written by Michael O’Leary
If you have type 2 diabetes and chronic kidney disease, lowering your HbA1c too much may be as bad as not lowering it enough. That’s the conclusion of another study of people who have diabetes and stage 3 or 4 kidney disease. The study appears in this month’s Archives of Internal Medicine.
There were 23,296 patients in this study, all had been hospitalized in Alberta, Canada with stage 3 or 4 chronic kidney disease and type 1 or 2 diabetes. The researchers led by Dr. Marcello Tonnelli, of the University of Alberta in Edmonton, analyzed their medical records and categorized them by blood glucose control based on the first HbA1c measurement taken during the study period. They then tracked subsequent hospitalizations, heart attacks and other heart-related events as well as progression of the kidney disease. (Link to published site)
At the start of the study the median HbA1c was 6.9 percent, meaning half the people had blood sugar levels higher than that and half had lower levels than that.
The results of the study reported on by MedPage Today showed that after a median of four years, 16 percent of the patients had died, 49 percent had been hospitalized again, 16 percent had a heart-related event, 6 percent had their kidney disease get worse based on a doubling of their creatinine, (a measure of kidney function) and 2 percent had their kidneys fail.
The researchers made adjustments for age, sex, kidney function at the start of the study, other diseases present, and some demographic differences such age, sex, income, neighborhood locations.
When they graphed the results, they found that the shape of the graph of those who died looked line a U, with equal numbers of those who died had a HbA1c level lower than 6.5 percent as those with a HbA1c higher than 8 percent.
When they looked at progression of the kidney disease, however, they found that those whose disease advanced most during the study had milder chronic kidney disease at the start of the study. Tonnelli and his researchers concluded that this suggests that once kidney function begins to decline, blood sugar control may not be enough to prevent advancing kidney disease.
An alternative explanation offered by Dr. David Goff, Jr. of Wake Forest University in Winston-Salem in an editorial opinion about the study that also appeared in the journal suggests that there may be little clinical connection between blood sugar control and advancing kidney disease in people who are already have stage 3 or 4 kidney disease.
“The lack of internal consistency for these two renal outcomes [incident end-stage renal disease and disease progression] raises some uncertainties regarding the clinical importance of the differential association of HbA1c level with end-stage renal disease between stage 3 and stage 4 chronic kidney disease,” he wrote.
Because this kind of observational study cannot resolve this question about the effects of blood sugar control on stage 3 or 4 kidney disease, both Tonelli and Goff call for randomized controlled clinical trials designed to determine whether overly intensive therapy worsens outcomes in patients with diabetes and chronic kidney disease.
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