What is creatinine?
Creatinine is a by-product of normal muscle breakdown. Measuring the levels of creatinine in the bloodstream and in the urine can be helpful for tracking the progression of diabetic kidney disease.
Diabetic nephropathy (kidney disease) caused by high blood glucose levels and high blood pressure, is the leading cause of kidney failure in the United States. Kidney failure develops within 10 years in 50% of people with Type 1 diabetes and overt kidney disease. In people with Type 2 diabetes and overt kidney disease, 20% progress to kidney failure in 20 years. Fortunately, taking a number of steps, such as controlling blood glucose levels and blood pressure, can reduce the risk of kidney failure. It’s also important to catch diabetic nephropathy as early as possible.
One of the best screening tools for the earliest stages of diabetic nephropathy is the microalbuminuria test. Once the kidneys become damaged, tiny amounts of protein leak into the urine, a condition known as microalbuminuria. Currently, the American Diabetes Association recommends starting to screen for microalbuminuria in people who have had Type 1 diabetes for five years and at the time of diagnosis in people with Type 2 diabetes (since Type 2 diabetes may have been developing and causing problems long before it was diagnosed). All people with diabetes should be screened annually thereafter (or within six months if a test result is positive for microalbuminuria).
While microalbuminuria is a very sensitive test in people with Type 1 diabetes, testing for microalbuminuria alone may miss many cases of diabetic kidney disease in those with Type 2. For that reason, some kidney experts now recommend also testing the glomerular filtration rate (GFR) annually in people with Type 2 diabetes. GFR is a measure of how well the kidneys are able to filter waste from the blood. A persistently low GFR indicates kidney disease.
How to calculate GFR from creatinine
Currently, GFR cannot be measured directly, but it can be closely approximated using the blood concentration of creatinine. Since healthy kidneys excrete creatinine in the urine, a buildup of creatinine in the bloodstream is a warning sign that kidney function is beginning to decline. By measuring the concentration of creatinine in the bloodstream and using it in an equation that takes into account the person’s weight, age, sex, and race, doctors can estimate the GFR to evaluate kidney function. The higher the blood creatinine level, the lower the GFR and the worse shape the kidneys are in. Some physicians also use the blood creatinine level and GFR calculation to track the decline of kidney function and to gauge any benefits of treatment.
What is creatinine clearance
Kidney function is also sometimes assessed using a test called creatinine clearance, which also approximates GFR. A blood sample is taken and urine is collected over a 24-hour period to measure the amount of creatinine cleared from the bloodstream over that period of time.