How Can a Doctor Determine Dehydration Using the BUN-to-Creatinine Ratio?

A doctor can diagnose dehydration when the BUN-to-creatinine ratio is high, reports WebMD. A high BUN-to-creatinine ratio occurs when BUN levels are higher than creatinine levels.

A blood urea nitrogen, or BUN, test is used to determine if the kidneys are functioning properly, explains WebMD. Urea is a waste product developed in the liver during protein breakdown and is eliminated through urine. Nitrogen is a by-product of urea, and the amount of urea nitrogen in the blood is measured by a BUN test. When the kidneys are unable to eliminate urea from the blood properly, BUN levels rise. Dehydration, heart failure and a high protein diet can cause elevated BUN levels.

Creatinine is another waste product found in the blood and urine, states WebMD. When food is converted into energy through metabolism, creatine is formed. Creatine is further broken down into creatinine, which is removed from the blood by the kidneys and then eliminated through urine. Kidney damage is manifested by higher creatinine levels in the blood and lower levels in the urine. Dehydration, consuming large amounts of meat, taking some medications and the dietary supplement creatine can increase creatinine levels, explains Mayo Clinic. Creatinine in the blood also increases with increased muscle mass.