Kidney Tests For Diabetics Or Prediabetes

The kidneys play a vital role in keeping toxins and contaminants out of the blood. They are the filter systems of the body that are responsible for removing unwanted materials and helping to retain components in the blood that are required for optimum functioning at the cellular level. Excessive levels of glucose, as seen in prediabetes and diabetes, will cause significant problems for the correct functioning of the kidneys and can, without regulation, lead to complete kidney failure. If this happens patients will be required to complete dialysis on regular bases to filter the blood and prevent the buildup of fluid and toxins in the body. Untreated kidney failure will result in severe toxicity in the body which can be fatal.

Kidneys and Glucose

The kidneys play an important role in the regulation of blood pressure along with the acid-base balance in the body and the electrolyte concentration. They play a role in the balancing of the plasma osmolality or the amount of fluid in the blood. When glucose levels are high on a constant basis, this causes dehydration at the cellular level, leading to increased thirst. More urine is produced further removing much needed fluid from the body.

The specific filtration function of the kidney occurs in small hollow filters known as glomeruli. The rate at which the kidney functions is known as the estimated glomerular filtration rate or eGFR and it decreases as kidneys become damaged due to high glucose levels and high blood pressure levels. When kidneys are not functioning properly, glucose and protein are released into the urine and, using tests, it is possible to determine how effectively the kidneys are functioning and if diabetes is a concern.  Normal kidneys will use approximately 10% of glucose consumed after an overnight fast and they will filter a total of about 180 grams of protein per day. 1

In the United States it is estimated that approximately 11.6% of the adult population has some form of chronic kidney disease. This is most commonly in the form of albuminuria (high protein levels in the urine) or a decrease in the estimated glomerular filtration rate which are both associated with diabetes and hypertension. 2

Symptoms Of Kidney Problems

Most people will have very few if any symptoms of kidney problems until the kidney is significantly damaged. The decrease in functioning can actually go unnoticed until there is almost complete renal failure. Some people will experience swelling of the extremities along with feelings of exhaustion and nausea. Kidney damage due to diabetes is typically very slow to develop but may actually be present years prior to the diagnosis of either type 1 or type 2 diabetes.

Typical people with risk factors for diabetes or a history of hypertension and prediabetes will be required to complete regular urine tests. These test check for the presence of protein in the urine, known as albuminuria or microalbuminuria. These tests typically occur once a year once the diagnosis is made. Another commonly administered test will check for the presence of ketones in the urine that are a result of hyperglycemia or elevated blood glucose levels in the body.

Microalbuminuria Test

Everyone eliminates small amounts of protein into the urine; however those individuals with prediabetes or diabetes that have some damage to the kidneys will have an increased level of protein in the urine. This occurs because of the damage to the tiny blood vessels around the glomeruli that leak protein into the waste material that is removed from the kidneys into the bladder and out through the urine.

This test can be performed using a test strip that is dipped in the urine and compared to a rating based on the indication of the test strip. A more in depth test is usually completed if there is any abnormal reading and can include a 24 hour urine collection that measures total protein excreted.  Random urine tests are also possible and can be performed at a doctor’s office or a clinical lab. Multiple tests may be required to confirm that diabetes, kidney disease and potential peripheral artery disease is present, often the microalbuminuria test is compared with the serum creatinine test for a more complete result.

Serum Creatinine Testing

The serum creatinine test checks the blood for the presence of creatinine, which is a metabolic by-product produced when muscles are contracting. Normally functioning kidneys filter out creatinine which is a waste product. Testing for high levels of creatinine in the blood plus the presence of albuminuria in the urine is considered to be proof positive that kidney functioning is impaired. The benefit of a creatinine test is that it can be used to calculated the eGFR that can determine the extent to which the kidney functioning is impaired.

Levels of creatinine higher than 1.2 mg/dL and 1.4 mg/dL for women and men respectively indicate that there is some limitation to the filtering ability of the kidneys. The test is two part, one blood test to determine blood creatinine levels and a urine test to also check for creatinine output. The difference, known as the creatinine clearance, forms the eGFR. The normal eGFR varies based on age, gender, and body type. Studies into using albumin and creatinine ratio to determine kidney functioning shows that this is a very effective test for determining those in high risk groups even with a moderate reduction in the eGFR. 3

Tests that check the levels of urea in the blood can also be used. These are less conclusive since a wide number of diseases and medical conditions can cause high urea levels in the blood without kidney damage.

References

1 Gerich, J. E. (2010). Role of the kidney in normal glucose homeostasis and in the hyperglycaemia of diabetes mellitus: therapeutic implications. Diabetic Medicine , 136-142.

2 Levey, A. S., Astor, B. C., Stevens, L. A., & Coresh, J. (2010). Chronic kidney disease, diabetes, and hypertension: what’s in a name? Kidney International , 19-22.

3 O’Hare, A. M., Hailpern, S. M., Pavkov, M. E., et al. (2010). Prognostic Implications of the Urinary Albumin to Creatinine Ratio in Veterans of Different Ages With Diabetes. Archives of Internal Medicine , 930-936.

This article was originally published July 12, 2012 and last revision and update of it was 9/10/2015.