Long-Term HbA1c Levels May Help Determine Eye Complication Risk in People with T1D

Hans J. Arnqvist

More than 30 years of data suggest long-term weighted mean HbA1c since diagnosis of type 1 diabetes (T1D) was a strong biomarker for proliferative diabetic retinopathy (PDR) and nephropathy.

Study investigators from Linköping University in Sweden indicated that a HbA1c level of <7.0% can help people with T1D avoid both PDR and nephropathy.

“Our study determines accurately the levels of long-term sugar that can avoid complications,” wrote study author Hans J. Arnqvist, Department of Endocrinology, Linköping and Department of Biomedical and Clinical Sciences, Linköping University. “This knowledge can increase a person’s motivation to keep their blood sugar level under control.”

As a predictor of microvascular complications, Arnqvist and colleagues aimed to evaluate HbA1c from diagnosis of T1D to determine the severity of these complications. Using a population-based observational study, a total of 447 patients diagnosed with T1D before 35 years of age from 1983 to 1987 in Southeast Sweden were included.

The Vascular Diabetes Complications in Southeast Sweden (VISS) study followed this population from diagnosis until 2019. The long-term weighted mean HbA1c was calculated by integrating the area under all HbA1c values. Investigators analyzed the development of eye- and kidney damage between 32 and 36 years after diagnosis.

Complications were analyzed subsequently in relation to the weighted mean HbA1c into five levels. All 447 newly diagnosed patients in the region during this period were included in the study.

Over the period of 32 years, 9% of patients had no retinopathy, while 64% had non-PDR, and 27% had PDR. Moreover, 83% had no microalbuminuria, 9% had microalbuminuria, and 8% had macroalbuminuria.

Investigators found the lowest long-term weighted HbA1c levels associated with development of PDR and macroalbuminuria were 7.3% (56 mmol/mol) and 8.1% (65 mmol/mol), respectively.

They added that the prevalence of PDR and macroalbuminuria increased following increasing wHbA1c, being 74% and 44% in the highest category (wHbA1c >9.5% [>80 mmol/mol]), respectively.
Compared with the follow-up performed after 20 –24 year’s duration, the prevalence of PDR had increased from 14% to 27% and macroalbuminuria from 4% to 8%. Each appeared at lower weighted HbA1c values as well.

The study investigators noted that these 30-year findings, in comparison with the 20-year follow-up, indicate that damage had arisen at lower blood sugar levels than was the case after 20 years.

They added that with an increase in the number of patients who experienced damage, the threshold for developing complications seems to fall gradually with time.

As a result, Arnqvist and colleagues noted that the study does not offer conclusions for the recommended blood sugar level of people with T1D longer than 30 years after diagnosis.

“The risk of eye- and kidney complications increases as the level increases,” noted Arnqvist. “Our conclusions relate to avoiding complications arising from blood vessel damage. But if a patient has problems with low blood sugar, hypoglycaemia, it’s not possible to control the blood sugar level so strictly.”

The study, “Impact of HbA1c Followed 32 Years From Diagnosis of Type 1 Diabetes on Development of Severe Retinopathy and Nephropathy: The VISS Study,” was published in Diabetes Care.