DEAR DR. ROACH: I have Type 2 diabetes, which is under control, but my creatinine level fluctuates between 2.2 and 3, staying mostly at 2.6. I am asymptomatic and feel fine. I have no swelling in my ankles, and my blood pressure is within normal range. I am 75 years old. I weigh 242 pounds, and I am 6 feet, 3 inches tall. All my electrolytes are within range. Can you explain the significance of the creatinine numbers on my kidneys? I may be going for a knee replacement soon, and my doctor says it is a stress on the kidneys and is cautious. — S.W.
ANSWER: Creatinine is a waste product of muscles. Everybody has it in their blood. The kidneys get rid of creatinine, as well as many other waste products. So, a higher creatinine level means the kidneys aren’t doing as good a job at getting rid of waste products in the blood. Creatinine doesn’t hurt the kidneys. A normal level is usually around 1, and a level of 2 means roughly that the kidneys are only working half as well as they ought to. Of course, people vary in their levels; those who are more muscular usually have a higher level. With very poor kidney function the creatinine level may be as high as 10, this is typically about the time people are starting dialysis (which is basically an artificial kidney outside the body for a few hours several times weekly). At that point, potassium levels may be dangerously high — a very common reason for dialysis to start.
Kidney function, as approximated by creatinine level, affects one’s risk during surgery. A creatinine level greater than 2 means there is a higher risk of both heart and lung complications around the time of surgery. Also, many medications need to have a different dosing since the kidney gets rid of many medications. Your doctor is wise to be cautious.