A crucial test for detecting diabetic nephropathy early is the microalbuminuria test of small amounts of protein in the urine. A standard urinalysis can reveal larger amounts of protein in the urine (proteinuria), but at that stage the kidneys have sustained further damage that might have been prevented or delayed.

The American Diabetes Association (ADA) recommends that people with type 2 diabetes be tested for microalbuminuria at the time of their diagnosis and then once a year thereafter. People with type 1 diabetes should be tested five years after being diagnosed and then once a year thereafter. A physician may advise more frequent testing for a patient with additional risk factors, such as elevated blood pressure.

The most basic method to test for albumin is a urine dipstick test. A coated dipstick will change color if small amounts of albumin are present. A more precise measurement can be attained by testing over a specified period of time. A patient may be asked to collect a urine sample over a four- to 24-hour period.

Other diagnostic tests for diabetic nephropathy include:  

• Serum creatinine test. A blood test that measures the level of the waste product creatinine in the blood. Creatinine comes from two sources: meat products in the diet and from wear and tear on the muscles. Almost all of it eventually ends up in a person’s urine.
  
  
• Blood urea nitrogen (BUN) test. A blood test that determines the level of urea nitrogen in the blood. Urea nitrogen is produced from a breakdown of food protein.
  
  
• Creatinine urine test. A urine test that measures the amount of creatinine in the urine.
  
  
• Creatinine clearance test. A urine test that measures the amount of fluid filtered each minute by the kidneys.
  
  
• 24-hour urine protein test. A collection of all urine produced during one day that shows how many milligrams of protein are being lost in the urine.
  
  
• Glomerular filtration rate (GFR). An indirect measurement of the amount of glomerular filtrate (a substance similar to plasma but without proteins) formed in the kidneys each minute. GFR is estimated through other tests such as creatinine clearance, serum creatinine, inulin clearance (test involving timed urine collections after intravenous administration of a sugar called inulin) or equations such as the Modification of Diet in Renal Disease (MDRD) equation. A GFR of less than 60 indicates kidney damage, according to the National Kidney Disease Education Program.

  The American Heart Association issued a recommendation in 2006 that people who have or are at risk for cardiovascular disease consider undergoing tests of kidney function, especially the MDRD, because kidney disease is a major risk factor for diseases of the heart and blood vessels.

Recent research indicates that a blood test for a protein called cystatin C can reveal increased risk for chronic kidney disease and cardiovascular disease in elderly people with no known kidney problems, and that a cholesterol blood test for a substance called apolipoprotein A-IV may predict long-term risk of progressive kidney dysfunction in people with mild to moderate kidney disease. 

As diabetic nephropathy progresses, a biopsy may be performed to determine the specific amount of kidney damage. A small tissue sample will be extracted from the kidney to be analyzed.

There are five stages that are generally recognized as belonging to the progression of nephropathy. It is important to note that acute kidney failure, which is due to such causes as trauma or poisoning, rarely progresses to end-stage renal disease (ESRD). The five stages include:

• Stage I. The kidneys filter wastes at a level that is higher than normal. This process is known as hyperfiltration. Some patients remain at this level indefinitely, while others advance to the next stage after a period of years.
  
  
• Stage II. Filtration remains elevated, and damage to the glomeruli (filtering units) begins to appear. Small amounts of the blood protein albumin can begin to leak into the urine. This condition, microalbuminuria, usually becomes progressively worse. People with diabetes who control blood pressure and keep tight control over glucose (blood sugar) levels may remain in Stage II for years.
  
  
• Stage III. Also known as overt diabetic nephropathy, it occurs when albumin in the urine increases and the kidneys’ ability to filter wastes usually begins to decrease, causing a buildup of wastes. High blood pressure (hypertension) is a frequent complication of this kidney damage. Increased levels of damage to the glomeruli are evident. Blood levels of creatinine and urea-nitrogen rise. Patients frequently remain at this stage for years.
  
  
• Stage IV. Kidney filtration is substantially impaired.  Large amounts of protein pass into the urine, and high blood pressure is almost always present. Levels of creatinine and urea-nitrogen in the blood continue to rise.
  
  
• Stage V. The final stage of kidney disease involves chronic kidney failure as part of ESRD. Filtration is seriously impaired, and the kidneys are unable to regulate the body’s balance of salt and water. Production of urine slows or stops altogether. Waste products and water accumulate in the body, leading to a potentially life-threatening overload of these substances.