High-Normal Uric Acid and Lower GFR Linked, a Study Shows

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An inverse association between uric acid levels and renal function in type 1 diabetics.

 

Serum uric acid levels in the high-normal range are associated with reduced renal function in patients with type 1 diabetes, according to researchers.

 

A group led by Andrzej S. Krolewski, MD, of the Joslin Diabetes Center in Boston, studied 674 patients with type 1 diabetes, of whom 364 had normoalbuminuria (NA) and 311 had microalbuminuria (MA). Most subjects had normal uric acid levels and glomerular filtration rate (GFR). Hyperuricemia is defined as a serum uric acid level higher than 6.6 mg/dL in women and higher than 7.0 mg/dL in men.

 

Mildly or moderately impaired renal function (defined as an estimated GFR below 90 mL/min) was identified in 10% of NA patients and 36% of MA patients. Researchers estimated GFR from the serum concentration of cystatin C (cC-GFR).

 

Lower cC-GFR was strongly and independently associated with higher serum uric acid and higher urinary albumin excretion rate (AER), older age, and antihypertensive therapy. The MA group had a uric acid level of 5.2 mg/dL, which was significantly higher than the 4.2 mg/dL level observed in the NA group, the investigators reported in the Clinical Journal of the American Society of Nephrology (2008; published online ahead of print).

 

The mean cC-GFR was lower in the MA than the NA group (98.7 vs. 118.8 mL/min), but both values were in the normal range.

 

In the MA group, the mean uric acid level was 4.5 mg/dL in subjects with a GFR above 109 mL/min compared with 5.6 mg/dL in those with a cC-GFR below 109 mL/min. In the NA group, the mean uric acid level was 4.0 mg/dL in subjects with a GFR above 109 mL/min compared with 4.6 mg/dL in those with a cC-GFR below 109 mL/min.

 

Within each tertile of albumin excretion rate (AER), mean cC-GFR decreased progressively with increasing serum uric acid. Within each tertile of serum uric acid, mean GFR decreased progressively with increasing AER.

 

The adjusted mean cC-GFR was 108.1 and 97.5 among subjects in the middle and highest third tertile of uric acid (4.1-5.2 and 5.3 mg/dL or greater), respectively, compared with 117.4 mL/min among those in the lowest tertile (4.0 mg/dL or less). The adjusted mean cC-GFR was 109.4 and 97.6 mL/min among those in the second and third tertiles of AER (18.4-46.8 and 46.9 µg/min or greater) compared with 115.9 mL/min among subjects in the lowest tertile (18.3 µg/min or less).

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