How does TIR compare with A1c?
Dr. Goldenberg and colleagues set out to better understand how the emerging TIR metric compares with the traditional A1c value.
They performed a post-hoc analysis of data from the phase 4 SWITCH PRO study of basal insulin–treated patients with type 2 diabetes with at least one risk factor for hypoglycemia.
The patients were treated with insulin degludec or glargine 100 during a 16-week titration and 2-week maintenance phase, and then crossed over to the other treatment for the same time periods.
Glycemic control was evaluated using a blinded professional CGM (Abbott Freestyle Libro Pro). The primary outcome was TIR, which was defined as the percentage of time spent in the blood glucose range of 70-180 mg/dL.
There were 419 participants in the full analysis. Patients were a mean age of 63 and 48% were men. They had a mean body mass index of 32 kg/m2 and had diabetes for a mean of 15 years.
There was a moderate inverse linear correlation between TIR and A1c at baseline, which became stronger following treatment intensification during the maintenance periods in the full cohort, and in a subgroup of patients with median A1c ≥ 7.5% (212 patients).
This correlation between TIR and A1c was poorer in the subgroup of patients with baseline median A1c < 7.5% (307 patients).
The data were widely scattered, “supporting the premise that A1c and TIR can be relatively crude surrogates of each other when it comes to individual patients,” Dr. Goldenberg and colleagues note.
Where individual patients have both low A1c and low TIR values, this might indicate frequent episodes of hypoglycemia.
A few individual patients had TIR > 70% but A1c approaching 9%. These patients may have different red blood cell physiology whereby A1c does not reflect average glycemic values, the researchers suggest.
The study was sponsored by Novo Nordisk and several authors are Novo Nordisk employees. The complete author disclosures are listed with the article. Dr. Thomas has reported no relevant financial relationships.
A version of this article first appeared on Medscape.com.