Diabetes is a major risk factor for kidney disease; around 30% of people with type 1 diabetes and 10-40% of those with type 2 diabetes will go on to experience kidney failure. But new research finds that even before a diabetes diagnosis, higher-than-normal blood sugar levels could be causing kidney damage.

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Researchers suggest prediabetes may be a precursor to kidney disease.

Study coauthor Dr. Toralf Melsom, of the Department of Nephrology at University Hospital of North Norway, and colleagues publish their findings in the American Journal of Kidney Disease.

Around 86 million people in the US have prediabetes - blood sugar levels that are higher than normal but not high enough to receive a diabetes diagnosis.

According to the Mayo Clinic, without interventions - such as increasing physical activity, losing weight and adopting a healthy diet - an individual with prediabetes is likely to be diagnosed with type 2 diabetes within 10 years.

Dr. Melsom and colleagues note that previous research has attempted to discover an association between prediabetes and kidney damage, but they note that such studies have produced inconsistent results, which the team attributes to the use of estimates of glomerular filtration rate (GFR) rather than measured GFR (mGFR).

GFR is a kidney function test that measures how much blood passes through the glomeruli - the small filters in the kidneys that filter waste from the blood - every minute. Higher GFR is a sign of hyperfiltration - a kidney abnormality that can lead to kidney damage and failure over time.

Targeting prediabetes could prevent kidney disease

For this latest study, the team measured the GFR, fasting glucose (FG) levels and/or HbA1c levels of 1,324 adults aged 50-62 in order to gain a better understanding of whether prediabetes is linked to kidney damage.

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In the study, prediabetes was classed as an FG level of 110-125 mg/dL (6.1-6.9 mmol/l) and/or an HbA1c level of 6-6.4%, as defined by the International Expert Committee of 2009, or as an FG of 100-125 mg/dL (5.6-6.9 mmol/l) and/or an HbA1c of 5.7-6.4%, as defined by the American Diabetes Association.

The presence of prediabetes among study participants was assessed at study baseline, and subjects were followed-up for a median of 5.6 years. At study baseline, 595 of the participants had prediabetes.

After adjusting for participants' lifestyle and use of medications, the researchers found those with prediabetes had a higher mGFR during follow-up than those without prediabetes - a sign of hyperfiltration in the kidneys.

What is more, the researchers found that high FG levels at baseline among these subjects were associated with high levels of the protein albumin in the urine during follow-up - an early sign of kidney disease.

According to the researchers, these findings suggest that both FG ad HbA1c levels that are consistent with prediabetes are independent risk factors for kidney hyperfiltration and high albumin in the urine, indicating that prediabetes may be a precursor to kidney disease.

Commenting on the study results, Dr. Melsom says:

"Our research shows that the pathological process of kidney injury caused by elevated blood glucose levels starts in prediabetes, well before the onset of diabetes.

[...] Prediabetes may be a target for early intervention to prevent chronic kidney disease (CKD) caused by hyperglycemia. If a patient has borderline elevated glucose levels found by their primary physician they should start lifestyle changes with respect to diet and physical activity to preventing diseases like diabetes and kidney disease."

Dr. Jeffrey Berns, president of the National Kidney Foundation, adds that the study also "makes a strong case" for increased use of mGFR over estimated GFR in clinical research, especially for patients with relatively normal kidney function.

Earlier this year, Medical News Today reported on a study linking the commonly used heartburn drugs proton pump inhibitors (PPIs) to increased risk of kidney disease.