The Effect of ACE Inhibitors on Kidney Function in Patients with Type 1 Diabetes

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The summary below is from the full report titled "Should All Patients with Type 1 Diabetes Mellitus and Microalbuminuria Receive Angiotensin-Converting Enzyme Inhibitors? A Meta-Analysis of Individual Patient Data." It is in the 6 March 2001 issue of Annals of Internal Medicine (volume 134, pages 370-379). The author is the ACE Inhibitors in Diabetic Nephropathy Trialist Group.

What is the problem and what is known about it so far?

In type 1 diabetes, the pancreas fails to produce insulin, a hormone that regulates the body's ability to store foods. Type 1 diabetes results in high blood sugar levels that can, over time, lead to complications, such as kidney failure. Controlling blood sugar helps prevent these complications. Blood pressure medications called angiotensin-converting enzyme (ACE) inhibitors can also help prevent diabetes-related kidney failure. It is therefore recommended that patients with diabetes take ACE inhibitors when a protein called albumin appears in the urine (albuminuria), a sign of kidney damage. It is unclear, however, whether patients with even very small amounts of albumin in the urine (microalbuminuria) benefit from ACE inhibitors. Previous studies have shown that ACE inhibitors slow kidney damage, but it is not known whether they can actually restore normal kidney function. Lowering blood pressure can by itself protect kidney function, but it is unclear whether ACE inhibitors protect kidney function in diabetic patients by reducing blood pressure or through some other action.

Why did the researchers do this particular study?

To find out whether 1) there is a level of albumin in the urine below which ACE inhibitors show no benefit, 2) ACE inhibitors can help damaged kidneys regain normal function, and 3) improved blood pressure explains the benefit of ACE inhibitors.

Who was studied?

646 patients with type 1 diabetes and microalbuminuria.

How was the study done?

Rather than doing a new study, the researchers used a technique called meta-analysis to combine information from selected previous studies. For a study to be included, patients must have been assigned randomly to receive either an ACE inhibitor, no ACE inhibitor, or a placebo (a pill that looked like an ACE inhibitor but contained no active ingredient) and must have been followed for at least 2 years. Each study also had to include at least 10 patients with normal blood pressure.

What did the researchers find?

The benefit of ACE inhibitors was greatest in patients with larger amounts of microalbuminuria, but patients with very little microalbuminuria also showed benefit. Kidney function was three times more likely to become normal in patients who received ACE inhibitors than in patients who did not receive them. The lowering of blood pressure with ACE inhibitors did not account for all of the improvement in kidney function.

What were the limitations of the study?

This study did not include children and was not designed to look for unfavorable side effects from ACE inhibitors.

What are the implications of the study?

Kidney function improves in patients with type 1 diabetes and microalbuminuria who take ACE inhibitors, regardless of the amount of microalbuminuria and independent of changes in blood pressure.