Is dehydration responsible for abnormal kidney test results?

Dr. Keith Roach

Question: I am a female, nearly 55 years old. In August 2011, I was fortunate to receive a heart transplant (I had an enlarged, weakened heart that was thought to have started with a virus). Since then, I’ve done very well; I go for a checkup every three months. My bloodwork has always shown abnormal numbers for kidney function. My doctor says I am dehydrated, and advises me to drink, drink, drink!

This happened again at my most recent appointment in October, and now there is a patient portal that allows me to view my lab results.

Again, there were abnormal numbers for kidney function. Again, I was told to drink. So for a full week, I drank 4 liters of water every day. Then I returned for bloodwork. My kidney numbers weren’t improved. I have a BUN of 29 and a creatinine of 1.66.

I am concerned that for all these years, something was wrong with my kidneys and was written offff as dehydration.

I take lisinopril daily. — S.I.

Answer: Abnormal blood test results for creatinine and BUN are common and need to be interpreted cautiously. BUN and creatinine both represent waste products in the blood that are fifiltered out by the kidney; so, in general, the higher those numbers, the worse the kidney function. In your case, I suspect there are several reasons for the moderately high numbers.

First, lisinopril routinely causes the creatinine to be elevated, by as much as 25 percent. This is because lisinopril causes less blood to be fifiltered by the kidney every minute, not because it damages the kidney.)

If the upper limit of normal is 1.2 (this number also depends on several factors, especially how much muscle someone has), then with an ACE inhibitor like lisinopril, that 1.2 becomes something like 1.5. So, your level of 1.66 is closer to normal, but still elevated.

Second, flfluid status absolutely affffects the levels of BUN and creatinine in the blood, but volume depletion (what your doctor means when he says you are “dehydrated”) tends to affffffffffffect BUN more, so that we see a BUN:creatinine ratio of 20:1 or more in people who are very dry. Yours is 17.5, which is not consistent with volume depletion.

Third, people with severe congestive heart failure (which you must have had in order to get a heart transplant) often develop some damage to the kidney, as the heart is unable to give the kidney adequate blood, causing permanent damage to the kidney tubules.

I suspect you have some mild kidney damage, possibly related to your heart disease, and that the lisinopril is making your numbers appear worse. Paradoxically, the lisinopril helps protect the kidney from further damage. Don’t stop it unless advised to by your doctors.

Finally, keep an eye on what happens to the blood levels: If they rise steadily or quickly, that is a reason to see a kidney specialist.