HbA1c tracked kidney decline as well as CGM; time in range did not

Design

Observational analysis within a randomised trial (GRADE-CGM substudy)

Population

1,363 adults with type 2 diabetes with ≥10 days of blinded CGM

Primary outcome

Cardiovascular events or death, and eGFR slope

Effect

eGFR slope −0.35 (GMI) and −0.38 (HbA1c) mL/min/1.73 m²/yr per 1%; time in range not associated

The GRADE-CGM substudy fitted 1,363 adults with type 2 diabetes from the GRADE trial with blinded CGM for at least 10 days, then compared time in range and the glucose management indicator (GMI) with HbA1c as predictors of cardiovascular events or death and of eGFR decline over a median 2.3 years.

All three metrics were associated with cardiovascular events or death: per 1% GMI (HR 1.44), per 1% HbA1c (HR 1.37) and per 20% time in range (HR 0.73). Higher GMI and HbA1c were each associated with faster eGFR decline, by about 0.35–0.38 mL/min/1.73 m² per year per 1%. Time in range was not associated with eGFR slope. When each CGM metric was adjusted for HbA1c, most associations weakened.

CGM metrics are increasingly reported in clinic, and some advocate replacing HbA1c with time in range. For kidney outcomes, this analysis suggests HbA1c and GMI carry similar information, and time in range does not track kidney decline. HbA1c can be unreliable in advanced CKD and anaemia, where GMI is a reasonable substitute.

It is observational, follow-up was short, and the CGM snapshot was taken once.

• Continue to use HbA1c as a marker of kidney risk in type 2 diabetes where it is reliable.
• Use the CGM-derived glucose management indicator where HbA1c is unreliable, such as advanced CKD or anaemia.
• Do not rely on time in range alone to judge kidney risk.
• Combine glycaemic control with established kidney-protective drugs and blood pressure control.

Why it matters

It tempers enthusiasm for replacing HbA1c with time in range in kidney risk assessment.

Don't overread it

Observational associations over 2.3 years; it does not show which target to treat to.

The statistics, in plain English

Hazard ratios per unit change show how risk rises with each step in the metric. The eGFR slope difference of about 0.35 mL/min/1.73 m² per year per 1% is modest but adds up over a decade. Attenuation after mutual adjustment means the metrics largely overlap.

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