The antifungal medicine amphotericin B, cimetidine
(Tagamet), phenytoin (Dilantin), quinine, quinidine, procainamide, methyldopa, trimethoprim (Proloprim, Trimpex), or vitamin C (ascorbic acid).
Cephalosporin antibiotics, especially
cefoxitin (Mefoxin), tetracycline antibiotics, and some
You do some strenuous exercise 2 days before
a creatinine clearance test.
You eat more than
8 oz (227 g) of meat,
especially beef, in the 24 hours before a blood creatinine test or during a
creatinine clearance urine test.
You don't collect your urine for exactly 24 hours.