If a test shows the presence of albumin in the urine, the physician usually orders one or two repeat tests to confirm the result (because albumin levels in urine can vary from day to day). To reach a firm diagnosis of microalbuminuria, a person needs to have certain levels of albumin in the urine on at least two of three tests in three to six months. The more albumin that is in the urine, the more severe the kidney disease.
Currently, the American Diabetes Association (ADA) recommends starting to screen for microalbuminuria in people who have had Type 1 diabetes for 5 years and at the time of diagnosis in people with Type 2 diabetes (since diabetes may have been developing and causing problems for many years before diagnosis). All people with diabetes should be screened annually after their first microalbumin test (or have repeat testing within six months if a test result is positive for microalbuminuria).
While microalbuminuria may be a very sensitive test in people with Type 1 diabetes, there is evidence that testing for microalbuminuria alone may miss many cases of diabetic kidney disease in people with Type 2 diabetes. In a study reported in the June 25, 2003, issue of The Journal of the American Medical Association, researchers studied data from 1,197 people with Type 2 diabetes who were 40 years or older. In addition to testing for microalbuminuria, they tested participants’ glomerular filtration rate (GFR), a measure of how well the kidneys are able to filter waste from the blood. GFR is considered the best gauge of kidney function (and is the measure the NKF uses to divide up its five-stage kidney disease classification system), and a persistently low GFR indicates kidney disease. Of those study subjects who had a low GFR, 55% did not have microalbuminuria. So some medical experts now recommend that people with Type 2 diabetes also have their GFR tested annually to catch early nephropathy that a microalbumin test may miss.
GFR cannot be measured directly. Currently, it is closely approximated, in part, by using the blood concentration of creatinine. Healthy kidneys excrete creatinine in the urine, so a buildup of creatinine in the blood shows that the kidneys aren’t working well. 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 and get a sense of kidney function. The higher the blood creatinine level, the lower the GFR. 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.
Prevention and treatment
At least two large studies have shown beyond a shadow of a doubt that tight blood glucose control can significantly lower the risk of developing microalbuminuria and diabetic kidney disease. The glycosylated hemoglobin (HbA1c) test gives a measure of one’s long-term control of blood glucose and hence one’s risk for (diabetic complications. The ADA currently recommends that people with diabetes have an HbA1c test two to four times each year and strive for an HbA1c level under 7%.
Controlling blood pressure is important not only for reducing the risk of cardiovascular disease but also for protecting the kidneys. According to the ADA, both high systolic blood pressure (the pressure at the moment of the heart beat) and high diastolic pressure (the pressure between beats) can speed up the progression of diabetic kidney disease, and aggressive treatment of high blood pressure can greatly decrease the rate of fall in GFR. Treating high blood pressure has also been shown to raise life expectancy and reduce the need for dialysis and transplantation once diabetic kidney disease has developed. According to the ADA, people with diabetes should strive to maintain a systolic blood pressure under 130 mm Hg and a diastolic pressure under 80 mm Hg.